WEEK 5 Flashcards
(269 cards)
1
Q
What is MRSA?
A
MRSA stands for Methicillin-Resistant Staphylococcus Aureus, a type of staph bacteria that is resistant to methicillin and other similar antibiotics.
2
Q
What is methicillin?
A
Methicillin is a type of penicillin antibiotic that was developed to overcome resistance from some staph bacteria, but now many strains are resistant to it.
3
Q
Where do MRSA infections occur?
A
MRSA can cause infections both in hospitals and healthcare settings (nosocomial) and in the general community.
4
Q
What is VRSA or GISA?
A
VRSA stands for Vancomycin-Resistant Staphylococcus Aureus, and GISA stands for Glycopeptide-Intermediate Staphylococcus Aureus; these are staph bacteria that are resistant or partially resistant to vancomycin.
5
Q
What are glycopeptide antibiotics?
A
Glycopeptide antibiotics are a class of drugs, like vancomycin, that work by interfering with bacterial cell wall synthesis and are often used for serious Gram-positive infections.
6
Q
What is VRE?
A
VRE stands for Vancomycin-Resistant Enterococci, which are types of enterococci bacteria that have become resistant to the antibiotic vancomycin.
7
Q
What are enterococci?
A
Enterococci are bacteria that normally live in the intestines and female genital tract but can cause infections if they spread to other parts of the body, especially in hospital settings.
8
Q
In which patients do VRE cause particular problems?
A
VRE can cause serious problems in patients whose immune systems are weakened (immunosuppressed), such as those in intensive care units (ICU).
9
Q
What are Extended Spectrum β-Lactamases (ESBLs) associated with?
A
ESBLs are associated with resistance in bacteria like P. stuartii (causing UTIs), Klebsiella pneumoniae (causing bacterial pneumonia), P. aeruginosa (in cystic fibrosis), and E. coli.
10
Q
What is P. stuartii?
A
P. stuartii (Providencia stuartii) is a bacterium that can cause infections, particularly urinary tract infections (UTIs), and can carry resistance genes like ESBLs on plasmids.
11
Q
How are ESBLs mediated (spread)?
A
ESBL resistance can be spread through plasmids (small, transferable pieces of DNA) or can be part of the bacteria’s main genetic material (chromosomally mediated).
12
Q
What antibiotics do ESBLs inactivate?
A
ESBLs can inactivate (hydrolyse) even third-generation cephalosporins, but they generally do not inactivate carbapenems.
13
Q
What other resistances can plasmids carrying ESBL genes confer?
A
Plasmids carrying ESBL genes also often confer resistance to aminoglycoside antibiotics (like gentamicin) by changing the ribosome, and to quinolones (like nalidixic acid) by altering DNA gyrase.
14
Q
What is gentamicin?
A
Gentamicin is an aminoglycoside antibiotic used to treat many types of bacterial infections, especially those caused by Gram-negative bacteria.
15
Q
What is nalidixic acid?
A
Nalidixic acid is an older quinolone antibiotic primarily used to treat urinary tract infections.
16
Q
What is DNA gyrase?
A
DNA gyrase is an enzyme in bacteria that helps manage the coiling and uncoiling of DNA during replication and transcription; it’s a target for quinolone antibiotics.
17
Q
What is peptidoglycan?
A
Peptidoglycan is a polymer made of sugar and peptide (protein-like) units that forms the main structural component of prokaryotic (bacterial) cell walls.
18
Q
How are Gram positive bacteria characterized visually and structurally?
A
Gram positive bacteria stain purple with crystal violet-iodine dye and are surrounded by a cytoplasmic membrane and a thick cell wall containing peptidoglycan linked to teichoic acids.
19
Q
What are teichoic acids?
A
Teichoic acids are polymers containing phosphate and sugar alcohol units (polyhydroxylated phosphate polymers) found in the cell walls of Gram positive bacteria, helping to maintain cell wall structure and integrity.
20
Q
How is the cell wall of Gram negative bacteria structured?
A
Gram negative bacteria have a thinner cell wall (made of peptidoglycan and associated proteins) which is surrounded by an additional outer membrane composed of lipid, lipopolysaccharide, and protein.
21
Q
What is lipopolysaccharide (LPS)?
A
Lipopolysaccharide (LPS), also known as endotoxin, is a large molecule found in the outer membrane of Gram-negative bacteria that can cause strong immune responses in humans.
22
Q
What is the function of the complex cell wall in bacteria?
A
The complex cell wall helps protect bacteria against the influx of water that could occur due to a higher salt concentration inside the cell compared to outside.
23
Q
How do β-Lactams interfere with peptidoglycan formation?
A
β-Lactams interfere with peptidoglycan formation by interacting with Penicillin Binding Proteins (PBPs).
24
Q
How are PBPs classified?
A
PBPs are classified by their size, with PBP1 being the biggest, PBP2 the next, and so on.
25
What are the essential roles of PBPs in peptidoglycan synthesis?
PBPs are crucial in the final stages of building the peptidoglycan layer; their activities include acting as D-alanine carboxypeptidase, removing D-ala, and as peptidoglycan transpeptidase and endopeptidase.
26
What is D-alanine carboxypeptidase activity?
D-alanine carboxypeptidase activity is an enzymatic function of PBPs that removes the final D-alanine amino acid from peptidoglycan precursor units during cell wall construction.
27
What is peptidoglycan transpeptidase activity?
Peptidoglycan transpeptidase activity is the key enzymatic function of PBPs that creates cross-links between peptide chains in the peptidoglycan, strengthening the cell wall.
28
What is peptidoglycan endopeptidase activity?
Peptidoglycan endopeptidase activity is an enzymatic function that can cut existing peptidoglycan cross-links, allowing for cell wall reshaping during growth and division.
29
What is the basic structure of peptidoglycan?
Peptidoglycan consists of parallel sugar backbones made of alternating units called NAG (N-Acetylglucosamine) and NAM (N-Acetylmuramic acid).
30
What is N-Acetylglucosamine (NAG)?
N-Acetylglucosamine (NAG) is one of the two alternating sugar molecules that make up the backbone of bacterial peptidoglycan.
31
What is N-Acetylmuramic acid (NAM)?
N-Acetylmuramic acid (NAM) is the other sugar molecule in the peptidoglycan backbone, and it's the one to which short peptide chains are attached.
32
How are peptide chains attached to the sugar backbone?
Peptide chains are attached to the NAM sugar units through their carboxylic acid group.
33
How are peptide chains linked together in peptidoglycan?
These peptide chains are then linked together by crosslinks, which provide extra strength to the cell wall.
34
What enzyme catalyses the formation of these crosslinks?
The formation of these crosslinks is catalysed (helped along) by an enzyme called peptidoglycan transpeptidase (which is a PBP).
35
What is the effect of β-lactams on this crosslinking process?
β-lactam antibiotics inhibit the crosslinking of these peptide chains, weakening the cell wall.
36
What do the chemical structures on page 33 represent?
The structures show N-Acetylglucosamine (NAG) and N-Acetylmuramic acid (NAM), the two sugar building blocks of peptidoglycan.
37
What does the diagram on page 34 visually represent?
The diagram shows the repeating NAG-NAM sugar backbone of peptidoglycan, with peptide side chains attached to NAM units, and how these side chains are cross-linked to form a mesh-like structure.
38
How does the diagram show the peptide chains extending from NAM?
The diagram depicts short chains of amino acids (peptides) attached to each NAM molecule in the sugar backbone.
39
How does the diagram illustrate the cross-linking between peptide chains?
The diagram shows bridges connecting the peptide chains from one NAM-peptide unit to another on an adjacent peptidoglycan strand, forming a strong, interconnected network.
40
How do β-Lactams specifically act on the transpeptidase enzyme (PBP)?
β-Lactams bind covalently (form a strong chemical bond) to the active site of the transpeptidase enzyme.
41
What is an active site of an enzyme?
The active site of an enzyme is the specific region where the substrate (the molecule the enzyme works on) binds and where the chemical reaction takes place.
42
What is the consequence of β-Lactams binding to the enzyme's active site?
This binding prevents the normal peptidoglycan fragments (specifically the D-Ala residue) from accessing the active site and stops the enzyme from forming cross-links.
43
What does the diagram on page 35 illustrate?
The diagram shows a β-lactam antibiotic molecule attacking and binding to the active site (containing a hydroxy group from a serine residue) of the transpeptidase enzyme (PBP), thereby inactivating it.
44
What are two other agents, besides β-lactams, that target cell wall synthesis?
D-Cycloserine (DCS) and Vancomycin are two other antibacterial agents that also target bacterial cell wall synthesis.
45
Do these agents target the same step in cell wall synthesis?
No, peptidoglycan biosynthesis involves a number of steps, and these agents target different parts of the process.
46
What enzymes does Cycloserine (Seromycin) inhibit?
Cycloserine (brand name Seromycin) inhibits two key bacterial enzymes: alanine racemase (ALR) and D-Ala-D-Ala ligase (Ddl).
47
What is alanine racemase (ALR)?
Alanine racemase (ALR) is a bacterial enzyme that converts L-alanine (the common form of the amino acid alanine) into D-alanine, which is needed for the cell wall.
48
What is D-Ala-D-Ala ligase (Ddl)?
D-Ala-D-Ala ligase (Ddl) is a bacterial enzyme that joins two D-alanine molecules together to form D-Ala-D-Ala, a crucial component for peptidoglycan synthesis.
49
What type of antibiotic is Vancomycin (Vancocin)?
Vancomycin (brand name Vancocin) is a glycopeptide antibiotic.
50
How does Vancomycin interfere with cell wall synthesis?
Vancomycin prevents the release of the disaccharide-peptide building block (the NAG-NAM unit with its peptide chain) from its lipid carrier molecule in the cell membrane, so it can't be added to the growing cell wall.
51
What does the diagram on page 37 represent in cell wall synthesis?
The diagram illustrates the process of forming crosslinks in the bacterial cell wall, specifically showing how peptide chains link together.
52
What are the components of the peptide chain shown ready for crosslinking (e.g., L-Ala, D-Glu, L-Lys, D-Ala, D-Ala)?
These are specific amino acids (L-Alanine, D-Glutamic acid, L-Lysine, and two D-Alanine residues) that make up the short peptide side chain attached to the NAM sugar in peptidoglycan.
53
What is the role of the enzyme (ENZYME OH) in this crosslinking process?
The enzyme, which is a transpeptidase (PBP), facilitates the linking of one peptide chain to another. The 'OH' indicates a hydroxyl group in its active site.
54
How is the crosslink formed according to the diagram?
The enzyme helps to remove the terminal D-Ala from one peptide chain and then forms a new bond between the remaining D-Ala of that chain and a glycine (or other amino acid) in a neighboring peptide chain.
55
What happens to the terminal D-Ala on one of the peptide chains?
The very last D-Ala (the second D-Ala in the D-Ala-D-Ala pair) is removed from one of the peptide chains during the crosslinking reaction.
56
What is the final result shown in the diagram?
The final result is two peptidoglycan strands now linked together by a peptide cross-bridge, strengthening the overall cell wall structure.
57
Where does D-Cycloserine (DCS) come from?
D-Cycloserine (DCS) is produced by bacteria called Streptomyces garyphalus and Streptomyces lavendulae.
58
What is D-Cycloserine used to treat?
It can be used in the treatment of tuberculosis.
59
Why is D-Ala-D-Ala needed for bacterial cell wall synthesis?
D-Ala-D-Ala is a specific dipeptide (two amino acids joined) required as a building block for the peptide chains in the bacterial cell wall.
60
Is D-Ala the natural enantiomer of alanine?
No, D-Ala is the 'unnatural' enantiomer (mirror image form) of alanine; L-alanine is the form typically found in proteins.
61
What is an enantiomer?
Enantiomers are pairs of molecules that are mirror images of each other.
62
What can D-Cycloserine be used for?
It can be used in the treatment of tuberculosis.
63
Why is D-Ala-D-Ala needed for bacterial cell wall synthesis?
D-Ala-D-Ala is a specific dipeptide required as a building block for the peptide chains in the bacterial cell wall.
64
Is D-Ala the natural enantiomer of alanine?
No, D-Ala is the 'unnatural' enantiomer of alanine; L-alanine is the form typically found in proteins.
65
What is an enantiomer?
Enantiomers are pairs of molecules that are mirror images of each other and can have different biological activities.
66
How do bacteria produce D-Ala?
Bacteria must make D-Ala from the natural L-Ala using an enzyme called alanine racemase (ALR).
67
What does alanine racemase (ALR) do?
Alanine racemase converts L-alanine into a mixture of L-alanine and D-alanine or D-alanine into the same mixture.
68
What is a racemic mixture?
A racemic mixture is a 50:50 mixture of two enantiomers.
69
Is the action of ALR a common type of enzymatic process?
The destruction of chirality by ALR is a rare example of this type of enzymatic process.
70
What is chirality?
Chirality is a property of a molecule that is not superimposable on its mirror image.
71
What co-factor does ALR use?
ALR uses pyridoxal 5'-phosphate (PLP) as a co-factor to help it cause racemisation.
72
What is pyridoxal 5'-phosphate (PLP)?
PLP is the active form of vitamin B6 and acts as a co-factor for many enzymes involved in amino acid metabolism.
73
How does PLP help in racemisation?
PLP helps by forming an imine with the alanine, which increases the acidity of the α-hydrogen.
74
What is an imine (Schiff's base)?
An imine is a chemical compound containing a carbon-nitrogen double bond, formed when an amine reacts with an aldehyde or ketone.
75
How does DCS inhibit alanine racemase?
DCS inhibits alanine racemase, preventing the formation of the D-Ala needed for cell wall crosslink formation.
76
What other enzyme does DCS inhibit?
DCS also inhibits D-Ala-D-Ala ligase (Ddl).
77
What is the role of D-Ala-D-Ala ligase (Ddl)?
Ddl is the enzyme responsible for coupling two D-Ala residues to give the D-Ala-D-Ala dipeptide.
78
What happens to the D-Ala-D-Ala dipeptide?
This D-Ala-D-Ala dipeptide is then added to the end of the L-Lysine residue in the peptide chain.
79
What does the diagram on page 39 represent regarding Alanine Racemase (ALR)?
The diagram visually explains the mechanism of how Alanine Racemase (ALR) converts L-Alanine to D-Alanine.
80
How is PLP shown interacting with L-Alanine in the diagram?
PLP is shown forming a Schiff base linkage with L-Alanine within the active site of the ALR enzyme.
81
What key step is depicted that allows for the conversion between L- and D-Alanine?
The diagram shows the removal of the alpha-hydrogen from the alanine, creating a planar intermediate.
82
How does D-Cycloserine interfere with this process?
D-Cycloserine would bind to the enzyme and disrupt its normal function.
83
What does the diagram on page 40 illustrate regarding D-Ala-D-Ala Ligase?
The diagram shows how D-Ala-D-Ala Ligase uses ATP to join two molecules of D-Alanine together.
84
What is ATP?
ATP (adenosine triphosphate) is the main energy currency of the cell.
85
How is ATP involved in the D-Ala-D-Ala Ligase reaction?
ATP is used by the enzyme to activate one of the D-Ala molecules.
86
What are the inputs and outputs of the D-Ala-D-Ala Ligase reaction?
The inputs are two D-Ala molecules and ATP; the outputs are one D-Ala-D-Ala molecule, ADP, and an inorganic phosphate.
87
How would D-Cycloserine affect the D-Ala-D-Ala ligase enzyme?
D-Cycloserine can bind to it and prevent it from properly joining two D-alanines together.
88
Is Cycloserine available orally?
Yes, Cycloserine is an antibiotic that can be taken by mouth.
89
What is the spectrum of Cycloserine?
Cycloserine has a broad spectrum, meaning it can affect a wide range of different bacteria.
90
How is Cycloserine often used in TB treatment?
It is used in combination therapies for the treatment of tuberculosis.
91
Does Cycloserine have serious side-effects?
Yes, Cycloserine can have serious side-effects, including depression and convulsions.
92
Why does Cycloserine cause these neurological side-effects?
These side-effects are due to Cycloserine binding as an agonist to NMDA receptors in the brain.
93
What are NMDA receptors?
NMDA receptors are proteins found on nerve cells in the brain that are important for learning and memory.
94
What other effect does Cycloserine have on neurotransmitters?
Cycloserine also inhibits enzymes that metabolize and synthesize the neurotransmitter GABA.
95
What is GABA?
GABA is an important neurotransmitter in the brain that generally has a calming effect on nerve activity.
96
How can bacteria become resistant to Cycloserine?
Resistance can occur if the bacteria start to over-produce the D-Ala racemase enzyme.
97
What is the chemical structure of D-Cycloserine (DCS)?
The diagram shows D-Cycloserine as a five-membered ring containing an oxygen and two nitrogen atoms.
98
What is Vancomycin (Vancocin) produced by?
Vancomycin is a glycopeptide antibiotic produced by a bacterium called Streptomyces orientalis.
99
What is Vancomycin considered for MRSA treatment?
Vancomycin is often the last resort antibiotic in the treatment of MRSA (Methicillin-Resistant Staphylococcus Aureus) infections.
100
Is Vancomycin absorbed well when taken orally?
No, Vancomycin is not absorbed orally (by mouth).
101
How is Vancomycin usually administered?
Because it's not absorbed orally, Vancomycin is usually given by intravenous (i.v.) injection.
102
What are potential toxicities of Vancomycin?
Vancomycin can be toxic to the ears (ototoxicity) and kidneys (nephrotoxicity).
103
When is oral Vancomycin used?
Oral Vancomycin is used specifically in the treatment of Clostridioides difficile-associated disease (CDAD), as it needs to act directly in the gut.
104
What is Clostridioides difficile-associated disease (CDAD)?
CDAD is an infection of the colon caused by the bacterium Clostridioides difficile (C. diff), often leading to diarrhea and inflammation, typically after antibiotic use has disrupted normal gut bacteria.
105
What does MRSA stand for?
MRSA stands for Methicillin-Resistant Staphylococcus Aureus.
106
What kind of infections can S. aureus cause?
S. aureus (Staphylococcus aureus) can cause skin infections like boils, as well as more serious conditions such as toxic shock syndrome (TSS), pneumonia, septicaemia (blood poisoning), and meningitis.
107
What is toxic shock syndrome (TSS)?
Toxic shock syndrome (TSS) is a rare but serious condition caused by bacterial toxins, leading to fever, rash, low blood pressure, and potentially organ failure.
108
What is septicaemia?
Septicaemia, also known as sepsis or blood poisoning, is a life-threatening condition that arises when the body's response to an infection injures its own tissues and organs.
109
When were penicillin-resistant strains of S. aureus known?
Strains of S. aureus that were resistant to penicillin have been known since the 1960s.
110
When did epidemic MRSA (EMRSA) strains emerge?
Epidemic MRSA (EMRSA) strains, which spread easily, emerged in the 1990s.
111
What are the two genetic reasons for MRSA resistance?
MRSA resistance is due to: 1) a plasmid (blaZ) mediated β-lactamase enzyme AND 2) a chromosomal gene (mecA) acquired from another bacterium.
112
What does the blaZ gene do?
The blaZ gene produces a β-lactamase enzyme that can break down some penicillin-like antibiotics.
113
What does the mecA gene code for?
The mecA gene codes for an altered Penicillin Binding Protein called PBP-2a.
114
How does PBP-2a contribute to resistance?
PBP-2a has a decreased affinity (it doesn't bind well) for β-lactam antibiotics, so these antibiotics can't effectively stop cell wall synthesis.
115
Does the mecA gene confer resistance to other antibiotics?
Yes, the mecA gene is often associated with resistance to many other antibiotics, such as ciprofloxacin, erythromycin, and trimethoprim-sulfamethoxazole.
116
What is ciprofloxacin?
Ciprofloxacin is a fluoroquinolone antibiotic used to treat a variety of bacterial infections.
117
What is erythromycin?
Erythromycin is a macrolide antibiotic used for various bacterial infections, often as an alternative for people allergic to penicillin.
118
What is trimethoprim-sulfamethoxazole?
Trimethoprim-sulfamethoxazole (often called Co-trimoxazole) is a combination antibiotic that interferes with folic acid synthesis in bacteria.
119
What is the only available oral antibacterial agent for treating MRSA infections mentioned?
Linezolid (brand name Zyvox) is mentioned as the only available oral antibacterial for treating MRSA infections at the time of the document.
120
What is Linezolid?
Linezolid is an oxazolidinone antibiotic used to treat serious infections caused by Gram-positive bacteria, including MRSA and VRE.
121
What does the chemical structure on page 43 show?
The diagram shows the chemical structure of Linezolid (Zyvox).
122
What are other names for Clostridioides difficile?
Clostridioides difficile is also known as C. difficile, C.diff, and was formerly called Clostridium difficile.
123
What are the characteristics of Clostridioides difficile?
It is a spore-forming, rod-shaped, Gram positive bacterium.
124
What are spores in bacteria?
Bacterial spores are dormant, tough, non-reproductive structures produced by some bacteria, allowing them to survive harsh conditions.
125
Where is C. difficile present in the adult population?
It is present in the colon of 2-5% of the healthy adult population without causing problems.
126
What can lead to C. difficile infection?
C. difficile infection can result from (prolonged) exposure to broad-spectrum antibiotics (like cephalosporins or quinolones), which disrupt the normal balance of gut bacteria.
127
What happens after antibiotic treatment that can lead to C. difficile issues?
After antibiotic treatment, toxin-producing strains of C. difficile can overgrow and lead to antibiotic-associated diarrhea.
128
What is the first-choice antibiotic for C. difficile infection?
Metronidazole is the first-choice antibiotic for treating C. difficile infection.
129
What is metronidazole?
Metronidazole is an antibiotic and antiprotozoal medication used to treat a variety of infections, including C. difficile.
130
Why is vancomycin held in reserve for C. difficile treatment?
Vancomycin is held in reserve because of concerns about the emergence of Vancomycin-Resistant Enterococci (VRE).
131
What are other more radical treatments for C. difficile?
Other more radical treatments can include a faecal transplant.
132
What is a faecal transplant?
A faecal transplant (or faecal microbiota transplantation, FMT) is a procedure where stool from a healthy donor is transferred to the colon of a patient to restore healthy gut bacteria, often used for recurrent C. difficile infections.
133
How does Vancomycin work at a molecular level?
Vancomycin is hydrophilic (water-loving) and forms hydrogen bonds with the terminal D-Ala-D-Ala sequence of the peptidoglycan precursor.
134
What is a hydrogen bond?
A hydrogen bond is a relatively weak type of attraction between a hydrogen atom (bonded to a very electronegative atom like oxygen or nitrogen) and another nearby electronegative atom.
135
What is the D-Ala-D-Ala sequence?
The D-Ala-D-Ala sequence is the pair of D-alanine amino acids at the very end of the peptide side chain in the bacterial cell wall building blocks.
136
What are the consequences of Vancomycin binding to D-Ala-D-Ala?
This binding prevents the formation of crosslinks between peptide chains and also blocks the release of the disaccharide-peptide unit from its carrier lipid in the cell membrane.
137
What is a carrier lipid in cell wall synthesis?
A carrier lipid is a fatty molecule in the bacterial cell membrane that transports the peptidoglycan building blocks from inside the cell to the outside where the cell wall is built.
138
How does resistance to vancomycin occur primarily?
Resistance to vancomycin occurs mainly through an alteration (change) in the activity of the ligase enzyme that makes the D-Ala-D-Ala peptide.
139
What do Vancomycin Resistant Enterococci (VRE) with the VanA phenotype produce?
VRE bacteria with the VanA phenotype (a specific type of resistance) produce a different enzyme, D-Ala-D-Lactate ligase.
140
What is D-Ala-D-Lactate ligase?
D-Ala-D-Lactate ligase is an altered enzyme in resistant bacteria that joins D-alanine to D-Lactate instead of to another D-alanine.
141
What does this D-Ala-D-Lactate ligase synthesize?
This enzyme synthesizes an ester linkage (D-Ala-D-Lac) instead of the normal amide linkage (D-Ala-D-Ala).
142
What is an ester linkage?
An ester linkage is a type of chemical bond formed between an acid and an alcohol, with the loss of water. (R-CO-O-R')
143
What is an amide linkage?
An amide linkage is a type of chemical bond formed between an acid and an amine, with the loss of water. (R-CO-NH-R')
144
How does the D-Ala-D-Lactate sequence affect vancomycin binding?
The D-Ala-D-Lactate sequence has a 1000-fold reduction in affinity (binding strength) for vancomycin.
145
Can the D-Ala-D-Lactate sequence still be used in cell wall synthesis?
Yes, despite the change, the D-Ala-D-Lactate can still be added to the L-Lysine in the peptide chain and act as a precursor for crosslink formation, allowing the bacteria to build a cell wall.
146
Are altered ligases also found in vancomycin-producing microorganisms?
Yes, similar altered ligases that cause resistance are also produced by the microorganisms that naturally make vancomycin, likely as a self-protection mechanism.
147
What treatment can be used for VRE infections?
Treatment for VRE infections can involve the antibiotic linezolid.
148
What does the diagram on page 46 illustrate about Vancomycin resistance?
The diagram shows how Vancomycin normally binds tightly to the D-Ala-D-Ala end of the peptidoglycan precursor. In resistant bacteria, this end is changed to D-Ala-D-Lactate, which Vancomycin cannot bind to effectively, thus allowing cell wall synthesis to proceed.
149
How is Vancomycin's binding to D-Ala-D-Ala depicted?
Vancomycin is shown fitting snugly around the D-Ala-D-Ala terminus, forming multiple hydrogen bonds (represented by dotted lines), which blocks the transpeptidase enzyme.
150
How is the D-Ala-D-Lactate structure different in the resistant bacteria?
The resistant bacteria have replaced the final D-Alanine's nitrogen atom (part of the amide bond) with an oxygen atom (forming an ester bond with D-Lactate).
151
Why can't Vancomycin bind effectively to D-Ala-D-Lactate?
The change from an NH group (in D-Ala) to an O atom (in D-Lactate) at a key position removes a crucial hydrogen bond donor site, significantly weakening Vancomycin's ability to 'hold on' to the peptide.
152
What does the diagram on page 47 depict regarding cell wall crosslink formation?
The diagram provides an overview of the steps involved in synthesizing and assembling the peptidoglycan cell wall, from basic building blocks in the cytoplasm to the final cross-linked structure outside the cell.
153
Where do the initial steps of peptidoglycan synthesis occur?
The initial steps, like creating the UDP-NAM and UDP-NAG precursors and adding the initial amino acids (H2N-L-Ala-D-Glu-L-Lys), occur in the cytoplasm of the bacterial cell.
154
How are the D-Ala-D-Ala units added?
The D-Ala-D-Ala dipeptide is added to the L-Lys residue to complete the pentapeptide chain.
155
What is the role of the CARRIER LIPID?
The completed NAM-pentapeptide (with NAG attached) is then transferred to a carrier lipid molecule in the cell membrane. This lipid transports the unit across the membrane to the outside.
156
Where is the growing cell wall located?
The growing cell wall is located outside the cell membrane.
157
What happens once the building block is outside the cell membrane?
Once outside, the disaccharide-pentapeptide unit is added to the growing peptidoglycan chain, and then transpeptidase enzymes create cross-links with other chains.
158
What is the main process shown in the diagram on page 48?
The diagram on page 48 illustrates the enzymatic process of forming peptide cross-links between adjacent peptidoglycan strands in the bacterial cell wall.
159
What is released when the transpeptidase enzyme forms a crosslink?
The terminal D-Alanine residue is released from one of the peptide chains during the crosslinking reaction.
160
What is Daptomycin (Cubicin)?
Daptomycin (brand name Cubicin) is a lipopeptide antibiotic.
161
What is a lipopeptide?
A lipopeptide is a molecule that has a lipid (fatty) part and a peptide (short chain of amino acids) part.
162
When was Daptomycin approved by the FDA for complicated skin infections (SSSI) caused by MRSA?
Daptomycin was approved by the FDA in 2003 for treating complicated skin and skin structure infections (SSSI) caused by MRSA.
163
What are complicated skin and skin structure infections (SSSI)?
SSSIs are bacterial infections of the skin and underlying tissues that are more severe or extensive than simple skin infections and may require hospitalization or surgery.
164
What new indication was Daptomycin approved for by the FDA in 2006?
In 2006, the FDA approved daptomycin for treating S. aureus bacteraemia (bloodstream infection) due to MRSA, including right-sided endocarditis.
165
What is right-sided endocarditis?
Right-sided endocarditis is an infection of the inner lining of the heart chambers and valves on the right side of the heart.
166
Why can't Daptomycin be used to treat pneumonia?
Daptomycin cannot be used to treat pneumonia because it binds strongly to pulmonary surfactant (a substance in the lungs), making it inactive.
167
What is pulmonary surfactant?
Pulmonary surfactant is a complex substance lining the air sacs (alveoli) in the lungs that reduces surface tension and prevents the air sacs from collapsing.
168
Where was Daptomycin originally isolated from?
Daptomycin was originally isolated by Eli Lilly and Co. from a strain of Streptomyces roseosporus found in a soil sample from Mount Ararat in Turkey.
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What is Streptomyces roseosporus?
Streptomyces roseosporus is a species of bacteria belonging to the Streptomyces genus, known for producing various bioactive compounds, including daptomycin.
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What is a depsipeptide?
A depsipeptide is a peptide (chain of amino acids) in which at least one of the normal amide (CONH) bonds has been replaced by an ester (COO) link.
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How is the structure of Daptomycin described in terms of its amino acids and ring?
In Daptomycin, 10 of its 13 amino acids form a depsipeptide ring, with the other 3 amino acids attached to this ring through a threonine residue.
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What is threonine?
Threonine is one of the essential amino acids, the building blocks of proteins.
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What is essential for Daptomycin's rapid bactericidal activity against Gram positive bacteria?
Calcium ions (Ca2+) are essential for Daptomycin to quickly kill Gram positive bacteria.
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How is Daptomycin believed to begin its mode of action?
Its mode of action is thought to involve the insertion of Daptomycin into the bacterial cell's lipid bilayer (cell membrane).
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What is a lipid bilayer?
A lipid bilayer is the fundamental structure of a cell membrane, composed of two layers of lipid (fatty) molecules.
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What facilitates Daptomycin's insertion into the lipid bilayer?
The insertion is helped by Daptomycin's lipid tail, which promotes weak hydrophobic (water-repelling) interactions with the phospholipid bilayer.
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What are hydrophobic interactions?
Hydrophobic interactions are the tendency of nonpolar (water-repelling) molecules or parts of molecules to group together when in a watery environment.
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What is a phospholipid bilayer?
A phospholipid bilayer is a type of lipid bilayer where the lipids are phospholipids, which have a water-loving (hydrophilic) head and a water-repelling (hydrophobic) tail.
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What does the interaction of daptomycin, calcium, and phosphatidyl glycerol promote?
This interaction promotes mild disturbances in the lipid membrane and causes the contents of the bacterial cell to leak out.
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What is phosphatidyl glycerol?
Phosphatidyl glycerol is a type of phospholipid found in bacterial cell membranes, and it plays a role in Daptomycin's action.
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How does Daptomycin's interaction with the cytoplasmic membrane affect it?
Its interaction with the cytoplasmic (cell) membrane alters the membrane's permeability, meaning it changes what can pass in and out of the cell.
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What is Daptomycin oligomerisation?
Daptomycin oligomerisation is when multiple daptomycin molecules group together to form a larger complex.
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What promotes Daptomycin oligomerisation?
Binding to calcium ions (Ca2+) promotes this oligomerisation.
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What does Daptomycin oligomerisation create in the membrane?
This grouping creates a large pore (hole) in the bacterial cell membrane.
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What are the consequences of this pore formation?
The pore allows potassium ions (K+, essential for the cell) to leak out (efflux), causes membrane depolarization (loss of electrical charge difference across the membrane), and eventually leads to cell death.
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What is potassium efflux?
Potassium efflux means that potassium ions are flowing out of the cell.
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What is membrane depolarization?
Membrane depolarization is a decrease in the difference in electrical potential (voltage) across a cell membrane.
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What genetic changes are linked to resistance to Daptomycin?
Resistance to Daptomycin is linked to point mutations (small changes) in the mprF and yycG genes.
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What is a point mutation?
A point mutation is a change in a single nucleotide base pair in the DNA sequence.
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What does the mprF enzyme do?
The mprF enzyme influences the nature of the phospholipid content of the cell membrane; specifically, it helps add lysine (an amino acid) to membrane phosphatidylglycerol.
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What is the yycG gene believed to be involved in?
The yycG gene is thought to be involved in controlling cell permeability.
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With what other resistance are cases of Daptomycin non-susceptible S. aureus often associated?
Cases of S. aureus that are not susceptible to daptomycin are often associated with strains that are also unresponsive to vancomycin (VRSA or VISA).
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What are VRSA and VISA?
VRSA stands for Vancomycin-Resistant S. aureus, and VISA stands for Vancomycin-Intermediate S. aureus (meaning it's partially resistant).
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How do VRSA/VISA strains exhibit Daptomycin resistance?
These strains often have thickened cell walls, and daptomycin resistance is thought to be due to its inability to diffuse (pass) through these thicker cell walls to reach its target at the lipid membrane.
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Is Daptomycin resistance common?
Daptomycin resistance is still considered rare.
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Are there programs to monitor Daptomycin activity?
Yes, there are established daptomycin surveillance programs around the world that monitor its in vitro (in the lab) activity against bacteria.
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Where was a Daptomycin-resistant Paenibacillus strain found?
A strain of Paenibacillus sp. (LC231) with daptomycin resistance was found in Lechuguilla Cave.
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What is Paenibacillus?
Paenibacillus is a genus of bacteria, some species of which can be found in soil and other environments.
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How long had this cave been isolated from the surface?
This cave has been isolated from the surface for over 4 million years, suggesting resistance mechanisms can evolve naturally even without human antibiotic use.
200
What does the diagram on page 54 reiterate about the sites of action for different antibiotics?
This diagram is a repeat of the one on page 11, showing a bacterial cell and indicating where various classes of antibiotics exert their effects.
201
Where do β-LACTAMS and VANCOMYCIN act?
They act on the cell wall of the bacteria.
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Where does ISONIAZID act?
It acts on the cell membrane of the bacteria.
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Where do QUINOLONES act?
They act on the DNA inside the bacterial cell.
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Where do SULPHONAMIDES act?
They act in the cytoplasm, interfering with metabolic processes.
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Where do CHLORAMPHENICOL, TETRACYCLINES, and MACROLIDES act?
They act on the ribosomes, preventing protein synthesis.
206
When was Nalidixic acid discovered?
Nalidixic acid was discovered in 1962.
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How was Nalidixic acid discovered?
It was discovered as a byproduct during the synthesis and purification of chloroquine, an anti-malarial drug.
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What is chloroquine?
Chloroquine is a medication primarily used to prevent and treat malaria.
209
What is the antibacterial activity of first-generation quinolones like Nalidixic acid?
Nalidixic acid and other first-generation quinolones have weak anti-bacterial (bactericidal) activity.
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What are first-generation quinolones primarily used to treat?
First-generation quinolones are only used to treat urinary tract infections (UTIs).
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How well are quinolones absorbed orally?
All quinolones are generally well absorbed when taken orally (by mouth).
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Are quinolones highly serum-protein bound?
Yes, they are usually highly bound to proteins in the blood serum.
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What does serum-protein bound mean?
Serum-protein bound means that a drug attaches to proteins in the blood, which can affect how much of the drug is free to act on its target and how long it stays in the body.
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What is the effect of high serum-protein binding on quinolones' half-lives?
This high binding gives them long half-lives (they stay in the body for a longer time).
215
What is a drug's half-life?
A drug's half-life is the time it takes for the concentration of the drug in the body to reduce by half.
216
Why are quinolones often used in high doses?
They are used in high doses due to this protein binding (which reduces the amount of free, active drug) and their relatively weak activity (for first-generation ones).
217
What are some side-effects of quinolones?
Side-effects include GI disturbance, rashes, prolongation of the QT interval (heart rhythm issue), fatigue, dizziness, visual disturbances, convulsions (especially with NSAIDs), and spontaneous tendon ruptures.
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What is prolongation of the QT interval?
Prolongation of the QT interval is an abnormality of the heart's electrical activity seen on an electrocardiogram (ECG), which can increase the risk of dangerous heart rhythms.
219
What are NSAIDs?
NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) are common pain relievers and anti-inflammatory drugs, like ibuprofen and naproxen.
220
How did later generations of quinolones improve?
Later generations have a broader spectrum of activity (they work against more types of bacteria).
221
What structural modification contributed to this broader spectrum?
This improvement was mostly due to the introduction of a fluorine atom at the 6-position of the quinolone structure.
222
How many generations of quinolones are there now?
There are now 2nd, 3rd, and 4th generation quinolones.
223
What does the diagram on page 56 show?
The diagram shows the chemical structures of different generations of quinolone antibacterials, starting with Nalidixic acid (1st generation) and progressing to newer ones like Ciprofloxacin (2nd gen), Levofloxacin (3rd gen), and Moxifloxacin (4th gen).
224
What is a common structural feature in all quinolones shown?
All quinolones shown have a core bicyclic (two-ring) structure with a nitrogen atom and a carboxylic acid group (−COOH) at specific positions.
225
How does the structure of Ciprofloxacin differ from Nalidixic acid?
Ciprofloxacin (a fluoroquinolone) has a fluorine atom and a piperazine ring added to the basic nalidixic acid structure, which enhances its activity.
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What is a piperazine ring?
A piperazine ring is a six-membered heterocyclic ring containing two nitrogen atoms at opposite positions.
227
What are Levofloxacin and Moxifloxacin examples of?
Levofloxacin and Moxifloxacin are examples of later-generation fluoroquinolones with even broader spectrums of activity and different side groups.
228
Are quinolones bactericidal or bacteriostatic?
Quinolones are bactericidal, meaning they kill bacteria.
229
What bacterial enzymes do quinolones inhibit?
They inhibit two important bacterial enzymes: DNA gyrase and topoisomerase IV.
230
What is topoisomerase IV?
Topoisomerase IV is an enzyme in bacteria, similar to DNA gyrase, that helps to untangle and separate newly copied circular DNA daughter chromosomes during cell division.
231
Why do positive supercoils form in DNA during replication?
DNA is a right-handed helix, so when the strands are unwound for replication, the DNA ahead of the replication site gets overwound, forming positive supercoils (knots).
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What are supercoils in DNA?
Supercoils are extra twists in the DNA double helix, like coiling an already coiled rope. They can be positive (overwinding) or negative (underwinding).
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What must happen for DNA replication to proceed?
For DNA replication to continue, these positive supercoils must be removed by enzymes like DNA gyrase or topoisomerase IV, which relax the DNA chain.
234
How do these enzymes remove positive supercoils?
They remove positive supercoils by introducing negative supercoils, resulting in a tension-free DNA double helix.
235
How do DNA gyrase and topoisomerase IV mechanically relax bacterial DNA?
These enzymes relax DNA by cutting one or both strands of the DNA, passing another part of the DNA strand(s) through the cut, and then resealing the cut.
236
How do quinolones interfere with these enzymes?
Quinolones bind to these enzymes (gyrase and topoisomerase IV), preventing them from relaxing the DNA helix.
237
What is the consequence of preventing DNA relaxation?
Preventing DNA relaxation stops DNA replication, as the DNA cannot be properly unwound and copied.
238
Which enzyme do quinolones primarily target in Gram negative bacteria?
In Gram negative bacteria, quinolones primarily target DNA gyrase.
239
Which enzyme do quinolones primarily target in Gram positive bacteria?
In Gram positive bacteria, quinolones primarily target topoisomerase IV.
240
Do mammalian cells have DNA gyrase or topoisomerase IV?
No, mammalian (human) cells do not have DNA gyrase or topoisomerase IV.
241
Do mammalian cells have topoisomerases?
Yes, mammalian cells do have different types of topoisomerases (topoisomerases I and II), but quinolones do not bind effectively to these human enzymes.
242
How does this difference contribute to selectivity?
This difference in enzymes is why quinolones have some selectivity, meaning they are more harmful to bacteria than to human cells.
243
How does the difference in enzymes contribute to selectivity?
This difference in enzymes is why quinolones have some selectivity, meaning they are more harmful to bacteria than to human cells.
244
What does inhibition of DNA gyrase and topoisomerase IV lead to in bacteria?
Inhibition of these enzymes leads to cell death, especially if the bacterial cell is also dealing with other toxic effects of the quinolones at the same time.
245
What are the two major mechanisms by which bacteria develop resistance to quinolones?
Resistance arises through two main ways: 1) alterations (changes) in the target enzymes (DNA gyrase or topoisomerase IV), and 2) decreased accumulation of the quinolones inside the bacterial cell.
246
How can decreased accumulation of quinolones occur?
Decreased accumulation can happen due to the membrane becoming less permeable to the drug or due to the over-expression (making too many) of efflux pumps that pump the drug out.
247
How do alterations to DNA gyrase occur?
Alterations to DNA gyrase happen via mutations in the quinolone-resistance determining region (QRDR) of the gyrA gene.
248
What is the quinolone-resistance determining region (QRDR)?
The QRDR is a specific part of the gene coding for DNA gyrase (or topoisomerase IV) where mutations often occur that lead to quinolone resistance.
249
What does the gyrA gene encode?
The gyrA gene encodes the two A subunits of the DNA gyrase enzyme (which is a tetrameric enzyme, meaning it has four subunits in total).
250
What does the gyrB gene encode?
The gyrB gene encodes the two B subunits of the DNA gyrase enzyme.
251
Have similar mutations been found in topoisomerase IV?
Yes, similar mutations have been described in topoisomerase IV that decrease quinolone binding and cause resistance.
252
How do quinolones cross the outer membrane of bacteria?
Quinolones cross the outer membrane via specific protein channels called porins (for all quinolones) or by diffusing through the phospholipid bilayer itself (only for hydrophobic, or water-repelling, quinolones).
253
What are porins?
Porins are protein channels embedded in the outer membrane of Gram-negative bacteria (and some other bacteria) that allow passive diffusion of small, specific molecules like nutrients and some antibiotics into the cell.
254
How does the outer membrane of P. aeruginosa contribute to its intrinsic resistance to quinolones?
The outer membrane of P. aeruginosa has very low permeability to small hydrophobic molecules, giving this bacterium a natural (intrinsic) resistance to quinolones.
255
How many main porins does E. coli have?
E. coli has three main porins.
256
What is associated with increased quinolone resistance in E. coli regarding porins?
A decrease in the level of one of these porins, called OmpF, is associated with an increase in resistance to quinolones in E. coli.
257
What is OmpF?
OmpF is a type of porin protein found in the outer membrane of E. coli and other Gram-negative bacteria, involved in the uptake of various substances.
258
Which bacteria exhibit well-characterised efflux pumps for quinolones?
Both P. aeruginosa (Gram negative) and S. aureus (Gram positive) show well-studied efflux pumps that can pump quinolones out of the cell.
259
What is Bacillus anthracis the causative agent of?
Bacillus anthracis is the bacterium that causes the disease anthrax.
260
What are the characteristics of B. anthracis?
B. anthracis is a Gram positive, spore-forming, rod-shaped bacterium.
261
Where is B. anthracis commonly found?
It is commonly found in the soil of grazing areas for animals.
262
How many cases of anthrax were there in NSW in approximately 40 years?
There were only 3 cases of anthrax in New South Wales (NSW), Australia, in about 40 years.
263
How else has B. anthracis been used?
It has also been used as a biological warfare agent.
264
What event involving anthrax spores occurred in the US in 2001?
In September/November 2001, anthrax spores were sent in the US mail, leading to 22 cases of anthrax and 5 deaths.
265
What is the prognosis for cutaneous anthrax?
Patients with cutaneous (skin) anthrax can usually be completely cured with treatment.
266
What is cutaneous anthrax?
Cutaneous anthrax is a form of anthrax infection that affects the skin, typically causing a black sore.
267
What is the prognosis for intestinal and inhalational (pulmonary) anthrax?
Intestinal anthrax (from eating contaminated meat) and inhalational (pulmonary) anthrax (from breathing in spores) have very high mortality (death) rates.
268
Is there vaccine availability for anthrax in Australia?
Vaccine availability for anthrax is limited in Australia.
269
What does treatment for anthrax usually involve?
Treatment usually involves antibiotics like ciprofloxacin or doxycycline.
