Antimicrobials and Resistance Flashcards
(105 cards)
1
Q
What are the characteristics of bacterial disease?
A
- Associated with bacterial growth: physical/mechanical effects and intracellular multiplication, leading to cell lysis.
- Immunopathology: inflammatory response to bacterial products and bacterial endotoxins
- Associated with bacterial secretions, such as bacterial exotoxins
- Hosts inappropriate response to bacteria
2
Q
Describe the structure and properties of bacterial endotoxins.
A
- Structural components is released with organism dies
- Heat stable, intrinsically poorly antigenic
3
Q
Describe the action of bacterial endotoxins.
A
Over activates complement cascade, causing:
- High fever
- Severe fluid loss from blood system, leading to vascular collapse
- IV coagulation then organ haemorrhaging
- Septicaemia/endotoxic shock and death
4
Q
Why are antimicrobials used?
A
To prevent bacteria multiplying and shedding components. Bacteriostatic to prevent growing.
5
Q
What are the properties of bacterial exotoxins?
A
- Actively secreted proteins
- Specific activity
- Heat labile
- Antigenic
6
Q
What are the factors that facilitate entry, invasion and survival?
A
Mucinase
Collagenase
Urease
Leukocidins
7
Q
What is the function and structure of bactericidal drugs?
A
Bactericidal to prevent bacteria producing toxins.
AB subunit structure (A=activity / B=binding):
- Decreased protein synthesis
- Decreased nerve synapse function
- Membranes damaged, physically or functionally
Such as neurotoxins, cytotoxins and enterotoxins.
8
Q
What are the uses of antimicrobial agents?
A
Antimicrobial agents inhibit/kill microorganisms.
99% unsuitable for treatment of infectious diseases as they are too toxic for the host, such as disinfectants and antiseptics.
1% suitable for treatment, such as chemotherapeutic agents.
9
Q
Distinguish natural and synthetic chemotherapeutic agents.
A
Naturally produced CTAs are antibiotics, metabolic biproducts of certain bacteria/fungi.
Synthetic CTAs are either totally man made or modified from antibiotics to improve activity and pharmacological properties, such as penicillin, ampicillin and carbenicillin.
10
Q
What makes a successful chemotherapeutic agent?
A
Its selective toxicity, such as toxicity to prokaryotes being greater than toxicity to eukaryotes.
11
Q
Define therapeutic dose.
A
The level of CTA needed for clinical treatment of an infection in a specific host.
12
Q
Define toxic dose.
A
Level of the same CTA which is too toxic for use in that host.
13
Q
What is the therapeutic index?
A
Therapeutic index = toxic dose / therapeutic dose
High index = selectively toxic, useful
Low index = tox to host, side effects
14
Q
Distinguish bacteriostatic and bactericidal chemotherapeutic agents.
A
Bacteriostatic - inhibit bacterial growth and multiplication but rely on the host’s immune system to remove the bugs.
Bactericidal - rapidly lethal to the bacterial in their own right.
15
Q
How are bacteriostatic chemotherapeutic agents given?
A
It is therefore essential to give the full course of such agents to allow sufficient time for the immune system to complete its job whilst preventing regrowth of the bacterial population.
It is contraindicated to use these CTAs in immunosuppressed patients.
16
Q
What are 3 examples of agents that may be bacteriostatic and bactericidal, dependent on condition?
A
- Chloramphenicol kills H.influenza but only inhibits E.coli
- Erythromycin is bacteriostatic at normal concentrations but bactericidal at higher levels
- Penicillin is bactericidal against rapidly growing organisms but ineffective against those in stationary phase
17
Q
Distinguish broad and narrow range chemotherapeutic agents.
A
Broad range CTAs – effective against many different bacterial types.
Narrow range CTAs – affect limited groups, such as gram negatives or certain genera only.
Start broad and get narrower once we have a better identification of the bacteria present and the conditions.
18
Q
What are the mechanisms of CTAs?
A
- Inhibiting peptidoglycan cell wall
- Inhibiting protein synthesis
- Inhibiting nucleic acid synthesis
- Impairing membrane functions
19
Q
What are the stages of inhibiting the peptidoglycan cell wall?
A
- Precursors
- Subunits
- Lipid carrier
- Growing peptidoglycan molecule
Affects only actively growing bacteria, bactericidal and selectively toxic.
20
Q
What are the CTAs that inhibit protein synthesis?
A
Some are bactericidal and some are bacteriostatic, but are all selectively toxic.
21
Q
What are the CTAs that inhibit nucleic acid synthesis?
A
Bactericidal and bacteriostatic, some are selectively toxic.
22
Q
What are the CTAs that impair membrane function?
A
Eukaryotic and prokaryotic share features so few are selectively toxic, but are bactericidal.
23
Q
What is metabolic antagonism of CTAs?
A
- CTAs are structural but not functional analogues of bacterial growth factors
- Bactericidal
- Selectively toxic
24
Q
What are the mechanisms of bacterial resistance?
A
- Production of enzymes – attack CTA prevent activity or degrade CTA
- Modify CTAs target – as produced or after production. Must be a sublethal change
- Alter CTA uptake/retention – no entry to cell, upregulate removal more than uptake
- Upregulate target production – dilute out effect of CTA
- Modify metabolic pathways – alternative pathway to the same end point
- Cross resistance
25
What is cross resistance by ESBLs?
ESBLs, extended spectrum beta lactamases – produced by enterobacteria, but are secreted so will target penicillins/cephalosporins which are used to target MRSA for example. Resistance occurs and is effective in non-target organisms.
26
How can cross resistance be treated?
Can be treated by using agents such as clavulanic acid (a suicide inhibitor) which inhibits beta lactamases in combination (such as coamoxiclav).
27
What are metallo beta lactamases?
Resistant to inhibitors such as clavulanic acid.
28
How can bacterial resistance arise to a CTAs?
Intrinsically resistant, or being intrinsically sensitive but still developing resistance via spontaneous mutation or recombination.
29
How does spontaneous mutation cause CTA resistance?
- Under normal conditions there is no advantage. CTA resistance lost by overgrowth by sensitive bacteria.
- During treatment there is clear advantage. Resistance clone selected.
30
How does recombination lead to CTA resistance?
- Transformation
- Transduction
- Conjugation
31
What is the importance of recombination causing CTA resistance?
1. Negates therapy – individuals/outbreaks
2. Resistance arising in commensals may lead to pathogens
3. Zoonoses pass resistance from animals to humans
32
What are the veterinary aims regarding CTAs?
- CTA development
- Restrict CTA use in therapy and in growth promotion
- Test pathogen sensitivity
- Use correct dose, avoiding toxicity in the rest of the body
- Use dual therapy, attacking different sites on the bacteria at once to prevent resistance
33
What is the structure of a virus?
- Lipoprotein envelope
- Nucleic acid core and capsid make up the nucleocapsid
- Capsomere - the morphological protein units of the coat
34
Give a brief description of the process of viral replication.
1. Attachment to plasma membrane
2. Entry into cytoplasm and nucleus
3. Uncoating of virus particle
4. Synthesis of mRNA and protein
5. Assembly of virus particles
6. Exit from cell
35
Give the process of the lifecycle of a retrovirus.
1. Retrovirus will bind to cell surface, often involving interacting with specific proteins.
2. Fusion of the virus with the cell membrane and virus can then gain entry into the cytoplasm.
3. Uncoating of the virus and reverse transcription. This leads to the production of DNA.
4. DNA can then be integrated into the host cell DNA.
5. Transcription of mRNA.
6. mRNA converted to protein.
7. New genetic material along with protein can be assembled into a new viral particle.
8. New viral particle released into the extracellular space.
9. Viral particles mature and repeat process at a new host cell.
36
What are the potential drug targets in viruses?
Attachment
Penetration
Uncoating
Multiplication of genetic material
Protein synthesis
Assembly
Release
37
Why are there few antiviral drugs available in both human and veterinary medicine?
- Viruses replicate genome I different ways, therefore not all antivirals will work for every drug
- Viral latency
- Viruses do not produce protein making machinery and instead use host cell machinery. Drugs that interfere with such pathways are likely to have effects on the host cells.
- Viruses may not encode many surface proteins for drugs to attach to (as they have a small genome).
- Viruses replicate by hijacking host cells and using their machinery to replicate (they are very small). So if a drug is going to kill a virus, it will also be killing host cells which they have hijacked.
- Some viruses are host specific, thus targeting specific receptors which might be unique to the species. Drugs that interfere with such interaction have to account for this.
- A lot of viral replication phases are intracellular, meaning it may be hard o target these phases without also damaging the host cell.
38
How are viruses targeted via viral attachment?
- Most effective preventative step, which stops virus attaching to host cells
- Is done by immunisation – antibodies against viral proteins to prevent attachment
- Interferons are sometime useful
39
Describe the action of amantadine.
- Inhibits penetration and uncoating of influenza A virus in humans.
- Has been used to prophylactically in humans when facing epidemic to control spread.
- Experimentally used in control of influenza in horses and turkeys
- Some drug also has analgesic actions via inhibiting NMDA glutamate receptor – sometimes used in animals unresponsive to other analgesics, such as opioids.
40
What are the 3 sets of drugs used to inhibit viral multiplication? How do they work?
- Idoxuridine and related and compounds
- Acyclovir and related compounds
- Zidovudine/azidothymidine
These are all nucleoside analogues, resemble the structures of specific nucelosides so they can interfere with the formation of double stranded DNA and the base pairing between them.
41
Which drugs have very similar structures to deoxyuridine?
Trifluridine and idoxuridine have very similar structures to deoxyuridine but with halogens groups attached, which changes the shape and charge of the molecule.
42
How do trifluridine and idoxuridine work?
- Trifluridine and idoxuridine can be incorporated into viral DNA
- Trifluridine iodine groups prevent base pairing
- This therefore inhibits DNA replication – mainly affective against herpes virus
- Inhibits mammalian DNA replication, therefore not given systematically. Only be used topically
- Not licensed for vet use
- Used only topically – herpetic keratitis
43
How does acyclovir work?
- Structurally related to guanosine
- Is a pro-drug – not active on its own and must be activated to have an antiviral effect
- Inactive until phosphorylated by kinases – activated about 3 times
- First phosphorylation more efficiently carried out by viral thymidine kinase, then host kinases phosphorylate. Then the host cell kinases will carry out the last 2 phosphorylation events.
44
What is acyclovir used for?
- Acyclovir-triphosphate is a DNA polymerase inhibitor
- DNA polymerase assembles and viral replication is inhibited
- Used for herpes infections, available as ophthalmic ointment, skin ointment, tablet and injection.
- Not licensed for vet use
45
What 2 drugs are similar to acyclovir?
Ganciclovir and famciclovir are both similar to acyclovir, as prodrugs activated by viral kinases and then host kinases.
46
Describe the action of vidarabine.
- Analogue of adenosine
- DNA polymerase inhibitor
- Inhibits viral and host cell enzyme, viral being 20 fold more sensitive
- Used for herpes infections, available as topical eye treatment available
47
What is a retrovirus?
A retrovirus contains RNA not DNA. Reverse transcriptase converts RNA to DNA. DNA incorporated in host cell genome. Host cell produces new copies of virus.
48
How does zidovudine/azidothymidine work?
- Zidovudine is a reverse transcriptase inhibitor, preventing the production of DNA.
- At high doses it will inhibit DNA polymerase
- Zidovudine is a prodrug – activated by host cell kinases
- Triphosphate produced by host kinases
49
What can zidovudine/azidothymidine be used for?
Treatment of FIV positive cats – may increase survival time and quality of life.
- Can cause hepatotoxicity and anaemia
- Contraindicated in cats with renal or hepatic impairment
- Not licensed for vet use
50
What is the use and mechanism of action of Virbagen Omega?
- Recombinant feline omega interferon
- Licensed for use in cats and dogs
- Dogs: treatment of parvovirus, up to 6.4 fold decrease in mortality
- Cats: treatment of FeLV and FIV, 20-30% reduction in mortality
- Mechanism of action is to stimulate anti-viral processes so virus is destroyed by host body
51
What are the possible drug targets for future therapies?
- Drugs that are chemokine receptor antagonists that will block the chemokine receptor and prevent the virus from being able to bind.
- Integrases insert viral DNA into the host cell DNA, so we can have drugs that inhibit these integrases.
- Inhibitors of proteases to prevent new viral proteins
- Inhibiting protein synthesis is not effective way to target viruses, due to difficulty of targeting
- Drugs that inhibit budding and release of new viral particles
52
What are the commonly used antiviral drugs in small animal practice?
Acyclovir*
Famciclovir*
Zidovudine*
Interferon omega
*=not licensed for vet use
53
What are the rarely used antiviral drugs in small animal practice?
Trifluridine*
*= not licensed for vet use
54
What are the commonly used antiviral drugs in farm animal practice?
Tylvalosin
55
What are the rarely used antiviral drugs used in farm animal practice?
Amantadine*
*= not licensed for vet use
56
What are the commonly used antiviral drugs in equine practice?
Acyclovir*
*= not licensed for vet use
57
What are the rarely used antiviral drugs used in equine practice?
Amantadine*
Ganciclovir*
Trifluridine*
Vidarabine*
Interferon alpha*
*= not licensed for vet use
58
What are class I reactions in bacteria?
All cells including bacteria, take in basic precursors and combine them to make precursor molecules and ATP. These are class I reactions. Makes them not good drug targets, as the same sort of reactions and molecules are present in all sorts of cells.
59
What are class II reactions in bacteria?
Precursor molecules and ATP can be combined to create more complex molecules, such as hexosamines, amino acids and nucleotides. Going on in many cells, eukaryotic, bacteria and mammalian cells so not often the target of antibacterial drugs, though there are some drugs that will selectively target certain molecules in bacteria. . These are class II reactions.
60
What are class III reactions in bacteria?
End stage molecules, such as peptidoglycan, proteins, RNA and DNA, are produced in class III reactions. These are more complicated reactions and do differ between eukaryotic and bacterial cells. Peptidoglycan for example is only produced in bacteria so this synthesis can be targeted. Protein synthesis is similar in each but involve different enzymes, so dugs can selectively target these.
61
How do antiviral and antibacterial drugs differ?
Unlike antiviral drugs, there are many antibacterial drugs and many targets to be used.
62
What are major drug targets for antibacterial drugs?
- Cell wall synthesis – mammalian cells do not have a cell wall so penicillins, cephalosporins, glycopeptides, carbapenems and monobactams can be used to target cell wall synthesis and have no effect on mammalian cells.
- Protein synthesis – selectively targets bacterial protein synthases, such as macrolides, chloramphenicol, clindamycin, aminoglycosides and tetracyclines.
- Folic acid metabolism – a class II reaction, used as precursors to form things like DNA. Can be selectively targeted in bacteria without affecting mammalian cells. Drugs are sulphonamides and trimethoprim.
- DNA gyrase – quinolones can target this enzyme.
- DNA directed RNA polymerase – rifampicin will target this enzyme
63
Distinguish gram positive and gram negative bacteria.
Gram positive has a thick cell wall, that is 50% peptidoglycan with no outer membrane.
Gram negative has a thin cell wall that is 5% peptidoglycan with an outer membrane that constructs antibacterial entry.
64
Describe the structure of peptidoglycan.
Polymer made of N-acetylmuramic acid and N-acetylglucosamine amino sugars. Have tetrapeptide side chains with peptide cross links attached, which links together different amino sugar chains.
65
What is the effect of beta lactams on peptidoglycan?
Prevent the cross-linking peptides from binding to the tetrapeptide side chains. Beta lactams target the synthesis of these peptidoglycan structures and prevent the cross linking of the amino sugar chains. Cell wall structure and bacteria’s integrity is compromised.
66
What are the 2 beta lactam antibiotics?
Penicillin
Cephalosporin
67
What are transpeptidases and their effect with beta lactam drugs?
Ability to bind penicillin binding proteins, transpeptidases, which are responsible for the last step of cross linking sugar chains. What transpeptidases are present and mutations in transpeptidases determine the action of beta lactam drug and may reduce effectiveness. Whether the drug has access to transpeptidase – gram negative bacteria LPS can hinder drug passage. Stability against beta lactamase activity also determines the effectiveness of beta lactams.
68
What are the properties of beta lactams?
- Beta lactam ring is at the centre of beta lactam antibiotics. If this ring is lost, the effectiveness of the antibacterial is lost.
- Diverse group of enzymes
- Different bacteria produce different beta lactamases
- Staphylococcal beta lactamase called penicillinase
- These break the beta lactam ring by breaking the carbon-nitrogen bond and the penicillin drug in activated.
69
What is clavulanic acid?
- Beta lactamase inhibitor
- No antibacterial effect alone
- Can be administered with beta lactam antibiotic
70
What is synulox?
A 1:1 of clavulanic acid and amoxicillin.
71
Describe benzylpenicillin.
- First penicillin – penicillin G
- Acid instable – the drug is not orally active and is broken down in the stomach
- Narrow spectrum of activity – gram positive and cocci
- Broken down by beta lactamase
72
What are the advantages of semi-synthetic penicillins?
- Increased stability to acids
- Decreased susceptibility to beta lactamase
- Increased activity against gram negative bacteria
73
What are the 3 key penicillins and their properties?
Benzylpenicillin = poor acid stability, susceptible to beta lactamase, G+ cocci spectrum
Ampicillin = medium acid stability, susceptible to beta lactamase, as for bzpen and G- spectrum
Amoxicillin = very good acid stability, susceptible to beta lactamase, as for bzpen and G- spectrum
74
How is ribosome variation a drug target?
80S eukaryotic cells (mammalian host cell) – 60S and 40S subunits
70S eukaryotic and prokaryotic cells (mitochondria and bacteria) – 50S and 30S sub units
75
Which drugs target each stage of bacterial protein synthesis?
- Competition with tRNA for the A site – tetracyclines, such as doxycycline, prevent the tRNA from binding
- Misreading of message – aminoglycosides, such as streptomycin, cause wrong tRNA to bind
- Prevent peptide bond formation – chloramphenicol and florfenicol
- Inhibition of translocation of ribosome complex along mRNA – macrolides, such as erythromycin
76
What do sulphonamides and trimethoprim target?
Bacterial folate synthesis:
- Mammals do not synthesise folate and so get this from the diet. So sulphonamides can be used to target dihydropteroate synthetase in bacteria.
- Sulphonamides therefore inly affect bacterial cells
- Bacteria dihydrofolate reductase is more sensitive to trimethoprim than the mammalian form
77
What are the genetic determinants of antibiotic resistance?
- Chromosomal determinants – mutations
- Extrachromosomal determinants – plasmids
- Transfer of genes between genetic elements within the bacteria – transposons
- Transfer of genes between bacteria – transformation, conjugation and transduction
78
What are the mechanisms of antibiotic resistance?
- Inactivation of the antibacterial drug
- Alternation of the target site
- Decrease drug accumulation in the bacterium
- Upregulate synthesis of target
- Alter metabolic pathway
79
Describe how beta lactamase is inactivated?
- Use of clavulanic acid may limit this
- Resistant to 1 penicillin, resistant to many
- Cross resistance between penicillins and cephalosporins not complete
- May be encoded on plasmids or chromosome
- Chromosome – expression inducible
- Plasmid – constitutively produced
80
How are drug binding sites altered?
- Mutations in proteins
- Erythromycin resistance – mutation in 50S ribosome subunit
- Quinolones – mutation in DNA gyrase
81
What do tetracyclines do?
Decrease drug accumulation
82
What can be done in veterinary practice?
- Use of antimicrobials at an early stage
- Use of narrow spectrum drug wherever possible
- Use appropriate dose and duration of treatment
- Emphasise to clients need to follow product labelling
- Perform sensitivity testing on causal bacteria wherever possible
- If treatment does not work, report to VMD
83
What are 3 types of use of antiomicrobials in veterinary practice?
Prophylactic use – prevention of infection, such as after surgery
Metaphylactic use – individuals at risk of infection, in infected/contaminated environment
Therapeutic use – treatment of present infections
84
What were antimicrobials previously used as?
Growth premoters.
Mechanism: “regulatory effect” on gut microflora. Feed conversion more efficient (more kg’s growth per kg of feed)
85
What is underdosing?
- Insufficient amount administered – e.g. weight estimation incorrect
- Course not completed – concentration lowers below therapeutic level with harmful microorganism still present
- Sensitive organisms will die, resistant organisms survive so there is selection for more resistant organisms
86
What is antimicrobial resistance?
Microorganisms are resistant to an antimicrobial if they are no longer killed or inhibited at therapeutic concentrations of that antimicrobial – clinical resistance.
All resistance is genetic – part of organisms genome and transferable between microorganisms.
87
Name 4 mechanisms of resistance.
Intrinsic resistance
Acquired resistance
Chromosomal resistance
Transferable resistance
88
What is intrinsic resistance?
Organism lacks cellular mechanism that antimicrobial attacks, or the cell wall is impermeable.
89
What is acquired resistance?
Through mutation in the genome and through transfer from other microorganisms.
90
What is chromosomal resistance?
Mutation. Transferred genetically and/or clonally to all offspring of microorganism.
91
What is transferable resistance?
- Certain genes can move between chromosomal DNA and extrachromosomal DNA
- Plasmids transferrable between (different species of) bacteria
- Transposons – short DNA sequences that move between plasmids, between plasmids and chromosomes, plasmids and bacteriophages
- Integrons – naturally occurring gene expression elements – gene cassettes
92
How can resistance be transferred?
Conjugation – plasmatic bridge between cells
Transduction – transmitted through bacteriophages
Transformation – uptake of free DNA after cell lysis
93
Distinguish occupational and hospital risk.
Occupational risk – resistant bacteria carried by animals transfer to vets, farmers and slaughtermen.
Hospital risk – high use of antimicrobials, selection for resistant hospital infections.
94
What promotes antimicrobial resistance?
Increased use promotes antimicrobial resistance. If antimicrobial is taken away often fairly rapid decrease in resistance in target organisms found.
95
Name 4 solutions of antimicrobial resistance.
New antimicrobials
Prudent use
Withdrawal periods
Licensed use
96
Describe prudent use of antimicrobials.
- Sparingly – only if needed
- Targeted – preferably narrow spectrum
- Correctly – at right dose and duration
- Preferably after firm diagnosis and resistance pattern assessment, which is not always possible.
97
Describe antimicrobial withdrawal periods.
- Every antimicrobial substance has prescribed withdrawal period: within withdrawal periods milk and eggs must not be used for human consumption, animals must not go for slaughter
- After withdrawal period antimicrobial removed from body tissues through metabolism or excretion
98
Describe licensed antimicrobial use.
- Antimicrobials only used if licensed for animal species and treatment indication
- Some antimicrobials only used as last resort – specifically if essential for human use
- Horses: scope of medicines narrower if horse ends up in consumption
99
What information can prescribers use?
- The name, address and telephone number of the person prescribing the product
- Qualifications
- The name and address of the owner or keeper
- Identity species
- The premises at which the animals are kept
- The date of the prescription
- The signature of the person prescribing the product
- The name and amount of the product prescribed
- The dosage and administration instructions
- Warnings
- The withdrawal period, if relevant
- If it is prescribed under the cascade, a statement to that effect
100
What is the prescribing cascade used for?
For food producing animals. If there is no medicine authorised in the UK for a condition affecting a food producing species, the veterinary surgeon is responsible for treating the animals and may us ethe cascade options.
101
What are the species specific withdrawal periods?
- 7 days for eggs and milk
- 28 days for meat from poultry and mammals
- 500 degree days for meat from fish
102
Describe how horses are an exception to the cascade?
Only substances listed can be administered to food producing animals. If it is not on this list, it cannot be given to a foo producing animal/species under any circumstances. Horses passport exemptions but no other species can be legally exempted from the food chain.
103
What records must vet keep?
- Name of the veterinary surgeon
- Name of the product and the batch number
- Date of administration
- Amount administered
- Identification of the animals treated
- Withdrawal period
104
What is responsible use of antimicrobials?
- Do not use inappropriately
- Right antimicrobial for the illness
- Right dose for the weight of the animal
- Complete the course
- Use antimicrobials prophylactically with caution
- Do not use modern antibiotics e.g. 3rd/4th generation Cephalosporins or Fluoroquinolones, as first line of treatment or where older antibiotics would work
- Use antimicrobials in accordance with the label
- Use an antimicrobial under the cascade as an exception
- Use as little as possible and as much as necessary
105
Define VMP.
- Any substance or combination of substances presented as having properties for treating or preventing disease in animals.
- Any substance or combination of substances that may be used in, or administered to, animals with a view either to restoring, correcting or modifying physiological functions by exerting a pharmacological, immunological or metabolic action, or by making a medical diagnosis.
