Lectures 1 & 2 - Clinical Bacteriology I & II Flashcards
(148 cards)
1
Q
What is the human microbiome?
A
Ecological community of commensal, symbiotic, and pathogenic bacteria that share our body space
2
Q
Which is larger: the human microbiome or the human genome?
A
Human microbiome (over 1M genes compared to 23K)
3
Q
Does the microbial community composition differ at different body locations?
A
YUP
4
Q
What are the 6 dominant bacterial phyla in each of the different body sites?
A
- Firmicutes
- Bacteroidetes
- Fusobacteria
- Actinobacteria
- Cyanobacteria
- Proteobacteria
5
Q
Do we all have the same core composition of our microbiome?
A
YUP
6
Q
What is dysbiosis?
A
Shifts in the microbiome that cause many infectious diseases (e.g. IBD, T2 DM, necrotizing enterocolitis)
7
Q
What are biofilms? What to note? Example?
A
Bacterial communities growing in an organized manner on surfaces
Note: cells growing in biofilms are different from those growing in fluid (planktonic growth) => biofilm bacteria grow slower, they may use different metabolic pathways, are more antibiotic resistant, and have greater opportunity for horizontal gene transfer
Example: with a UTI, the bacteria in the urine have a different phenotype from those attaching to the bladder epithelium
8
Q
Why do biofilms not have a lot of time to grow?
A
Because the barrier epithelia desquamate
9
Q
What are the 3 non-shedding surfaces of the human body?
A
- Teeth
- Bone
- Prosthesis such as dentures, joints, heart valves, etc.
10
Q
Describe the growth of a biofilm. 5 steps.
A
- Adhesion to the surface of the substratum by receptor-ligand interactions: random event influenced by surface free energy and proinquity (nearness) of bacterial cells that are in fluid and bounce by Brownian movement
- Colonization: cell division
- Accumulation: creating a linking film
- Climax community: this causes physiological changes to the environment due to consumption and production of molecules, which permits other bacteria to attach to pioneers = succession causing interbacterial aggregation + formation of fluid channels in between micro-colonies of microorganisms
- Dispersal: the climax community is a dynamic entity where cells enter or leave promoting diversification => pieces of the climax community break off when they cannot resist the shear force of the fluid phase => can reattach downstream to start a new biofilm thanks to the extracellular polysaccharide
11
Q
Is adhesion of bacterium to the surface of the substratum reversible?
A
YUP
12
Q
What are pioneer organisms?
A
Bacterial species that originally adhere to the surface of the substratum
13
Q
Other name for interbacterial aggregation in a biofilm?
A
Co-aggregation
14
Q
Are the pioneer organisms actually binding to the subtratum?
A
NOPE - they are binding to a conditioning film derived from the fluid phase (e.g. plasma, saliva, respiratory secretions) by selective absorption of proteins
15
Q
Can climax communities grow on shedding surfaces of the body? What to note?
A
NOPE - unless there is a wound
16
Q
What allows bacteria to adhere to each other in a climax community?
A
Extracellular polysaccharides
17
Q
What are the pioneer bacteria on teeth?
A
Alpha-hemolytic streptococci
18
Q
Can biofilms grow on both biotic and abiotic surfaces?
A
YUP
19
Q
3 types of abiotic surfaces that biofilms grow on?
A
- Medical devices: orthopedic devices, transcutaneous devices, catheters
- Hospital equipment: hemodialysis machines, mechanical ventilators, shunts, surfaces
- Others: contact lens cases
20
Q
3 examples of diseases characterized by the growth of biofilms?
A
- Osteomyelitis
- Cystic fibrosis
- Otitis media
21
Q
How do clinicians think about bacteria?
A
As individual infectious agents that need to be isolated, identified, and tested for antibiotic susceptibility
22
Q
Describe the diagnostic cycle of infectious diseases. 11 steps.
A
- Patient consults a physician because of signs or symptoms suggesting an infectious disease
- Physician examines patient and makes a tentative clinical diagnosis
- Cultures from one or more anatomic sites may be indicated, depending on the findings of medical history and physical examination
- An appropriate specimen for culture must be collected and a transport container(s) selected that will maintain the viability of any pathogenic organisms during transit
- Once the specimen is received in the laboratory, the information on the request form is entered into a computer file or log book
- The specimens are examined visually and, depending on the physician’s order and the nature of the specimen, wet mounts and smears may be prepared and stained for microscopic examination
- Observations may or may not be immediately reported to the physician depending on the definitiveness of the results and specimens that require definitive identification of potentially pathogenic microbes are processed further
- One or more culture media are selected, or if viral diseases are suspected, appropriate cell lines are chosen that will be inoculated with a portion of the specimen. All agar plates are streaked for colony isolation; then plates, broths, and cell cultures are placed in an incubator with appropriate temperature and environmental conditions to maximize the growth and replication of microbes
- After a specified incubation period, the cultures are examined both visually and microscopically. Often presumptive microbial identifications can be made and antibiotic sensitivity testing is conducted.
- A final report is issued if a definitive answer can be given; if not, the report should be delayed while subcultures and additional test procedures are performed to identify the organisms definitively
- Physician interprets reports and institutes appropriate therapy
23
Q
How should a specimen container be labeled? What should be sent along with it?
A
The specimen container must be properly labeled with the patient’s name, location, date and time of collection, and type of specimen
Should be accompanied by a physician’s orders to be transcribed to a laboratory request form or entered into a computer data file (or both), including essential clinical findings, a working diagnosis, and any information that may require laboratory personnel to apply other than routine procedures to recover uncommon or particularly fastidious microorganisms
24
Q
What should a physician do when sending a specimen to a lab if an infectious disease, caused by less commonly encountered or fastidious microorganisms, is suspected? Why? Example?
A
Physicians should either call the laboratory or indicate on the laboratory request slip
Reason: certain culture media required for the optimum recovery of certain fastidious or slow-growing microorganisms may not be available or used in many laboratories
For example: the recovery of bacterial species belonging to the genera Brucella, Pasteurella, Moraxella, Haemophilus, Neisseria, Leptospira, Vibrio, Campylobacter, and Legionella, among others, may require special culture media or alternative techniques
25
Why should the physician indicate a working diagnosis to the lab analyzing a specimen?
Because special culture media, adjusted incubation temperatures, or alternative analytical techniques may be necessary
26
Can all human bacteria pathogen be cultivated on artificial media? Examples?
NOPE
Examples: Treponema pallidum and Mycobacterium leprae
27
What 8 variables must be considered to successfully cultivate bacteria in the clinical laboratory?
1. Temperature
2. pH
3. Gaseous requirements
4. Minerals and trace elements
5. Vitamins
6. Nitrogen sources
7. Carbon sources
8. Energy generation
28
What are the 5 different types of bacterial species based on gaseous requirements? Describe each. Which is most common clinically?
1. Obligate aerobes: completely dependent on the presence of O2 and cannot grow without it
2. Microaerophiles: require O2 at about 0.2 atmospheres (4%) and are inhibited, but not killed by higher O2 levels
3. Capnophiles: grow best in elevated CO2 (5-10%)
4. ***Facultative anaerobes: grow in the presence and absence of O2, but usually prefer growth in O2 because respiration yields 38 moles ATP/mole glucose vs fermentation yields only 2-3 moles ATP
5. Obligate anaerobes: cannot grow in the presence of O2 for unknown reasons (note: some anaerobes are ‘aerotolerant’)
29
What is the normal air composition?
1. N2 = 78%
2. O2 = 21%
3. CO2 = 0.03%
30
What is the media of choice for collecting the clinical specimen from a normally sterile site? What about for contaminated sites?
1. Sterile sites: liquid media such as blood bottles
2. Contaminated sites with the resident microbiota (skin and barrier epithelia): need to be plated onto a solid (agar) surface to allow dilution of the specimen and separation of the various bacteria in the specimen
31
What is the end point of growing and isolating bacteria?
To obtain a pure culture of the causative bacterium
32
What body sites are normally sterile?
Blood, CSF, urine
33
Are most human infections caused by single organisms?
YUP
34
How is a blood culture performed? 4 steps.
1. A minimum of 10 ml of blood is taken and injected into two or more "blood bottles" with specific media for aerobic and anaerobic incubation
2. Most cultures are monitored for 5 days
3. If a vial is positive (presents with turbidity) a gram stain is performed and the attending physician is notified that the patient is bacteremic
4. An aliquot of the blood bottle is sub-cultured onto agar media to isolate the pathogen for identification and antibiotic susceptibility testing
35
How to reduce the probability of obtaining a false positive when a blood culture is performed?
Multiple sets of cultures reduces the probability of having a positive culture due to skin contaminants:
Set 1 = L. antecubital fossa at 0 min
Set 2 = R. antecubital fossa at 30 min
Set 3 = R or L anticubital fossa at 90 min
36
Which take longer to grow: aerobic or anaerobic bacteria?
Anaerobic
37
What is the bacterial growth curve?
- X-axis: time
- Y-axis: log of the number of bacteria over time
Done with "batch cultures"
38
What are the 4 phases of the bacterial growth curve?
1. LAG PHASE
2. EXPONENTIAL (LOG) PHASE
3. STATIONARY PHASE
4. DEATH PHASE
39
What is a "batch culture" of a bacteria?
Bacteria grown with a fixed volume of liquid nutrient medium
40
Describe the lag phase of the bacterial growth curve. 5 and overall
1. Increase in cell size but little or no cell division
2. Intense metabolic activity
3. Uptake of nutrients and macromolecular biosynthesis of DNA, protein, etc.
4. Sensitivity to physical and chemical agents such as antibiotics
5. Uniform staining with Gram’s stain
=> adaptation to the host
41
Describe the exponential phase of the bacterial growth curve. 8 and overall
1. Maximum growth rate as far as the environment allows
2. Minimum generation time
3. Balanced growth
4. Cellular reproduction most active
5. Most susceptible to uptake of foreign DNA
6. Most susceptible to antimicrobial agents
7. Uniform staining with Gram’s stain
8. Possible exotoxin production
=> signs and symptoms with tissue destruction
42
Describe the stationary phase of the bacterial growth curve. 5
1. Growth rate slows
2. Number of bacterial deaths equals number of new cells
3. Metabolic rate slows
4. Production of secondary metabolites, e.g., antibiotics, spores, inducible enzymes
5. Phagocytosis aided by antibodies
43
Describe the death phase of the bacterial growth curve. 2 and overall.
1. Number of deaths exceeds number of new cells formed
2. Culture may die out, or a small fraction of the population may survive for a long time
=> bacterial mopping up and clearance
44
Other name for the death phase of the bacterial growth curve?
Logarithmic decline phase
45
5 methods to identify bacteria?
1. Direct microscopic examination
2. Antigen detection = serology
3. Cell component detection = chemical/biochemical analysis: for example, ability to utilize sugars and nitrogen sources or the activities of enzymes
4. Molecular diagnosis: DNA probes and/or PCR
5. Culture
46
2 subtypes of microscopic examinations of bacteria?
1. Wet mounts
| 2. Stains: Gram’s, acid fast, auramine-rhodamine, silver, etc.
47
What does a bacterial culture try to look for?
1. Colonial characteristics
| 2. Physiological/biochemical properties
48
2 types of shapes of bacteria?
1. Sphere => coccus
| 2. Rod => bacillus
49
4 types of coccus bacteria?
1. Single
2. Pairs = diplococcus
3. Clusters
4. Chains
50
4 types of bacillus bacteria?
1. Thin
2. Slender
3. Curved
4. Corkscrew
51
What does a gram stain test?
Tests for the presence of 2 different types of cell wall:
1. Gram (+) cell wall
2. Gram (-) cell wall
52
Example of disease that can be diagnosed by Gram's stain? Explain.
Bacterial meningitis with CSF specimen
6 possible causes:
1. Streptococcus pneumoniae: gram (+) diplococcus
2. Streptococcus agalactiae (group B): gram (+) chain coccus
3. Listeria monocytogenes: gram (+) rod
4. Neisseria meningitidis: intracellular gram (-) diplococcus
5. Escherichia coli: gram (-) rod
6. Haemophilus influenzae: encapsulated gram (-) coccobacillus
53
How to conduct a Gram's stain?
1. Place a drop of specimen on slide and allow it to air-dry
2. Heat fix-it under a flame
3. Add crystal violet and let it sit for 30 sec
4. Wash it off with water
5. Add Lugol's iodine and let it sit for 30 sec
6. Wash it off with water
7. Lugol's iodine forms a complex with the crystal violet which lodges in the cell wall
8. Run alcohol along the surface of the slide to try to remove the complex from the cell wall
9a. If complex cannot be removed => cell is stained purple => gram (+) bacterium
9b. If complex is removed => gram (-) bacterium => safranin counter-stain is used
54
What is important about the bacteria Listeria monocytogenes?
It can cross the placenta
55
What is an acid-fast stain used for? What color does it stain?
To test for organisms that belong to the genus mycobacterium (e.g. tuberculosis) => carbol fuchsin stains mycobacterium as red beaded rods and the background stains blue with methylene blue
56
How can you tell the specimen for tuberculosis test is a deep sputum for the respiratory tree?
Inflammatory cells are present
57
3 types of agar-based media?
1. General purpose media
2. Differential and partly selective media
3. Selective media
58
Describe general purpose agar-based media. 2 subtypes?
Nutritionally rich media used in the primary recovery of human pathogens
1. Blood agar: contains 5% sheep blood => ‘indicator’ medium that reveals the production of hemolysins (cytotoxic exotoxins) by bacteria by the lysis of the red blood cells (RBCs) in the medium
2. Chocolate agar: more nutritious than blood agar because the RBCs are lysed (higher temp) and release cofactors such as NAD and hemin into the medium => used to recover fastidious human bacterial pathogens
59
Describe differential and partly selective media. 2 subtypes?
Designed to favor the growth of certain groups of bacteria while inhibiting others (usually gram (+) bacteria) and cause the pigmentation of certain bacterial colonies
1. Mannitol-salt agar
2. MacConkey agar
60
Describe selective media.
The only selective medium rountinely used in the clinical laboratory is Thayer-Martin agar which is used to isolate Neisseria gonorrhoeae and N. meningitidis when the clinical specimens are taken from the skin or mucosae
Consists of chocolate agar with vancomycin, colistin and nystatin => formulated to minimize the overgrowth of gonococci and meningococci by contaminants, to suppress the growth of saprophytic Neisseria species and to enhance the growth of pathogenic Neisseria
61
2 types of hemolysis performed by bacteria? 2 names for each. Describe each.
1. Beta hemolysis = complete hemolysis: hemolysins diffuse out and destroy RBCs so if you hold the plate up to a light you can see all the way through it
2. Alpha hemolysis = incomplete hemolysis: RBCs change color but are not lysed usually due to the production of hydrogen peroxide by the bacterium
62
What is an example of a fastidious human bacterial pathogen?
Haemophilus influenzae
63
What is an example of a fastidious human bacterial pathogen?
Haemophilus influenzae
64
What are differential partially selective media often used for?
Enteric infections
65
Nutritional medium of differential partially selective media? How does this work? Examples!!
Lactose:
1. Lactose-fermenters (e.g. E. Coli and Klebsiella) => colony becomes colored (pink/purple)
2. Non-lactose fermenters (e.g. Pseudomonas salmonella) => colorless colony where enteric bacteria grow
66
What are some colonial characteristics that can be used to identify the bacteria? What to note?
Different bacterial species produce different colony morphologies e.g., size, shape, color texture, etc. => sometimes the colony is sufficiently unique that it can serve to identify the bacterium
NOTE: this is the exception rather than the rule
67
What is important to note when testing antibiotics on colonies?
Colonies are clonal so antibiotic susceptibility testing should be done on several colony
68
Example of biochemical test to identify bacteria?
Phoenix system: 96 wells with different substrates to test the reaction with the bacteria
69
What are the 8 major differences between prokaryotes and eukaryotes?
1. Size: eukaryotes are > 5 micrometers/prokaryotes are between 0.5 and 3 micrometers
2. Nucleus: eukaryotes have a classic nuclear membrane/prokaryotes do not have one
3. Chromosomes: eukaryotes have a diploid genome with strands of DNA/prokaryotes have a haploid genome with a single circular DNA
4. Cytoplasmic structures: eukaryotes have mitochondria, Golgi bodies, ER, 80 S ribosomes (60S+40S), and a cytoplasmic membrane that contains sterols/prokaryotes only have 70S ribosomes (50S+30S) and have a cytoplasmic membrane that does not contain sterols
5. Cell wall: eukaryotes either do not have one or it is composed of chitin/prokaryotes have a cell wall with a complex structure contain proteins, lipids, and peptidoglycans
6. Reproduction: eukaryotes: sexual or asexual/prokaryotes: asexual (binary fission)
7. Movement: eukaryotes use a complex flagellum if present/prokaryotes use a simple flagellum if present
8. Respiration: eukaryotes do it via their mitochondria/prokaryotes do it via their cytoplasmic membrane
70
What only 2 prokaryotes lack a cell wall? Implication?
1. Mycoplasma
2. Ureaplasma
Implication: their cytoplasmic membrane contains sterols
71
Major 5 groups of eukaryotes?
1. Algae
2. Fungi
3. Protozoa
4. Plants
5. Animals
72
Major group of prokaryotes?
Bacteria
73
Since prokaryotes do not have many organelles, what replaces their functions?
The cytoplasmic membrane
74
What do most antibiotics target?
Some point in the assembly of the bacterial cell wall
75
What 3 bacterial components are important for adherence?
1. Pili
2. Fimbriae
3. Capsule
76
What 2 bacterial components are anti-complementary?
1. Capsule
| 2. Proteases
77
What 2 bacterial components are anti-phagocytic?
1. Capsule
| 2. Leukotoxins
78
Other name for leukotoxins?
Cytotoxins
79
What 5 bacterial components are important to subvert humoral immunity?
1. Fc receptors
2. Ig proteases
3. Endotoxins
4. LPS/LTA
5. Cell wall components
80
What bacterial components are important to subvert cellular immunity?
Superantigens
81
What bacterial components are important to cause cell and tissue damage?
Exotoxins
82
What do bacterial vaccine antigens comprise?
A lot of the bacterial components important in host-pathogen interaction like their capsule and exotoxins
83
How are bacteria plastic?
They sense their environment and they only express some specific structures when necessary
84
Other names for bacterial capsule?
Slime = glycocalyx
85
Where is the bacterial capsule with regards to the cell wall?
External to the cell wall
86
Is the bacterial capsule present in both gram (+) and (-) bacteria?
YUP
87
What is the bacterial capsule made of?
Usually carbohydrates, but can be proteins (in genus bacillus)
88
What is the bacterial capsule termed in gram (-) bacteria?
K antigen
89
What does it mean for the bacterial capsule to be antigenically diverse?
Bacteria can have different types of antigenic capsules
90
For what 3 bacteria are capsules the vaccine antigen?
1. Pneumococcus
2. Meningococcus
3. Haemophilus influenzae type b
91
Do bacterial flagella contribute to virulence?
YUP
92
How are bacterial flagella anchored?
Anchored in the cytoplasmic membrane
93
What are flagella composed of? What to note?
Flagellin helically arranged
NOTE: flagellin protein is a PAMP
94
What are flagella driven by? How does this work?
Proton-motive force
1. Counter-clockwise rotation bundles the flagella into a propeller
2. Clockwise rotation unbundles the flagella
95
What are the different flagella antigenic types based on?
Flagellin sub-unit
96
What is the bacterial flagellum termed in gram (-) bacteria?
H antigen
97
What are the principal bacterial organs of adhesion? How?
Fimbriae and pili
They serve as adhesins via lectin or protein-protein interactions
98
What are fimbriae and pili composed of? What to note?
Fimbrillin sub-units
NOTE: they are PAMPs
99
Are fimbriae and pili antigenically variable?
YUP
100
Which bacterial structural components undergo phase variation? What does this mean?
Fimbriae and pili
They are able to switch on (when the bacteria are trying to attach to the host surface) and off (once they get past the barrier epithelium)
101
What are the 5 different types of fimbriae/pili? What differentiates them?
GRAM (-) BACTERIA
1. Type I pili
2. Type IV pili
3. Curli pili
GRAM (+) BACTERIA
4. Fibrils
5. Pili
Mainly differentiated by their biogenesis aka how they are secreted
102
Can a particular bacterium express different types of pili/fimbriae?
YUP
103
Where is the adhesion site of the pilus/fimbra? How?
The tip recognizes carbs on the surface of cells
104
Describe the structure of the peptidoglycans in the bacterial cell walls.
1. Sugar backbone of repeating N-acetylglucosamine and N-acetylmuramic acid
2. Tetrapeptide bound to N-acetylmuramic acid: L-alanine + D-glutamic acid + diaminopimetic acid (gram +) or lysine (gram -)/another di-AA + D-alanine
3. Peptide cross-link between 2 tetrapeptides (di-AA to D-alanine) which varies between different types of bacteria and is not present in gram (-) bacteria
105
What portion of the bacterial peptidoglycan is an adjuvant used in humans? What is it exactly?
N-acetylmuramic acid-L-alanine-D-glutamic acid
It's a MAMP
106
Describe the cell wall of gram (+) bacteria.
Thick cell wall which is extensively cross-linked with the peptidoglycan content accounting for approx. 50% of dry weight
107
Example of gram (+) bacteria? Peptide cross-link?
Staphylococcus aureus
Peptide cross-link: penta-glycine peptide
108
What are the 2 types of gram (+) cell walls? How do they differ?
1. Classic peptidoglycan gram (+) bacteria cell wall
2. Mycobacterial cell wall: modified gram-positive type cell wall => in addition to peptidoglycan, the wall contains a large amount of glycolipids, especially hydrophobic mycolic acids linked to the peptidoglycan via arabinogalactan (D-arabinose and D-galactose) + the arabinogalactan/mycolic acid layer is overlaid with a layer of polypeptides and mycolic acids consisting of free lipids, glycolipids, and peptidoglycolipids (e.g. lipoarabinomannan and phosphatidyinositol mannosides (PIM))
109
How does the mycobacterium cell wall stain? Why?
Because of its unique cell wall, when it is stained by the acid-fast procedure, it will resist decolorization with acid-alcohol and stain red, the color of the initial stain, carbol fuchsin BECAUSE it is extremely hydrophobic and impermeable
With the exception of a very few other acid-fast bacteria such as Nocardia, all other bacteria will be decolorized and stain blue, the color of the methylene blue counterstain
110
Other than peptidoglycans, what are the other components of gram (+) cell walls? Are these immunogenic?
1. Teichoic acids covalently linked in the wall
2. Lipoteichoic acids terminating in glycolipids anchored in the cytoplasmic membrane
YUP, immunogenic
+ many other components dependent on the genus and species
111
What type of molecules are teichoic and lipoteichoic acids?
Glycerophophate polymers (lipopolysaccharides)
112
Special roles of TAs and LTAs?
Involved in adhesion and nutrition
113
Which is more complex: the cell wall of the gram (+) or gram (-) bacteria?
Gram (-) bacteria cell wall
114
Describe the cell wall of gram (-) bacteria.
The peptidoglycan is reduced to a single layer that is gelatinous rather than rigid as it is in the gram-positive wall and the peptidoglycan is sandwiched between the inner (cytoplasmic membrane) and an outer membrane (asymmetrical and composed of 40% LPS and 60% proteins) in a region called the periplasmic space
115
What is special about the LPS of the cell wall of the gram (-) bacteria?
Most powerful immureactive molecule (and MAMP) that activates polyclonal B cells (B-cell mitogen), the complement cascade and induces the release of cytokines from macrophages and other cells causing fever, shock and disseminated intravascular coagulation (DIC)
116
Describe the precise composition of the LPS of gram (-) bacteria cell wall.
1. Inner: lipid A
2. Middle: core polysaccharide (inner and outer)
3. Outer: O-polysaccharide
117
Other name for O-polysaccharide of the LPS of gram (-) bacteria cell wall? Why?
Somatic antigen
Highly antigenically variable
118
What is the role of the porins in the cell wall of gram (-) bacteria?
Proteins that form pores or channels through outer membrane for passage of hydrophilic molecules
119
What anchors the outer membrane to the peptidoglycan in the cell wall of gram (-) bacteria?
Lipoproteins
Purpose: to prevent it from floating away
120
Is the gram (+) or (-) cell wall a more effective barrier than the other? Why?
The gram-negative cell wall is a much more effective barrier than the gram-positive cell wall because it is amphiphilic and because the peptidoglycan is protected by the outer membrane so is far less susceptible to beta-lactam antibiotics
121
What is the outer membrane of E. coli composed of (gram (-) bacteria)? 4
1. Lipopolysaccharide (LPS): permeability barrier
2. Outer membrane proteins (OMP): Omp C and Omp F porins and Omp A, a transmembrane protein that stabilizes the outer membrane
3. Braun lipoprotein: anchors OM to peptidoglycan
4. Mg++ bridges: stabilizes LPS and is essential for its permeability characteristics
122
What does the periplasmic space of gram (-) cell walls contain? What is embedded in? Purpose?
Contains hydrolytic enzymes (some of which contribute to virulence), sugar transport system, nutrient-binding proteins => import/export space
Embedded in a polysaccharide gel
123
Describe the DNA in prokaryotes in detail. What is it called?
NUCLEOID = long, single molecule of double stranded, helical, supercoiled DNA the ends of which are covalently bonded together to form a circle
124
What does the presence of the nucleoid in the cytoplasm of bacteria allow?
Allows coupled transcription and translation
125
What are extrachromosomal DNA plasmids? What to note?
Independent, circular, double-stranded self-replicating DNA molecules that carry only a few genes, which are non essential but confer a selective advantage, e.g. encode antibiotic resistance, exotoxin production, unique substrate metabolism
NOTE: they are readily transferred within bacterial species, and genera
126
Describe the mechanism of binary fission (3 steps). What to note?
1. Cell elongates and DNA is replicated and segregates to opposite ends of the cell
2. The many types of proteins that comprise the cell division machinery assemble at the future division site (especially monomers of the protein FtsZ, which assemble into a ring-like structure at the center of a cell to recruit other cell division proteins, and define the division plane) => machinery positioned so that division splits the cytoplasm and does not damage DNA in the process
3. As division occurs, the cytoplasm is cleaved in two, and in many bacteria, new cell wall is synthesized
NOTE: the order and timing of these processes are tightly controlled
127
What can be said of the bacterial cytoskeleton proteins?
They are orthologs of the cytoskeleton proteins in eukaryotes
128
Role of actin-like MreB cytokeletal protein? In which bacteria is it found?
Actin-like MreB homologues exhibit helix-like localization patterns and are essential for cell width control
Most rod-shaped bacteria
129
Role of crescentin cytokeletal protein? In which bacteria is it found?
Intermediate filament-like crescentin is required for cell curvature and localizes at the inner curvature of cells
Found in C. Cresentus (vibrioid bacterium)
130
What do bacteria use inclusion granules for? What are they made of?
To store glycogen/starch and lipids when they are in an environment where nutrients are lacking
Made of polyphosphate metachromatic (volutin) that form branched rods (sometimes called Chinese letters)
131
What bacteria are inclusion granules characteristic of?
Corynebacterium diphtheriae
132
Which bacteria are able to form spores?
Clinically relevant gram (+) bacteria only
133
What are the 2 genera of spores to know?
1. Bacillus: aerobic gram (+) rod (Bacillus anthracis and cereus)
2. Clostridium: anaerobic gram (+) rod (perfringens, difficile, botulinum, tetani)
134
Where are the spores within bacteria?
Depends on the species: center, end of the cell, sub-terminal
135
When do gram (+) bacteria produce spores? Explain how this works.
Limitation in alanine AA in the environment
Bacterium undergoes binary fission and one of the daughter cells is enclosed in a complex structure in which necessary cellular machinery to allow the cell to become vegetative until it gets to a suitable environment to support its growth
136
Clinical relevance of bacterial spores?
When patients have been exposed to long-term antibiotics they can acquire these spores in the environment (inhaled or ingested) => vegetative cells that elaborate toxins
137
Plasmid host range?
Narrow to broad
138
Plasmid size range?
3-150 kb
139
Plasmid stability?
Depends on selective pressure or toxicity to the host cell
140
2 types of plasmids? Describe each.
1. Conjugative: can initiate cell conjugation = self-transmissible
2. Nonconjugative: cannot initiate cell conjugation without the help of conjugative
plasmids => either mobilizable or not
141
How many plasmids in a bacterial cell?
Low to high
142
2 important phenotypic functions of plasmids?
1. Antibiotic resistance
| 2. Resistance to heavy metals
143
How does a Mannitol-salt agar work?
Designed for the recovery of staphylococci from the skin
1. Selective agent: sodium chloride (7.5%) as staphylocooci can withstand high levels of salt whereas few other bacteria can't
2. Differentiating component: sugar alcohol mannitol as S. aureus ferments mannitol readily whereas other species of staphylococci do not
3. Indicator: pH indicator phenol red as S. aureus colonies turns phenol red to yellow so that colonies turn yellow and there is a yellow halo in the agar around each colony
144
How does the MacConkey agar work?
Selective and differential culture medium designed to selectively isolate Gram (-) and enteric bacilli and differentiate them based on lactose fermentation
145
Describe how cytoskeletal proteins work in C. crescentus.
At the onset of division in C. crescentus, MreB exhibits FtsZ-dependent relocalization from a helix-like to a ring-like pattern at the FtsZ ring location
146
What is the attachment site for conjugation with gram - bacteria?
Outer membrane of cell wall
147
Does the outer membrane of the gram - cell wall contain determinants of pathogenesis?
YUP
148
Does the mycobacterial cell wall have teichoic acid and lipoteichoic acid? What to note?
NOPE - lipoarabinogalactan takes the place of LTA and there doesn't appear to be a substitute for TA
