Describe the different phases of the bacterial growth curve
What is generation time?
Time it takes for culture to double in #
Describe a biofilm and why infections that produce these are hard to treat
Biofilm: bacteria sticking to each other and a surface; bacteria produce a matrix to hold them together (exopolysaccharides, DNA, protein) - i.e. plaque
Hard to rx: phenotypic change due to change in gene expression, resistance to abx and host defenses
Define obligate anaerobes, obligate aerobes, microaerophilic organisms, and facultative anaerobes
obligate anaerobes: sensitive to oxygen (Clostridia)
obligate aerobes: require oxygen to grow, 20% (Myco tb)
microaerophilic organisms: require low oxygen, 5-10% (N. gonorrheae and Campylobacter jejuni)
facultative anaerobes: use oxygen if available (E. coli, Staphylococci)
Explain why some bacteria die in the presence of oxygen whereas others do not.
Generally, obligate anaerobes tend to lack enzymes such as catalase and superoxidismutase leaving them vunerable to radical oxygen species
Why is iron such an important nutrient for bacteria?
In an oxidizing environment, most nutrients are plentiful but free iron is oxidized to Fe(OH)3, which is extremely insoluble
How do bacteria obtain iron from their host?
The production of siderophores (molecules w/ high affinity for iron) to scavenge iron
Some bacteria acquire iron directly from cellular proteins (hemoglobin)
Describe the semi-permeable nature of the cytoplasmic membrane
Utilizes mulitple transport mechanisms including diffusion, passive diffusion, and active transport (common)
What is the difference b/t catabolism and anabolism?
Catabolism: energy-yielding metabolism
Anabolism: biosynthetic metabolism
Differentiate between respiration and fermentation and how they produce energy
Fermentation: occurs in the absence of electron acceptor
-recycles NADH through reduction of pyruvate
What is an antibiotic?
Bactericidal or bacteriostatic in nature
What are 3 biochemical mechanisms of abx resistance?
- Enzymatic inactivation or modification of antibiotic (beta lactamases)
- Modification of target site
- Altered permeability - change in porin, efflux pump
What are 2 genetic mechanisms of abx resistance?
- Chromosomal mutation
- Genetic exchange - acquisition of a resistance gene (usually on a plasmid)
What is a beta-lactam? What is its target in bacteria? Why is it bactericidal?
A molecule with a four member ring that mimics the D-ala-D-ala.
Target: Penicillin binding proteins (PBPs)
Bactericidal: bactericidal because the binding beta-lactam binding of PBPs blocks the transpeptidation process resulting in the impaired peptidoglycan cell wall synthesis
Compare the outcome of the interaction of a beta-lactam with a penicillin-binding protein and a beta-lactamase.
When a beta-lactam is introduced to a bacteria that produces beta-lactamase, the beta-lactamase binds the beta-lactam creating an unstable intermediate that ultimately results in dispruption/breaking of the beta-lactam ring. The broken beta-lactam ring is unable to interact with PBPs
Define the mechanism of action of vancomycin and why it works on strains resistant to penicillin.
Vancomycin binds directly to the D-ala D-ala region of the cell wall.
It works on strains resistant to penicillin because it doesn't have a beta lactam ring, which is the vulnerable motif of penicillin to beta-lactamases
What is the target of quinolones?
DNA synthesis, more specifically topoisomerases
What is the target of rifampin?
RNA polyermase and its binding of promoters
Name some drugs that inhibit/target protein synthesis
Tetracyclines, aminoglycosides*, macrolides, chloramphenicol, lincosamides, oxazolidinones
*Most of these tend to be bacteriostatic -- Aminoglycosides are an exception cause errors in protein synthesis leading to the build up of protein aggregates, which seems to be bactericidal
Describe why colistin is only effective against Gram negative bacteria
Colistin binds to LPS and disrupts the membranes. It is only effective against gram negative bacteria because LPS is specific to gram negative bacteria.
The principle of selective toxicity governs our use of abx in rx of bacterial infections.
Rampfampin is selectively-toxic to bacteria b/c:
C. Human RNA polymerase is less sensitive to rifampin
Describe how bacteria utilize glucose. Describe the pathways that bacteria use to breakdown glucose.
Bacteria use three pathways to utilize glucose. First they use glycolosis to break down glucose into pyruvate. From there, bacteria either use fermentation or respiration depending on the presence of an electron acceptor (O2).
Compare the import of nutrients by bacteria and the different sources of energy utilized.
- The outer membrane contains porins - allowing passage of small, hydrophilic molecules
- The cytoplasmic membrane contrains specific transporters that are coupled with different energy sources to drive the import of key nutrients