2.3.2 Bacterial Growth and Physiology

Question 1

Describe the different phases of the bacterial growth curve

Answer 1

1. Lag
2. Exponential
3. Stationary
4. Decline

Question 2

What is generation time?

Answer 2

Time it takes for culture to double in #

Question 3

Describe a biofilm and why infections that produce these are hard to treat

Answer 3

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

Question 4

Define obligate anaerobes, obligate aerobes, microaerophilic organisms, and facultative anaerobes

Answer 4

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)

Question 5

Explain why some bacteria die in the presence of oxygen whereas others do not.

Answer 5

Generally, obligate anaerobes tend to lack enzymes such as catalase and superoxidismutase leaving them vunerable to radical oxygen species

Question 6

Why is iron such an important nutrient for bacteria?

Answer 6

In an oxidizing environment, most nutrients are plentiful but free iron is oxidized to Fe(OH)₃, which is extremely insoluble

Question 7

How do bacteria obtain iron from their host?

Answer 7

The production of siderophores (molecules w/ high affinity for iron) to scavenge iron

Some bacteria acquire iron directly from cellular proteins (hemoglobin)

Question 8

Describe the semi-permeable nature of the cytoplasmic membrane

Answer 8

Utilizes mulitple transport mechanisms including diffusion, passive diffusion, and active transport (common)

Question 9

What is the difference b/t catabolism and anabolism?

Answer 9

Catabolism: energy-yielding metabolism

Anabolism: biosynthetic metabolism

Question 10

Differentiate between respiration and fermentation and how they produce energy

Answer 10

Fermentation: occurs in the absence of electron acceptor

-recycles NADH through reduction of pyruvate

Question 11

What is an antibiotic?

Answer 11

Bactericidal or bacteriostatic in nature

Question 12

What are 3 biochemical mechanisms of abx resistance?

Answer 12

1. Enzymatic inactivation or modification of antibiotic (beta lactamases)
2. Modification of target site
3. Altered permeability - change in porin, efflux pump

Question 13

What are 2 genetic mechanisms of abx resistance?

Answer 13

1. Chromosomal mutation
2. Genetic exchange - acquisition of a resistance gene (usually on a plasmid)

Question 14

What is a beta-lactam? What is its target in bacteria? Why is it bactericidal?

Answer 14

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

Question 15

Compare the outcome of the interaction of a beta-lactam with a penicillin-binding protein and a beta-lactamase.

Answer 15

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

Question 16

Define the mechanism of action of vancomycin and why it works on strains resistant to penicillin.

Answer 16

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

Question 17

What is the target of quinolones?

Answer 17

DNA synthesis, more specifically topoisomerases

Question 18

What is the target of rifampin?

Answer 18

RNA polyermase and its binding of promoters

Question 19

Name some drugs that inhibit/target protein synthesis

Answer 19

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

Question 20

Describe why colistin is only effective against Gram negative bacteria

Answer 20

Colistin binds to LPS and disrupts the membranes. It is only effective against gram negative bacteria because LPS is specific to gram negative bacteria.

Question 21

The principle of selective toxicity governs our use of abx in rx of bacterial infections.

Rampfampin is selectively-toxic to bacteria b/c:

Answer 21

C. Human RNA polymerase is less sensitive to rifampin

Question 22

Describe how bacteria utilize glucose. Describe the pathways that bacteria use to breakdown glucose.

Answer 22

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).

Question 23

Compare the import of nutrients by bacteria and the different sources of energy utilized.

Answer 23

Note:

• 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