Bacterial Structure, Function and Growth II

Question 1

Classification due to nutritional requirements: Heterotrophic

Answer 1

Bacteria that require an organic carbon source (most bacterial pathogens)

Question 2

Classification due to nutritional requirements: autotrophic

Answer 2

bacteria that obtain their carbon exclusively from CO2

Question 3

Classification due to nutritional requirements: fastidious

Answer 3

Many bacterial pathogens that are deficient in one or more biosynthetic pathways require, in addition to sources of carbon and energy, a number of essential growth factors such as amino acids, vitamins, purines, pyrimidines and inorganic ions. They are typically grown in rich, complex growth media. Some bacterial pathogens are obligate intracellular bacteria that can grow within eukaryotic cells but cannot be cultivated on artificial media

Question 4

Growth response of bacteria: aerobe (aerobic vs. anaerobic response and example)

Answer 4

aerobic: +
anaerobic: -
requires ox, cannot ferment
ex. Mycobacterium tuberculosis

Question 5

Growth response of bacteria: anaerobe (aerobic vs. anaerobic response and example)

Answer 5

aerobic: -
anaerobic: +
killed by ox, fermentative metabolism
ex. Clostridium sp, Bacteroides sp.

Question 6

Growth response of bacteria: indifferent (aerobic vs. anaerobic response and example)

Answer 6

aerobic: +
anaerobic: +
ferments in presence or absence of O2
ex. Strep pyogenes

Question 7

Growth response of bacteria: facultative (aerobic vs. anaerobic response and example)

Answer 7

aerobic: +
anaerobic: +
respires with O2, ferments in absence of O2
ex. E. coli, S. aureus

Question 8

Growth response of bacteria: microaerophilic (aerobic vs. anaerobic response and example)

Answer 8

aerobic: (+)
anaerobic: +
grows best at low [O2], can grow without O2
ex. Campylobacteri jejuni

Question 9

Respiration:

Answer 9

generate ATP through electron transport and use molecular oxygen as the final electron acceptor. In anaerobic respiration, certain bacteria may use inorganic substrates such as nitrate or nitrite as terminal electron acceptors instead of O2

Question 10

Fermentation:

Answer 10

organic compounds serve as both electron donors and electron acceptors, and no net oxidation of substrates occurs. Both anaerobic and facultative or indifferent bacteria grown under anaerobic conditions obtain energy by fermenting organic substrates. Indifferent organisms (aerotolerant anaerobes, incapable of respiration), obtain energy by fermentation under either anaerobic or aerobic conditions.

Question 11

Metabolic “energy currency”:

Answer 11

two forms of “energy currency” in bacteria and higher cells: ATP and electrochemical gradients (the proton motive force). ATP drives many biosynthetic reactions, and electrochemical gradients drive other functions like flagellar rotation and certain substrate transport systems. These two types of potential energy are interconvertible by the membrane ATPase. Bacteria also require reducing power in the form of NADH and NADPH to drive various metabolic interconversions. Heterotrophic bacteria obtain both energy and reducing power by subjecting nutrients to fermentation or respiration

Question 12

Explain why unique bacterial components are important as potential targets for antimicrobial therapy

Answer 12

Some components of bacteria are not present in eukaryotes or are sufficiently different from their counterparts in eukaryotes be effective as targets for antimicrobial agents. Antimicrobials work on the principle of selective toxicity, namely the selective inhibition of microbial growth at drug concentrations tolerated by the host.

Question 13

Identify the principal targets for the major groups of antibiotics used in human medicine

Answer 13

• Cell wall-active antimicrobials
• Outer and cytoplasmic membrane-active antimicrobials
• Inhibitors of protein synthesis at the ribosomal level
• Inhibitors of nucleic acid synthesis
• Metabolic inhibitory antimicrobials

Question 14

Cell wall-active antimicrobials

Answer 14

Selective toxicity is due to the lack of peptidoglycan in mammalian cells.

• ex.
• -beta-lactams (penicillins, cephalosporins, etc.)
• -Vancomycin
• -Cycloserine

Question 15

Outer and cytoplasmic membrane-active antimicrobials

Answer 15

Polymyxins are cationic surfactants that disrupt bacterial outer and cytoplasmic membranes. They are less active on mammalian cell membranes

Question 16

Inhibitors of protein synthesis at the ribosomal level

Answer 16

Selective toxicity is due to differences between bacterial and mammalian ribosomes.

• ex.
• -Aminoglycosides (including streptomycin, kanamycin, gentamicin, neomycin, tobramycin, amikacin, etc)
• -Tetracyclines
• -Chloramphenicol
• -Macrolides (such as erythromycin) and lincomycins (such as lincomycin and clindamycin)

Question 17

Inhibitors of nucleic acid synthesis

Answer 17

ex.
- Quinolones
- Rifampicin

Question 18

Metabolic inhibitory antimicrobials

Answer 18

ex.
- Sulfonamides
- Trimethoprim
- Isoniazid
- Metronidazole