Microbiology Ch 5

Front 1

This substance, a component of folic acid, antagonizes the action of sulfonamides.

Back 1

p-aminobenzoic acid (PABA)

Front 2

The addition of what antibiotic to dihydropteroic acid inhibits the synthesis of folic acid?

Back 2

sulfanilamide

Front 3

When substance A is added, proportionally more of substance B is required to counteract its action. This is an example of what?

Back 3

competitive inhibition

Front 4

Why are body cells unaffected by sulfonamides?

Back 4

Because they require preformed folic acid.

Front 5

Sulfonamides inhibit the SYNTHESIS of folic acid, but not its UTILIZATION. So why aren't bacteria able to use other sources of preformed folic acid?

Back 5

Many bacteria that make folic acid lack a system for the uptake of preformed folic acid and cannot benefit from its presence in the environment.

Front 6

When sulfanilamide is added, why must bacteria progress through 2-4 generations before growth is inhibited?

Back 6

Each bacterium contains enough preformed folic acid to meet the demands of up to 16 daughter cells.

Front 7

Name a few important examples when bactericidal agents are preferred to bacteriostatic ones.

Back 7

bacterial endocarditis, bacterial meningitis and infections in patients with low numbers of circulating neutrophils

Front 8

Give an example when a bacteriostatic drug might be preferable to a bactericidal one.

Back 8

Infection with clostridium perfringes (agent of gas gangrene) or other toxin producing bacteria

Front 9

These antibiotics are taken up poorly by bacteria under anaerobic conditions and are thus ineffective against anaerobes.

Back 9

aminoglycosides

Front 10

This drug is concentrated in the urine and is effective in many cases of uncomplicated urinary tract infections.

Back 10

nitrofurantoin

Front 11

This drug blocks the function rather than the synthesis of folic acid.

Back 11

trimethoprim

Front 12

What is the mechanism of action for trimethoprim?

Back 12

It inhibits the enzyme dihydrofolate reductase, which catalyzes the reduction of dihydrofolate to tetrahydrofolate. The drug can be used against bacteria and protozoa at concentrations that do not harm humans.

Front 13

Three steps of action for antimicrobial drugs:

Back 13

1. associate with the bacteria and penetrate their evelope
2. be transported to an intracellular site of action
3. must bind to their specific biochemical target

Front 14

List five clinically relevant mechanisms of resistance:

Back 14

1. synthesis of enzymes that break down the drug molecule
2. chemical modification of the drug that interferes with its function
3. prevention of access to the target site by inhibiting uptake
4. prevention of access to the target site by increasing export of the drug from the microbial cell
5. modification of the target site

Front 15

what is the main difference between 1st and 2nd or 3rd generation cephalosporins

Back 15

the addition of new side chains to extend the spectrum of activity to organisms that were resistant and to increase penetration into the CNS

Front 16

List the 4 steps of bactericidal action of the B-lactams:

Back 16

1. association with the bacteria
2. penetration through the outer membrane and the periplasmic space (in gram neg)
3. interaction with penicillin-binding proteins on the cytoplasmic membrane
4. activation of an autolysin that degrades the cell wall murein

Front 17

Two major categories of B-lactamases:

Back 17

penicillinases and the cephalosporinases

Front 18

Where are the B-lactamases produced in gram (+) bacteria?

Back 18

extracellularly

Front 19

Where are the B-lactamases found in gram (-) bacteria?

Back 19

in the periplasmic space or bound to the inner membrane

Front 20

In gram (-) bacteria, B-lactams must be able to pass through outer membrane porins to make contact with what?

Back 20

penicillin-binding proteins (PBPs)

Front 21

Altering the PBPs so they no longer bind to B-lactams has been an important resistance mechanism for what two bacteria?

Back 21

PCN resistant streptococcus pneumoniae and methycillin resistant staphylococcus aureus

Front 22

This drug inhibits peptidoglycan chain elongation by binding to the D-ala-D-ala terminal peptides on the precursor

Back 22

vancomycin

Front 23

Mechanism of vancomycin resistance

Back 23

the production of precursors with D-lactate in the position of the terminal D-ala, thereby blocking the binding of vancomycin

Front 24

These antibiotics act by inhibiting the action of bacterial topoisomerases, including DNA gyrase (in gram pos) and topoisomerase IV (in gram neg)

Back 24

quinolones

Front 25

Three steps in the mechanism of action of aminoglycosides (an antiribosomal antibiotic)

Back 25

1. penetration of the outer membrane of gram (-)
2. association with a two-stage active transport system in the cell membrane (irreversible)
3. binding to the 30S ribosome subunit to inhibit protein synthesis, primarily at or near the initiation step, and to increase "miscoding" by the ribosomes and the production of "nonsense proteins."

Front 26

Most common mechanism in clinically important resistance of aminoglycosides:

Back 26

modifying enzymes that modify these antibiotics by the addition of acetyl, adenyl, or phosphoryl groups

Front 27

erythromycin, clindamycin, azithromycin and clarithromycin are examples of what kind of antibiotics?

Back 27

macrolide antibiotics

Front 28

elimination of antibiotics from bacterial cells is an example of what type of resistance?

Back 28

efflux pumps

Front 29

Linezolid, and entirely synthetic antibiotic is an example of what class of drugs?

Back 29

oxazolidinones

Front 30

These drugs bind more avidly to ergosterol in the membranes of fungi than to cholesterol in the membranes of higher eukaryotes.

Back 30

polyenes

Front 31

This group of anti-fungal drugs targets cytochrome P450 demethylase, which is involved in sterol synthesis.

Back 31

imidazoles

Front 32

This group of anti-fungals inhibits B-glucan, a component of the fungal cell wall.

Back 32

echinocandins

Front 33

what is transpeptidase?

Back 33

You might know it as penicillin binding protein (PBP). It is the enzyme that catalyzes the formation of the peptidoglycan linkages in the bacterial cell wall.