Microbiology E3 Ch20

selective toxicity

selectively finding & destroying pathogens w/o damaging host

chemotherapy

use of chemicals to treat a disease

antibiotic

substance produced by a microbe that inhibits another microbe

antimicrobial drugs

synthetic substance that interfere with growth of microbes

narrow spectrum of microbial activity

drugs that affect a narrow range of microbial types

broad spectrum antibiotics

affect a broad range of gram(+) or gram(-) bacteria

when would you use broad vs narrow spectrum antibiotics

use broad when infection is unknown; use narrow when infection is identified

Bactericidal

kill microbes directly

Bacteriostatic

prevent microbes from growing (no killing)

Name the 5 major actions of antibacterial drugs

1. inhibit cell wall synthesis

2. inhibit protein synthesis

3. injure plasma membrane

4. inhibit nucleic acid synthesis

5. inhibit synthesis of essential metabolites

Antibiotics that inhibit cell wall synthesis (4)

1. penicillin

2. cephalosporins

3. bacitracin

4. vancomycin

how does penicillin inhibit cell wall synthesis

prevent peptidoglycan synthesis

Antibiotics that inhibit protein synthesis (4)

1. chloramphenicol

2. erythromycin

3. streptomycin

4. tetracyclines

how do antibiotics inhibit protein synthesis

target 70S ribosomes

Antibiotic that injure plasma membrane(1)

Polymyxin B

how do antibiotics injure plasma membrane (2)

1. change membrane permeability

2. antifungal drugs combine with membrane sterols

Antibiotics that inhibit nucleic acid synthesis (2)

1. Quinolones

2, rifampin

how do antibiotics inhibit nucleic acid synthesis

interfere with DNA replication & transcription

Antibiotics that inhibit synthesis of essential metabolites (2)

1. Sulfanilamide

2. trimethoprim

how do antibiotics inhibit synthesis of essential metabolites (2)

1. compete with normal substrates for an enzyme

2. sulfanilmide competes with para-aminobenzoic acid (PABA) -> stops synthesis of folic acid

Penicillin essential part

b-lactam ring (no ring = no penicillin)

Penicillin G vs Penicillin V

G - injected, higher blood retention

V - taken orally, lower blood retension

What inactivates penicillin (developed by bacteria)

Penicillinase

What are actions that can extend the life of antibiotics (4)

1. penicillinase-resistant penicillins

2. extended-spectrum penicillins

3. penicillins plus b-lactamase inhibitors

4. cephalosporins

antibiotics with penicillinase-resistant penicillins (2)

methicillin

oxacillin

what does extended-spectrum penicillins imply

effectiveness against gram (-) and gram (+)

antibiotics with an extended-spectrum penicillins (2)

ampicillin

amoxicillin

(both are types of aminopenicillins)

what causes a b-lactamase inhibitor

clavulanic acid; a noncompetitive inhibitor of penicillinase

cephalosporins compared to penicillin

work similar to penicillin, but with a different b-lactamase ring (grouped by generation of development

Name the 3 ways to test for microbial susceptibility to chemotherapeutic agents

disk diffusion method

e test

broth dilution test

explain the disk diffusion method

- antibiotic on paper disk placed on lawn of bacteria

- clear spaces around the disk form if the antibiotic is effective against the bacteria

explain the e-test

- take a strip of antibiotic of differing gradients and leave in agar plate

- test where bacteria stops growing -> lowest gradient = the MIC

explain broth dilution test

- wells with dif concentrations of antibiotics (obtained by dilution series)

- grow bacteria on wells -> cloudiness forms for growth (no cloudiness means no growth)

- lowest concentration well with no growth is MIC

- concentration well plated onto agar with no growth is MBC

- if plated and bacteria grows, bacteria is inhibited, not killed

3 types of resistances to antibiotics

persister cells

superbugs

enterobacteriaceae (resistance to nearly all antibodies)

persister cells

microbes with genetic characteristics allowing for their survival when exposed to an antibiotic

(dormant when exposed, normal when free)

superbugs

bacteria that are resistant to large numbers of antibiotics (trait spread horizontally via conjugation/transduction)

mechanisms of resistance to antibiotics (5)

enzymatic destruction/inactivation of the drug

prevention of penetration to target site within microbe (mutate membrane)

alteration of drug's target site (mutate ribosomal protein)

rapid efflux of drug

variations of mechanisms of resistance

describe development of antibiotic-resistant mutant during antibiotic therapy

1. sensitive cells killed with antibiotic

2. cell population dips; slightly resistant cells die via further exposure

3. cells that are resistant to antibiotic spread the trait

4. trait is passed on and cell population increases

6 possible antibiotic misuses

1. outdated/weakened antibiotics

2. antibiotics for common cold & other inappropriate conditions

3. antibiotics in animal feed

4. someone else's leftover prescription

5. wrong combination of antibiotics

6. failing to complete the prescribed regimen

4 antibiotic safety notices

1. therapeutic index (risk vs benefit)

2. reactions of antibiotics with other drugs

3. damage to organs

4. risk to the fetus

synergism

effect of 2 drugs together > effect of either alone

antagonism

effect of 2 drugs together < effect of either alone

8 possible futures for antibiotics

1. target virulence factors

2. sequester iron, which feeds pathogens

3. seeks drugs that combat dormant persister cells

4. more drugs that target gram (-) bacteria

5. ways to test the antimicrobial safety of nonculturable bacteria

6. antimicrobial peptide production

7. bacteriocins

8. phage therapy

phage therapy

using bacteriophage to treat infections

bacteriocins

antimicrobial peptides prod. by bacteria

where do antimicrobial peptides come from

various organisms