Exam 3- Antimicrobials

Question 1

For an antimicrobial drug to have selective toxicity it needs to…

Answer 1

kill microbial cells but not host cells

Question 2

What is a broad spectrum for antimicrobials?

Answer 2

effective against wide range of species, including both gram negative & positive species

Question 3

What is a narrow spectrum for antimicrobials?

Answer 3

only active against select species

Question 4

What is used to determine effectiveness of chemical agents against a particular microbe?

Answer 4

a disk-diffusion assay

Question 5

What is minimal inhibitory concentration?

Answer 5

MIC, lowest concentration of the drug that inhibits growth of the microbe

Question 6

What is used to determine the MIC of a drug?

Answer 6

a broth dilution test

Question 7

What is a therapeutic dose?

Answer 7

minimum dose per kg of body weight that inhibits growth of the pathogen

Question 8

What is a toxic dose?

Answer 8

maximum dose tolerated by the patient

Question 9

What is the chemotherapeutic index?

Answer 9

ration of the toxic dose to therapeutic dose

Question 10

When does synergism occur?

Answer 10

when the effect of two drugs together is greater than the effect of either alone

Question 11

When does antagonism occur?

Answer 11

when the effect of two drugs together is less than the effect of either alone

Question 12

Why do antibiotics exhibit selective toxicity?

Answer 12

because they disturb enzymes or structures unique to the target cell

Question 13

What is penicillinase (beta-lactamase)?

Answer 13

a beta-lactamase enzyme effective against penicillin

Question 14

What is bacitracin?

Answer 14

large polypeptide produced by Bacillus subtilis & Bacillus licheniformis

Question 15

What does bacitracin do?

Answer 15

inhibits cell wall synthesis by binding to the bactoprenol lipid carrier molecule that exports peptidoglycan disaccharide units across cell membrane

Question 16

What is vancomycin?

Answer 16

very large, complex glycopeptide produced by Amycolatopsis orientalis

Question 17

What does vancomycin do?

Answer 17

binds peptide end of newly exported NAM-NAG disaccharide & blocks addition to preexisting peptidoglycan

Question 18

What is mycobacterium?

Answer 18

cell wall contains mycolic acids & arabinogalactans

Question 19

What does isoniazid do?

Answer 19

INH, inhibits mycolic acid synthesis

Question 20

What does ethambutol do?

Answer 20

disrupts arabinogalactan synthesis

Question 21

What is polymyxin?

Answer 21

positively charged polypeptide ring from Bacillus polymyxa that binds to the outer & plasma membranes of bacteria, both of which are negatively charged

Question 22

What is inhibit replication?

Answer 22

bacterial replication uses enzymes that closely resemble human enzymes

Question 23

What are quinolones?

Answer 23

drugs that target topoisomerases like DNA gyrase, which introduces negative supercoils in DNA ahead of replication forks

Question 24

What are rifamycin?

Answer 24

class of drugs that includes rifampin that selectively binds to the bacterial RNA polymerase

Question 25

Why does erythromycin have a spectrum of activity limited mostly to gram-positive bacteria?

Answer 25

erythromycin is blocked by the gram negative cell wall. gram positive bacteria accumulate 100-fold more erythromycin than gram negative bacteria

Question 26

What do sulfonamides do?

Answer 26

inhibit folic acid synthesis

Question 27

What is folic acid?

Answer 27

an important cofactor in the synthesis of nucleic acid precursors

Question 28

What are selectively toxic targets for anti-fungal drugs?

Answer 28

ergosterol & beta-glucan

Question 29

What are the 4 antifungal drugs licensed for use in humans?

Answer 29

1. polyenes 2. flucytosine 3. echinocandins 4. azoles

Question 30

What do polyenes do?

Answer 30

disrupt cell membranes by binding ergosterol

Question 31

What does flucytosine do?

Answer 31

fluorouracil disrupts RNA synthesis; derivatives of FU disrupt DNA synthesis

Question 32

What do echinocandins do?

Answer 32

disrupt cell wall synthesis through inhibition of glucan synthase

Question 33

What do azoles do?

Answer 33

block ergosterol biosynthesis through inhibition of lanosterol demethylase

Question 34

What are antiviral agents hard to discover?

Answer 34

there are very few drugs targets unique to viruses

Question 35

What is acyclovir?

Answer 35

guanosine analog that lacks a 3' OH

Question 36

What is only found in viruses?

Answer 36

RNA-directed RNA polymerase

Question 37

What is Ribavirin?

Answer 37

ribonucleoside analog that resembles guanosine or adenosine; when incorporated into RNA, can pair with either uracil or cytosine

Question 38

What is ribavirin used to treat?

Answer 38

Hep C virus

Question 39

Explain the influenza virus.

Answer 39

an enveloped virus with glycoprotein spikes

Question 40

What does hemagglutinin do?

Answer 40

binds to the host membrane sialic acid receptors for entry by endocytosis

Question 41

What does neuraminidase do?

Answer 41

cleaves sialic acid to allow virus particles to escape from infected cells

Question 42

What do Zanamivir & oseltamivir (tamiflu) inhibit?

Answer 42

neuraminidase, prevents release of mature virus

Question 43

What does penicillin interfere with?

Answer 43

peptidoglycan synthesis

Question 44

Selective toxicity of penicillin.

Answer 44

because human cells do not have cell walls & do not synthesize peptidoglycan

Question 45

What are the mechanisms of antibiotic resistance?

Answer 45

modify the target, destroy the antibiotic, add modifying groups, pump the antibiotic out

Question 46

How do bacteria acquire antibiotic resistance?

Answer 46

can arise spontaneously through mutation or gene duplication followed by random mutations that repurpose the duplicated gene or genes

Question 47

What is horizontal transfer?

Answer 47

once resistance mechanism develops, resistance can spread from cell to cell & from species to species

Question 48

How many people get sick with antibiotic-resistant infections per year?

Answer 48

2.8 million

Question 49

How many people die from antibiotic-resistant infections per year?

Answer 49

35,000

Question 50

What can broad-spectrum antimicrobial use lead to?

Answer 50

development of a superinfection

Question 51

Misuse of antibiotics include..

Answer 51

not completing a prescribed course of antibiotics, using them for the common cold & other inappropriate conditions, using antibiotics in animal feed