9.16.2022. study questions

Question 1

why is penicillin G not effective against most G- bacteria?

Answer 1

the outer membrane of G- covers the cell wall, and Penicillin G cannot penetrate the outer membrane to access the peptidoglycan

Question 2

why is penicillin G not effective against most Staphylococcus aureus strains?

Answer 2

Staph aureus strains produce penicillinase, which activates penicillin. so most staph aureus strains are resistant to natural forms of penicillin, like penicillin G.

Question 3

what is the key characteristic of each group in the “family of penicillins”?

Answer 3

all penicillin derivatives contain 6-aminopenicillanic acid (6-APA)

Question 4

how is the MIC of a strain determined?

Answer 4

tubes are examined for turbidity (cloudiness), which indicates growth. the lowest concentration of the medication that prevents growth of the microorganism is the MIC

Question 5

what does MIC test for?

Answer 5

lowest concentration of a specific antimicrobial medication that prevents the growth of a given microbial strain in vitro.

Question 6

what does the kirby-bauer test indicate?

Answer 6

the susceptibility of a bacterial strain to an antimicrobial drug

Question 7

does a large inhibition zone in the kirby-bauer assay with a drug indicated a low MIC or a high MIC with that drug?

Answer 7

large zone = low MIC, as drug concentration decreases as the zone spreads farther from the drug. a large zone means a lower concentration of the drug is required.

Question 8

what four general mechanisms allow a cell to resist the effects of an antimicrobial drug?

Answer 8

ie, Anie Du-Alt
1. increased elimination
2. antibiotic-inactivating enzyme
3. decreased uptake
4. alteration in target molecule

Question 9

in the case of certain antibiotics, a single point mutation allows a bacterial cell to become resistant to the drug. what can be done to prevent this type of resistance?

Answer 9

administering two or more antimicrobial medications at the same time to prevent growth of mutants that might be resistant to one of the antimicrobials

Question 10

in the case of many antibiotics, several different mutations must occur for a bacterial cell to become resistant to the drug. what can be done to prevent this type of resistance?

Answer 10

administer two drugs at once

Question 11

are antibiotics effective against viruses?
why or why not?

Answer 11

NO! viruses have no cell wall, ribosomes, or any other structure targeted by antibiotics.

Question 12

how do sub-therapeutic antibiotics given to animals lead to resistant infections in humans?

Answer 12

if you give animals a small amount of antibiotic medication over time, the bacteria living in those animals will become resistant to that drug. if we ingest the resistant bacteria via improperly cooked food and become ill, then we may not respond to antibiotic treatment

Question 13

what does M.I.C. stand for?

Answer 13

minimum inhibitory concentration

Question 14

how does the MIC test work?

Answer 14

growing the test strain in broth cultures containing different concentrations of the antimicrobial.

• serial dilutions are used to generate decreasing concentrations of the medication in tubes containing a suitable growth medium
• a standard inoculum of microbial cells is added to each tube
• tubes incubate for at least 16 hours and then examined for turbidity, which indicates growth
• the lowest concentration of the medication that prevents growth of the microorganism is the MIC

Question 15

when might I use an MIC test? (2)

Answer 15

1. if Kirby-Bauer test gives unclear results
2. if a company is developing a new antimicrobial medication

Question 16

what is the official name of the Kirby-Bauer test?

Answer 16

Kirby Bauer disc diffusion test of love

Question 17

what are the steps of a Kirby-Bauer test? (5)

Answer 17

SS, DD, GG, BB, ObZZ
spread the strain, distribute the discs, get the gradient, there’s a bacterial boom, then you obZerve the zone

1. standard inoculum of the strain is first uniformly spread on the surface of an agar place
2. 12 or so discs, each containing a known amount of a different antimicrobial, are placed on the surface of the medium
3. during incubation, the antimicrobials diffuse outward, forming a concentration gradient around each disc
4. meanwhile, the bacterial cells multiply, eventually forming a film of growth on the plate, except in regions around the discs where the bacteria were killed or their growth was inhibited
5. the clear area in which no visible growth occurs is called a zone of inhibition

Question 18

what is the zone of inhibition?

Answer 18

region around a disc where bacteria can’t grow because of the adverse effects of the compound in the disc

Question 19

what does the size of the zone of inhibition around an antimicrobial disc reflect?

Answer 19

the degree of susceptibility of the organism to medication

Question 20

in addition to the susceptibility of the organism to the medication, what influences the size of the zone of inhibition?

Answer 20

• characteristics of the chemical (molecular weight and stability)
• the amount in the disc

Question 21

based on the size of the zone and information in the chart, a bacterial strain can be described as… (3) to a particular antimicrobial

Answer 21

• susceptible
• intermediate
• resistant

Question 22

describe “increased elimination” mechanism of acquired resistance to antibiotics

Answer 22

antibiotic enters cell but efflux pump ejects it

Question 23

describe “antibiotic-inactivating enzyme” mechanism of acquired resistance to antibiotics

Answer 23

enzyme modifies antibiotic, inactivating it

Question 24

describe “alteration in target molecule” mechanism of acquired resistance to antibiotics

Answer 24

antibiotic cannot bind target

Question 25

describe “decreased uptake” mechanism of acquired resistance to antibiotics

Answer 25

porin proteins prevent antibiotic entry into the cell

Question 26

what is 6-APA?
aka what does it stand for and what is it and why does it matter?

Answer 26

6 aminopenicillanic acid
core portion of penicillin G.
common characteristic of each group in the family of penicillins