AST

Question 1

what is the difference between a bactericidal and bacteriostatic?

Answer 1

bactericidal: kills bacteria
bacteriostatic: inhibits bacteria

Question 2

what is it called when an organism becomes resistant to several drugs at once when a single change occurs in the bacterial cell?

Answer 2

cross resistance

Question 3

what is constitutive resistance expression?

Answer 3

organism is constantly expressing the resistance mechanism

Question 4

what is inducible resistance expression?

Answer 4

resistance is expressed when exposed to the appropriate antimicrobial agent

Question 5

what is constitutive-inducible resistance expression?

Answer 5

organism is constantly expressing resistance at low level. and resistance at high level when exposed to appropriate antimicrobial agent

Question 6

what is homo and heterogenous resistance expression?

Answer 6

homo: entire bacterial population expresses resistance

hetero: some bacterial cells in a population express resistance, but others do not

Question 7

what are the four classes of beta-lactam antimicrobial agents?

Answer 7

penicillins, cephems, carbapenems, and monobactams

Question 8

what is the mechanism of beta-lactams? Why are they considered bactericidal?

Answer 8

they inhibit cell wall synthesis by binding to penicillin binding proteins

bactericidal due to simulating autolytic enzymes that lyse bacterial cells

Question 9

most __ produce penicillinase and are resistance to natural penicillins

Answer 9

Staph spp.

Question 10

extended-spectrum penicillins are developed to treat ____, and these include what three kinds of penicillins?

Answer 10

treat GNB

Aminopenicillins, carboxypenicillins, and ureidopenicillins

Question 11

what is one example for 1st and 2nd generation cephams?

Answer 11

1st gen: cefazolin
2nd gen: cephalosporins

Question 12

Aminoglycosides are inhibitors of ______ ______. What are two side affects of these kinds of antimicrobials? What bacteria are they used for?

Answer 12

inhibit protein synthesis

side affects: nephrotoxicity and ototoxicity

used for enterics and P. aeruginosa

Question 13

Vancomycin and Teicoplanin are both examples of _________. They interfere with the formation of ________ cross-links by binding to cell wall components, which means they are active against gram ____ organisms

Answer 13

glycopeptides

they interfere with formation of peptidoglycan cross-links

work against gram pos organisms

Question 14

what are VRE and VISA/VRSA?

Answer 14

VRE: vanco resistance enterococci (resistance genes VanA and VanB)

Vanco-intermediate-resistance Staph aureus

Question 15

Quinolones work by inhibiting ____ synthesis by binding to ___ _____. You do not give this drug to which population?

Answer 15

DNA

DNA gyrase

do not give to pregnant women and patients younger than 18 years old

Question 16

sulfanomides and trimethoprims (SXT) are used in combination against agents that do what?

Answer 16

bacteria that inhibit folic acid synthesis

Question 17

What spp. of bacteria have intrinsic resistance to SXT drugs and why?

Answer 17

Enterococci due to their ability to use exogenous folates, thymine, and thymidine

Question 18

Rifampin is used to inhibit _____ synthesis and how? Used prophylactically to treat people with _______. What color body fluids can be a side affect of taking this drug?

Answer 18

inhibits RNA synthesis by binding to RNA polymerase

treat people with meningitis

red-orange fluids

Question 19

metronidazole becomes a bactericidal when _________ (and enzyme in anaerobes) reduces the ____ group on a parent molecule that disrupts bacterial ___

Answer 19

when nitroreductase reduced the nitro group on a parent molecule. Disrupts bacterial DNA

Question 20

metronidazole is active against ____ and ________ parasites

Answer 20

anaerobes and protozoan parasites

(doesn’t work on aerobes due to these not having nitroreductase)

Question 21

Nitrofurantoin is used to treat ____

Answer 21

UTIs

Question 22

bacitracin acts on cytoplasmic membrane and is active against what kind of bacteria?

Answer 22

GPC

Question 23

polymyxins are used topically usually because they are ____- and ______. What bacteria are they active against?

Answer 23

neurotoxic and nephrotoxic

active against certain GNB

Question 24

Isoniazid (INH) treat what kind of organisms and how?

Answer 24

inhibit the synthesis of mycolic acid (treats mycoplasmas) and interact with catalase or peroxidase to form free radicals, which are toxic

Question 25

susceptibility testing standards are described by the ___?

Answer 25

CLSI (clinical and laboratory standards institute)

Question 26

what four things can affect test results when using a Mueller-Hinton agar/broth?

Answer 26

cation concentration pH thymidine blood

Question 27

what is the standard turbidity for McFarland standards?

Answer 27

"standardized suspension": 0.5 (has approx 1.5 x 10^8 CFU per mL)

Question 28

Broth dilution tests: macrodilution is performed in tubes that contain ___ of broth with diff concentrations of drug microdilution is performed in microtiter trays where each well contains ___ to __ of broth

Answer 28

macro: 1 mL micro: 0.05 to 0.1 mL

Question 29

size of zone (when it comes of disk diffusion tests) depends on what three things?

Answer 29

- ability of test drug to diffuse through the agar - susceptibility of the organism to the drug - agar depth

Question 30

positive beta-lactamase tests indicate that an isolate produces beta-lactamase, but it cannot do what?

Answer 30

it can't be used to predict the organism's susceptibility or resistance to a particular drug. But neg doesn't mean that it's susceptible either

Question 31

Beta-lactamase is produced constantly by what five organisms?

Answer 31

1. H. influenzae 2. N. gonorrhoeae 3. M. catarrhalis 4. enterococci 5. Bacteroides spp.

Question 32

Beta lactamase is inducible by what one spp.?

Answer 32

Staph spp.

Question 33

Nitrocefin is a _________ cephalosporin that is ___ when beta lactam ring is intact and turns ___ when the ring is hydrolyzed by beta lactamase

Answer 33

it's a chromogenic cephalosporin that is **yellow** when ring is intact and **red** when the ring is broken

Question 34

acidimetric beta lactamase testing uses ____ ___ to detect pH ____ when penicillin is hydrolyzed to penicilloic acid

Answer 34

uses phenol red yellow = positive red = negative

Question 35

iodometric beta lactamase testing uses _____-_____ complexes (blue) to detect penicilloic acid formation

Answer 35

starch-iodine (iodine reduced by penicilloic acid cannot form a color and the suspension becomes colorless, aka positive)

Question 36

beta lactamase tests should NOT be performed on what two groups of bacteria?

Answer 36

Enterobacterales and nonfermenters

Question 37

Oxacillin is used to screen for _____, and vancomycin is used to screen for ____

Answer 37

MRSA VRSA

Question 38

uncomplicated enterococci infections may be treated with a single agent: _________. What kind of agars can be used to screen for specific species of Enterococcus?

Answer 38

ampicillin Chromogenic agars

Question 39

Strep pneumo may now have ___ resistance

Answer 39

penicillin

Question 40

what is the minimum bactericidal concentration?

Answer 40

measures the ability of a normally bactericidal agent to kill a test organism - uses log-phase MIC growth method

Question 41

what are schlichter tests?

Answer 41

measures the antibacterial activity of a patient's serum against the patient's infecting organism

Question 42

what is a bacteriostatic/serum inhibitory test (SIT)?

Answer 42

is the highest serum dilution with no growth

Question 43

what is serum bactericidal titer?

Answer 43

the highest dilution that kills 99.9% of inoculum