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Microbiology > AST > Flashcards

AST Flashcards

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Biology 101 flashcards
1
Q

what is the difference between a bactericidal and bacteriostatic?

A

bactericidal: kills bacteria
bacteriostatic: inhibits bacteria

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2
Q

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

A

cross resistance

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3
Q

what is constitutive resistance expression?

A

organism is constantly expressing the resistance mechanism

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4
Q

what is inducible resistance expression?

A

resistance is expressed when exposed to the appropriate antimicrobial agent

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5
Q

what is constitutive-inducible resistance expression?

A

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

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6
Q

what is homo and heterogenous resistance expression?

A

homo: entire bacterial population expresses resistance

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

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7
Q

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

A

penicillins, cephems, carbapenems, and monobactams

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8
Q

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

A

they inhibit cell wall synthesis by binding to penicillin binding proteins

bactericidal due to simulating autolytic enzymes that lyse bacterial cells

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9
Q

most __ produce penicillinase and are resistance to natural penicillins

A

Staph spp.

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10
Q

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

A

treat GNB

Aminopenicillins, carboxypenicillins, and ureidopenicillins

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11
Q

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

A

1st gen: cefazolin
2nd gen: cephalosporins

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12
Q

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

A

inhibit protein synthesis

side affects: nephrotoxicity and ototoxicity

used for enterics and P. aeruginosa

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13
Q

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

A

glycopeptides

they interfere with formation of peptidoglycan cross-links

work against gram pos organisms

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14
Q

what are VRE and VISA/VRSA?

A

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

Vanco-intermediate-resistance Staph aureus

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15
Q

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

A

DNA

DNA gyrase

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

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16
Q

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

A

bacteria that inhibit folic acid synthesis

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17
Q

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

A

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

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18
Q

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?

A

inhibits RNA synthesis by binding to RNA polymerase

treat people with meningitis

red-orange fluids

19
Q

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

A

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

20
Q

metronidazole is active against ____ and ________ parasites

A

anaerobes and protozoan parasites

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

21
Q

Nitrofurantoin is used to treat ____

A

UTIs

22
Q

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

A

GPC

23
Q

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

A

neurotoxic and nephrotoxic

active against certain GNB

24
Q

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

A

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

25
Q

susceptibility testing standards are described by the ___?

A

CLSI (clinical and laboratory standards institute)

26
Q

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

A

cation concentration
pH
thymidine
blood

27
Q

what is the standard turbidity for McFarland standards?

A

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

28
Q

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

A

macro: 1 mL

micro: 0.05 to 0.1 mL

29
Q

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

A
  • ability of test drug to diffuse through the agar
  • susceptibility of the organism to the drug
  • agar depth
30
Q

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

A

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

31
Q

Beta-lactamase is produced constantly by what five organisms?

A
  1. H. influenzae
  2. N. gonorrhoeae
  3. M. catarrhalis
  4. enterococci
  5. Bacteroides spp.
32
Q

Beta lactamase is inducible by what one spp.?

A

Staph spp.

33
Q

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

A

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

34
Q

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

A

uses phenol red

yellow = positive
red = negative

35
Q

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

A

starch-iodine

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

36
Q

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

A

Enterobacterales and nonfermenters

37
Q

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

A

MRSA

VRSA

38
Q

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

A

ampicillin

Chromogenic agars

39
Q

Strep pneumo may now have ___ resistance

A

penicillin

40
Q

what is the minimum bactericidal concentration?

A

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

41
Q

what are schlichter tests?

A

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

42
Q

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

A

is the highest serum dilution with no growth

43
Q

what is serum bactericidal titer?

A

the highest dilution that kills 99.9% of inoculum

Microbiology (13 decks)

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