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Medical and general microbiology > antibiotic resistance > Flashcards

antibiotic resistance Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

what is resistance

A

antimicrobial reisstance is resistance of a microorganism to an antimicrobial drug that was originally effective for treatment of infections caused by it

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2
Q

MIC

A

minimum inhibitory concentration

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3
Q

how does one measure resistance

A

typically reflected as an increase in the MIC f a drug

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4
Q

minimum inhibitory concentration

A

lowest conc at which an antimicrobial will inhibit the visible growth of a microorganism after overnight incubation
–> reflected as a increase in the MIC

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5
Q

in MIC experiment a clear well indicates

A

inhibition of growth

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6
Q

in a cloudy well

A

indicates growth

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7
Q

MBC

A

minimum bactericidal concentration- the lowest con at which an antimicrobial kills in vitro

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8
Q

how can we correlate these values with what is used in the clinic

A

use of breakpoints

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9
Q

breakpoitns

A

is a chosen conc of an antibiotic which defines whether a species of bacteria is susceptible or resistant to the antibiotic If the MIC is less than or equal to the susceptibility breakpoint the bacteria is considered susceptible to the antibiotic.

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10
Q

if the MIC is bigger than the breakpoint

A

bacteria is intermediate or resistant to the antibiotic

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11
Q

bacteriostatic agents

A

reaches MIC levels in blood/tissues

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12
Q

bactericidal agents

A

reaches tidal levels in blood/tissues

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13
Q

broad spectrum agent

A

low MICs for many diff material tyoes

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14
Q

narrow spectrum agent

A

low MICs for just a few bacterial types

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15
Q

susceptible (sensitive) microbe

A

inhibited by an agent at low MIC

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16
Q

resistant microbe

A

inhibited by an agent only at a high MIC

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17
Q

generally across the country there is a real concern with

A

bacterial resistance, where some antibiotics like cephalosporins and fluorquinolones in the treatment of UTIs show 50% resistance or more in 5/6 regions.

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18
Q

mechanisms of resistance (4)

A

(1) drug inactivation uses enzymes that modify the drug
(2) alteration of the drug target site prevents the drug from binding to its target
(3) drug inaccessibilityy preventing entrance of the drug into the cell by modifying membrane permeability or transport systems
(4) drug efflux pumps the drug out of the cell using pumps

19
Q

why is S.aureus resistant to penicillin

A

due to the presence of penicillinase

20
Q

antibiotic resistant genes are present on

A

chromosomes and plasmids

21
Q

how is antibiotic resistance transferred

A

vertical and horizontal transmission

22
Q

why is use of antibiotics selecting for resistance

A

-can provide a selection pressure, meaning evolution and spread of antibiotic resistance genes

23
Q

modification of antibiotics by enzymes :MRSA

A

staphylococcal cassette chromosome- mec(SSCmec) . Each SCCmec element carries a cassette chromosome recombinase and mic gene complex. mecA codes for a variant penicillin binding protein with a lower affinity for B-lacams- resulting in resistance to virtually all available B-lactam drugs.

24
Q

streptomycin is an

A

aminoglycoside

25
Q

modifications of antibiotics by enzymes: streptomycin

A

protein synthesis inhibitor - targets 30s subunit- produced by Streptomycin app. Modified by phosphotransferase.

26
Q

other resistance mechanism of streptomycin

A

chromosomal acquired streptomycin resistance is due to mutations in the gene encoding the ribosomal protein s12

27
Q

man-made chloraemphenicol

A

protein synthesis inhibitor- targeting the 30s subunit- modified by acetylation.

-another resistance mechanism- chromosomal ended cmlA appears to produce more OmpaA leading to reduced permeably leading to chloramphenicol resistance- mutations in 50 subunit genes are rare.

28
Q

drug efflux pumps are present in

A

both gram negative and positive bacteria except the RNS family

29
Q

drug efflux pump: e.coli

A

A crAB-TolC has been shown to extrude chloramphenicol, fluorquinolones, tetracycline. novobiocin and b.lactam antibiotics

30
Q

drug efflux pumps: s.typhimurim

A

the AcrAB-TolC efflux system expels quinolone, chloramphenicol, tetracycline and nalidixic acid

31
Q

major mediators of resistance to tetracycome

A

protein synthesis inhibitor- targeting 30s subunit

32
Q

natural transformation

A

uptake of DNA from medium- mediated by competence proteins

33
Q

which species does natural transformation take place

A

Bacillus, Streptoccocus, Haemophilus, Neiserria

34
Q

conjugation

A

the resistance gene moves wit the replicating plasmid i into a new cell

35
Q

transduction

A

the resistance gene is integrated into the new host cell chromosome or plasmid along with phage DNA

36
Q

resistant cells have a selective advantage because

A

the antibiotics wipe out all competition for resistant cells, so can proliferate

37
Q

vertical transmission

A

resistance is passed down via mitosis

38
Q

horizontal gene transfer

A

transfer of genetic material between mature cells

39
Q

which is the main reason or antibiotic resistance

A

horizontal gene transfer

40
Q

there mechanisms of horizontal gene transfer

A

transformation, transduction, conjugation

41
Q

which stapholoccus gene is responsible for MRSA

A

SSCmec- which sequence includes the mecA gene

42
Q

mecA

A

gene found in staph which codes for resistance to methicillin. The only known method of how staph spreads this gene is via horizontal transmission

43
Q

What does mecA code for?

A

codes for a variant penicillin binding protein with a lower affinity for B-lacams- resulting in resistance to virtually all available B-lactam drugs.

Medical and general microbiology (36 decks)

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