antibiotic resistance

Question 1

what is resistance

Answer 1

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

Question 2

MIC

Answer 2

minimum inhibitory concentration

Question 3

how does one measure resistance

Answer 3

typically reflected as an increase in the MIC f a drug

Question 4

minimum inhibitory concentration

Answer 4

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

Question 5

in MIC experiment a clear well indicates

Answer 5

inhibition of growth

Question 6

in a cloudy well

Answer 6

indicates growth

Question 7

MBC

Answer 7

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

Question 8

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

Answer 8

use of breakpoints

Question 9

breakpoitns

Answer 9

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.

Question 10

if the MIC is bigger than the breakpoint

Answer 10

bacteria is intermediate or resistant to the antibiotic

Question 11

bacteriostatic agents

Answer 11

reaches MIC levels in blood/tissues

Question 12

bactericidal agents

Answer 12

reaches tidal levels in blood/tissues

Question 13

broad spectrum agent

Answer 13

low MICs for many diff material tyoes

Question 14

narrow spectrum agent

Answer 14

low MICs for just a few bacterial types

Question 15

susceptible (sensitive) microbe

Answer 15

inhibited by an agent at low MIC

Question 16

resistant microbe

Answer 16

inhibited by an agent only at a high MIC

Question 17

generally across the country there is a real concern with

Answer 17

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

Question 18

mechanisms of resistance (4)

Answer 18

(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

Question 19

why is S.aureus resistant to penicillin

Answer 19

due to the presence of penicillinase

Question 20

antibiotic resistant genes are present on

Answer 20

chromosomes and plasmids

Question 21

how is antibiotic resistance transferred

Answer 21

vertical and horizontal transmission

Question 22

why is use of antibiotics selecting for resistance

Answer 22

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

Question 23

modification of antibiotics by enzymes :MRSA

Answer 23

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.

Question 24

streptomycin is an

Answer 24

aminoglycoside

Question 25

modifications of antibiotics by enzymes: streptomycin

Answer 25

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

Question 26

other resistance mechanism of streptomycin

Answer 26

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

Question 27

man-made chloraemphenicol

Answer 27

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.

Question 28

drug efflux pumps are present in

Answer 28

both gram negative and positive bacteria except the RNS family

Question 29

drug efflux pump: e.coli

Answer 29

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

Question 30

drug efflux pumps: s.typhimurim

Answer 30

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

Question 31

major mediators of resistance to tetracycome

Answer 31

protein synthesis inhibitor- targeting 30s subunit

Question 32

natural transformation

Answer 32

uptake of DNA from medium- mediated by competence proteins

Question 33

which species does natural transformation take place

Answer 33

Bacillus, Streptoccocus, Haemophilus, Neiserria

Question 34

conjugation

Answer 34

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

Question 35

transduction

Answer 35

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

Question 36

resistant cells have a selective advantage because

Answer 36

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

Question 37

vertical transmission

Answer 37

resistance is passed down via mitosis

Question 38

horizontal gene transfer

Answer 38

transfer of genetic material between mature cells

Question 39

which is the main reason or antibiotic resistance

Answer 39

horizontal gene transfer

Question 40

there mechanisms of horizontal gene transfer

Answer 40

transformation, transduction, conjugation

Question 41

which stapholoccus gene is responsible for MRSA

Answer 41

SSCmec- which sequence includes the mecA gene

Question 42

mecA

Answer 42

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

Question 43

What does mecA code for?

Answer 43

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