Unit 6 abx resistance

Question 1

which elements are capable of autonomous replication. which are not

Answer 1

capable: plasmids

not capable: transposons and integrons

Question 2

role of plasmids in abx r

Answer 2

contain genes that code for virulence (antimicrobial resistance, toxins)

Question 3

role of transposable elements in abs r

Answer 3

code for recognizable phenotypic alteration e.g. antimicrobial resistance or toxin

Question 4

what are mobile resistance genes aka cassettes

Answer 4

part of an integral which must be part of chromosome, plasmid or transposon

Question 5

what info can be transferred with conjugation

Answer 5

plasmid or chromosomal genetic info

Question 6

e.g. of conjugation

Answer 6

in gram NEG donor cell a sex pilus forms allowing transfer to recipient cell

Question 7

what info can be transferred via transduction

Answer 7

bacteriophage (virus infect bacteria) takes up part of bacterial DNA and passed on

Question 8

what info can be transferred via transformation

Answer 8

uptake and recombination of donor DNA fragments. occurs on bacterial cell (host) death

Question 9

four mechanism of resistance

Answer 9

accumulation barriers, altered targets, enzymatic inactivation and bypass

Question 10

prevent drug from reaching adequate concentrations to be effective

Answer 10

what is accumulation barriers

Question 11

antimicrobial not able to bind to target site b/c changes to the target, including over production of target site

Answer 11

what is altered target

Question 12

what is enzymatic inactivation

Answer 12

antimicrobial itself is disrupted or modified

Question 13

what is bypass

Answer 13

use of diff metabolite pathway than one inhibited by drug

Question 14

compare influx accumulation barriers in Gram POS and NEG

Answer 14

gram POS thick wall impediment to some. coupled with other drugs
gram NEG OM—> LPS impedes hydrophilic molecules and porin channels impedes hydrophobic molecules, -ive charged, large molecules

Question 15

what is efflux (an accumulation barrier)

Answer 15

bacteria transport microbial out of cell using neg dependent pump

Question 16

efflux is primary defence against what

Answer 16

tetracyclines, macrocodes and other ribosomal agents

Question 17

3 ways org alter target site

Answer 17

mutation, enzymatic modification of binding site and over production of target site

Question 18

e.g. of mutation to target site

Answer 18

altered PBP gram POS is beta lactams resistance. altered peptidoglycan precursor is vancomycin resistance

Question 19

e.g. of enzymatic modification of binding site

Answer 19

methylation of ribosomal site in erm-enoded methylates and MLS

Question 20

e.g. of over production of target site

Answer 20

sulphonamide-trimethoprim group. org overproduce dihydrofolate reductase reducing effective of trimethoprim

Question 21

contrast enzymatic inactivation in β-lactamases and adenylation/acetylation/ phosphorylation

Answer 21

structural disruption destroys beta lactam ring vs. modification of active end groups

Question 22

what is bypass resistant mechanism wrt enterococci and SxT

Answer 22

enterococci resistant to SxT because folic acid pathway not required for org

Question 23

significance of intrinsic vs acquired resistance

Answer 23

unpredictable for acquired resistance.

transfer of resistance via acquired is plasmid mediated

Question 24

gram POS beta lactamases features

Answer 24

favours altered PBPs. predominantly secreted and inducible, chromosomal and bound by b-lactamse inhibitors like clavulanic acid. detection not difficult e.g. cefinase test

Question 25

gram NEG beta lactamases features

Answer 25

favours beta-lactamases production. exist in periplasmic space, inducible or constitutive, chromosomal or plasmid encoded. may or may not be bound by inhbitors

Question 26

what are ESBLs

Answer 26

extended spectrum b-lactamases
test cefoxitin: S susceptible to carbapenems
inhibited by clavulin

Question 27

what are AmpC B-lactamases

Answer 27

common: intrinsic, chromosomal, inducible gene

Question 28

PBP vs VBP

Answer 28

mecA gene found in MRSA result in production of PBP2a. altered PBP rare in gnb. VBP gene code to replace d ala d ala with d ala d lac

Question 29

why “gentamicin susceptible, amikacin resistant” are investigated

Answer 29

because it is rare. resistance pattern typically gentamicin more than amikacin

Question 30

significance of the D-test: the purpose, principle

Answer 30

resistants to clindamycin is inducible by exposure to Macrolides

Question 31

constitutive resistance to clindamycin due to erm gene means

Answer 31

organism will grow. resistant to both clindamycin and erythomycin

Question 32

what happens if clindamycin resistance is due to an inducible erm gene (iMLSB)

Answer 32

resistant to erythromycin disk and appear resistant to clindamycin (growth not inhibited) on side facing erythromycin