Unit 6 abx resistance Flashcards
which elements are capable of autonomous replication. which are not
capable: plasmids
not capable: transposons and integrons
role of plasmids in abx r
contain genes that code for virulence (antimicrobial resistance, toxins)
role of transposable elements in abs r
code for recognizable phenotypic alteration e.g. antimicrobial resistance or toxin
what are mobile resistance genes aka cassettes
part of an integral which must be part of chromosome, plasmid or transposon
what info can be transferred with conjugation
plasmid or chromosomal genetic info
e.g. of conjugation
in gram NEG donor cell a sex pilus forms allowing transfer to recipient cell
what info can be transferred via transduction
bacteriophage (virus infect bacteria) takes up part of bacterial DNA and passed on
what info can be transferred via transformation
uptake and recombination of donor DNA fragments. occurs on bacterial cell (host) death
four mechanism of resistance
accumulation barriers, altered targets, enzymatic inactivation and bypass
prevent drug from reaching adequate concentrations to be effective
what is accumulation barriers
antimicrobial not able to bind to target site b/c changes to the target, including over production of target site
what is altered target
what is enzymatic inactivation
antimicrobial itself is disrupted or modified
what is bypass
use of diff metabolite pathway than one inhibited by drug
compare influx accumulation barriers in Gram POS and NEG
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
what is efflux (an accumulation barrier)
bacteria transport microbial out of cell using neg dependent pump
efflux is primary defence against what
tetracyclines, macrocodes and other ribosomal agents
3 ways org alter target site
mutation, enzymatic modification of binding site and over production of target site
e.g. of mutation to target site
altered PBP gram POS is beta lactams resistance. altered peptidoglycan precursor is vancomycin resistance
e.g. of enzymatic modification of binding site
methylation of ribosomal site in erm-enoded methylates and MLS
e.g. of over production of target site
sulphonamide-trimethoprim group. org overproduce dihydrofolate reductase reducing effective of trimethoprim
contrast enzymatic inactivation in β-lactamases and adenylation/acetylation/ phosphorylation
structural disruption destroys beta lactam ring vs. modification of active end groups
what is bypass resistant mechanism wrt enterococci and SxT
enterococci resistant to SxT because folic acid pathway not required for org
significance of intrinsic vs acquired resistance
unpredictable for acquired resistance.
transfer of resistance via acquired is plasmid mediated
gram POS beta lactamases features
favours altered PBPs. predominantly secreted and inducible, chromosomal and bound by b-lactamse inhibitors like clavulanic acid. detection not difficult e.g. cefinase test
gram NEG beta lactamases features
favours beta-lactamases production. exist in periplasmic space, inducible or constitutive, chromosomal or plasmid encoded. may or may not be bound by inhbitors
what are ESBLs
extended spectrum b-lactamases
test cefoxitin: S susceptible to carbapenems
inhibited by clavulin
what are AmpC B-lactamases
common: intrinsic, chromosomal, inducible gene
PBP vs VBP
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
why “gentamicin susceptible, amikacin resistant” are investigated
because it is rare. resistance pattern typically gentamicin more than amikacin
significance of the D-test: the purpose, principle
resistants to clindamycin is inducible by exposure to Macrolides
constitutive resistance to clindamycin due to erm gene means
organism will grow. resistant to both clindamycin and erythomycin
what happens if clindamycin resistance is due to an inducible erm gene (iMLSB)
resistant to erythromycin disk and appear resistant to clindamycin (growth not inhibited) on side facing erythromycin
