mechanism of resistance to antibiotics Flashcards
3 types of resistance
intrinsic
mutational
acquired
intrinsic/natural resistance
innate ability of bacteria to resist activity of a particular antimicrobial agents through is inherent structural or functional characteristics
mutational resistance
due to spontaneous or random mutation
can occur due to exposure to an antibiotic
will depend on structure and # of genes in which mutations can produce selectable phenotype
acquired resistance
occurs when organism obtains to ability to resist the activity of a particular antibiotic in which it was previously susceptible
can occur through horizonal gene transfer
location of antimicrobial resistant genes
- plasmids
2. transposable genetic elements- transposable genetic elements and insertion sequences
can transpoons replicate on their own?
can plasmids?
transpoons cannot
plasmids can
how do transpoons and insertion sequences differ?
transpoons encode functional genes that mediate a recognizable phenotype (such a antibiotic resistance)
insertion sequences only encode functions involved in insertion events (can contain partial or complete promoter sequences)
what are integrons
dna adjacent to antibiotic resistance genes who often have unique integration units called integrons
principal role of integrons
provide a convenient insertion site for antibiotic resistance genes from foreign DNA sources
the frequency of transcription of integrated cassettes of antibiotic resistance genes depends on?
proximity of the gene to the promoter at the 5` upstream end of the integron
what effects the level of expression of a resistance gene?
the distance between the promoter and the specific antibiotic-resistance gene cassette
(level of expression and distance inversely proportionate)
list 8 mechanisms in which antibiotic resistance is described in bacteria
enzymatic inactivation decreased permeability efflux alteration of target site protection of target site overproduction of target bypass inhibited process binding of antibiotic
enzyme inactivate example and mechanism
B- lactamases- enzymes that inactivate antibiotics by splitting the amide bond of B-lactam ring
what are extended spectrum B-lactamases and what 3 pathogens are the usually associated with
enzymes that mediate resistance to extended spectrum (3rd generation) antibiotics
found on klebsiella, e. coli and proteus
patients who exhibit what type of B lactamase is place in isolation like MRSA
extended spectrum
carbapenemases can hydrolyze which antibiotics
carbapenems and also broad spectrum penicillins, oxymino-cephalosporins and cephamycins
how can you treat an infection due to a beta lactamase producing organism with a beta lactam based antibiotic?
- penicillin resistant penicillins
- b- lactamase inhibitors and inhibitor combinations
- extended spectrum cephalosporins and carbapenams
how does altering the target site increase antibiotic resistance
ex. alteration of ribosomal binding sites causes a failure of the antibiotic to bind to its target site on the ribosome and disrupts it ability to inhibit protein synthesis and cell growth
ex2. alteration of cell wall precursor sites
ex3. alteration of target enzymes (MRSA!)
how does the bypass of antibiotic inhibition target lead to antibiotic resistance?
by developing auxotrophs which have diff growth factor requirements than wild type
mechanism of resistance for VRE
alteration of cell wall precursor target sites
what are most common organisms that have amp C B-lactamases?
observed in enterobacteriaceae other than klebsille and e coli
plasmid mediated ampC enzymes on E. coli, K. pneumoniae, salmonella enterica and proteus mirabilis
where are carbapenemases seen?
on k. pneumoniae
