Antimicrobial Resistance Flashcards
define antimicrobial resistance
ability of microbes to resist whatever is trying to kill them
three major purposes of antiicrobial prescription
therapeutics – treat sick individual
metaphylactics – treat herd when one sick individual
prophylactics – seasonal treatment
growth promotion – banned in many places
what leads to AMR bacteria spread
unregulated use of anitmicrobials
use of contaminated feces or water in fertilizer
contaminated food or water
classical gram positive cell wall architecture
several layers of peptidoglycan with lipo/teichoic acid
mycobacterium cell wall architecture
peptidoglycan covered by mycolic acids (wax or lipids)
classical gram negative cell wall architecture
outer membrane of proteins and lipopolysaccharaides (lipid A and sugar or endotoxin) that hides peptidoglycans
thin layer of peptidoglycans
chlamydia cell wall architecture
cell wall without peptidoglycans
outer membrane with proteins and lipopolysaccharides (lipid A and sugar or endotoxin)
mycoplasma cell wall architecture
no cell wall
sterols in cell membrane
not stained by gram stain
resistant to antimicrobials acting on cell wall
porins
antimicrobials, nutrients, mineral go through these
biofilms
dense bacteria community
6 mechanisms of action of antimicrobials
-cell wall synthesis – B lactams deactivate cell wall synthesis enzymes
-metabolism – folic acid synthesis
-30S – protein syntehsis
-50S – protein syntehsis
-RNA polymerase – mRNA (RNA synthesis)
-DNA gyrase/topoisomerase (DNA syntehsis)
4 mechanisms of AMR
-reduced permeability – constrict porins so antimicrobials can’t enter
-efflux pumping (“vomiting”)
-drug inactivation by enzymes – cut antimicrobials
-target site change, modification, protection
what is an additional mechanism of AMR in addition to main 4
biofilm formation
biofilm characteristics
-induced extracellular polymer (matrix)
-low nutrient and oxygen supply to center
-dormant spore like cells in center for persistence
acquired resistance
-horizontal gene transfer
-free DNA transformation
-plasmid conjugation
-bacteriophage transduction
intrinsic (innate) resistance
-vertical gene transfer
-mycoplasma
grow fast in 24 hours
-enterobactericeae
-gram negative bacilli
-non fastidious gram positive
do not grow fast in 24 hours
-fastidious organisms
-bioterrorism agents
-anaerobic microbes
ESKAPE
E – Enterococcus
S – Staphylococcus aureus
K – Klebsiella pneumoniae
A – Acinetobacter baumannii
P – Pseudomonas aeruginosa
E – Enterobacter
isolation using bacterial cell culture media
-mannitol salt agar – Staphylococcus, Enterococcus, Listeria, Micrococcaceae
-Edward media – Streptococcus, Enterococcus
-Kenner fecal agar – Enterococcus
-MacConkey agar – Enterobacteriaceae, Enterococcus
media for anaerobic bacteris
-broth – Brucella + hemin, vitamin K, lysed horse blood
-agar – Brucella blood agar + hemin, vitamin K, lysed horse blood
media for aerobic bacteria
-broth – cation adjusted Mueller Hinton + lysed horse blood
-agar – cation adjusted Mueller Hinton + lysed horse blood
disc diffusion for AMR detection
-solid media
-qualitative
-one disc represents one drug
-measure diameter of inhibition zone
E test AMR detection
-solid media
-quantitative
-strip impregnated with drug
-MIC – minimum inhibitory concentration
-determine last concentration that inhibited growth
agar dilution AMR detection
-solid media
-quantitative
-drug added to culture media
-between concentrations of 0.12 to 64 ug/mL
macrodilution AMR detection
-liquid media
-quantitative
-determine last dilution that inhibited growth
-bacterial growth indicated by cloudiness
microdilution AMR detection
-liquid media
-quantitative
-96 well plate with serially diluted in increased 2 fold concentrations of antimicrobial agents
-determine last dilution to inhibit growth
-growth indicated by dot of organismal growth
what do guidelines instruct to include and why
genetically stable known reference bacteria strains
quality control
quality control for B lactamase producing bacteria
E coli
K pneumoniae
A bacumannii
quality control for nonfastidious bacteria for agar/broth dilution (MIC)
E coli
P aeruginosa
E faecalis
S aureus
quality control for testing bacteria of bioterrorism
E coli
S aureus
why would testing be invalidated
-no viable or pure growth of quality control strains
-cut off value inhibition zone by disc or MIC not within range defined by CLSI, EUCAST, ISO
what are MIC cut off values for most antimicrobials
0.5 to 64 ug/mL
steps of disc diffusion test protocol
- McFarland standards = 0.5
- 1-2x10^8 CFU/mL; rotate and press against glass
- 4mm thick MH agar
- rotate in 3-4 directions by swabbing each time
- rim swab around entire edge of plate
- 6mm diameter disc; place disc >24 mm from each other
- incubate
- measure inhibition zones
control of fast spreading AMR
-surveillance – periodic survey of drug use pattern
-educate expertise for reducing drug use
-regulate, monitor, and evaluate is frug use is per set priority
what can bacteria acquire AMR genes form
plasmid
phage
free DNA
parents
AMR can be controlled by what broad interventions
-judicious drug use
-surveillance
-diagnosis
-discoveries
-collaborations
-policy and practice changes
