Antibiotic Sensitivity Flashcards
Beta lactams: penicillin/cephalosporins
inhibit cell well synthesis
- inhibit connecting peptioglycan in cell wall ; binds to penicillin binding protein and prevent penicillin binding peptidase from connecting peptidoglycan
**impact gram + more
Chloramphenicol: antimicrobial mechanism
Anti-50S: prevent protein synthesis via stopping elongation of peptide chain during protein synthesis
Aminoglycosides + tetracyclines: MoA
Anti30S: stop protein synthesis directly by causing misreading of mRNA
Quinolines + fluoroquinolones MoA
prevent DNA synthesis via inhibiting gyrase and topoisomerase (can’t unfold); this blocks DNA replication
Rifampin MoA
prevent RNA synthesis via interacting with DNA dependent RNA poly
Polymyxin B
disrupts PM - increase permeability + changes its structure
— allows more shit to get in and kill bacteria
Sulfonamides + trimethoprim: MoA
inhibit FA synthesis (impact growth and DNA synthesis)
- integrates into precursor for FA — prevents its synthesis
- prevent FA synthesis
Isoniazid MoA
inhibits mycolic acid synthesis (only in mycobacteria cell wall)
MIC
minimum conc that inhibits bacteria growth (no colonies)
MBC
minimum bacteriocidial concentration - min conc needed to kill set bacteria
** confirm : when remove drug and plate — still no growth
What is standarization and what are the aspects of testing that must be standarized?
process to minimize env. factors that could impact antimicrobial
- optimize growing conditions: ensure that any inhibition of growth is because of the antimicrobial
- optimize antimicrobial: failure to inhibit growth is a result of R
- reproducibility
** exact time (based on bacteria), concentration, total volume of dilution
Traits of Ideal Antimicrobial Agents
selective toxic
soluble in bodily fluid
non-allergenic
reasonable half life
long shelf life
inexpensive
What is selective toxicity
drug is harmful to a pathogen without being harmful to host
- relative not absolute though
Toxic SEs of Antibiotics
Drugs may be toxic to kidney, liver or nerves
- disrupt normal microbiome
Broad spectrum
Work on a large range of bacteria
- more likely to have off target effects that disrupt microbiome
Narrow spectrum antibiotics
increased selection, reduced non-selective toxicity
Bacteriocidal vs Bacteriostatic
Bacteriocidal - kills bacteria, can be bacteriostatic at low concentrations
Bacteriostatic: stops bacteria growth when present, bacteria growth continues once it is removed; requires the host immune system to kill the bacteria
What are the convenient susceptibility tests for measuring antimicrobial activity
disk diffusion
broth dilution
agar dilution
Limits of standardization
can’t reproduce in vivo environment - aka where antibiotic and bacteria actually interact
- factors that may impact outcome that aren’t accounted for in testing: diffusion into tissue/host cell, serum protein binding, immune system status, and virulence
What is broth dilution testing
Range of concentrations of antimicrobial are examines in series of doubling dilutions (log 2)
- look at difference concentrations: determined based off the safest therapeutic concentration possible, level needed to detect R
- can help get MIC: first clear tube seen
—- MIC than translated to susceptible, intermediate, or resistant category based on past studies
Macro vs micro dilution
macro - 2mL
micro - 100 uL (normally on 96 well plate; more efficient)
Advantages and Disadvantages of broth dilution testing
Advantages: quantitative, simple, easy to reproduce, could automate
Negatives: time consuming, tedious, uses a lot of media, possibility for human error
What is agar dilution testing
serial dilutions of antibiotic is added to melted media and solidified (plates with different concentrations)
- fixed number of organisms are then plated onto each plates (as dots); incubate and examine for colony growth
MIC - first plate with no colony growth
Advantages and Disadvantages of agar dilution testing
Advantage: more gradual changes
Disadvantages: labour intensive, expensive and takes a lot of space
