Excercise 7-3 Micro Lab: Antimicrobial Susceptibility Test
natural antimicrobial agents produced by microorganisms
antimicrobials or antimicrobics
all substances used to treat bacterial infections
Kirby Bauer test
also called the disk diffusion test, it measures the effectiveness of antimicrobics against pathogenic microorganisms
How does the Kirby Baur test work?
antimicrobic impregnated paper discs are placed that is inoculated to form a bacterial lawn. the plates are incubated and upon being taken out, if the organism is susceptible to the drug, it will form a zone of inhibition
zone of inhibition
clear zone around the disk where growth has been inhibited
drugs that kill the organism
drugs that stop growth but don't kill the microbe
What is the depth that Kirby Bauer agar is poured and why is it so important the depth?
4mm deep in either a 150mm or 100mm petri dish
depth is important of its effect on diffusion. thick agar slows lateral diffusion and thus produces smaller zones than plates held to the 4mm standard
What kind of agar is used in Kirby Bauer method?
Mueller Hinton agar with a pH of 7.2 to 7.4
In Kirby Bauer method, the broth is diluted to match the _____ turbidity in the McFarland standard before inoculating the plate
How long are the discs containing the antimicrobial agent incubated in the Kirby Bauer method?
16 to 18 hours at 2 degrees Celsius
antimicrobial susceptibility testing
used to measure the effectiveness of antibiotics and other chemotherapeutic agents on pathogenic organisms
how does the antibiotic chloramphenicol work?
prevents peptide bond formation during translation
how does the antibiotic ciprofloxacin work?
interferes with DNA replication
how does the antibiotic trimethoprim work?
inhibits purine and pyrimidine synthesis
how does the antibiotic penicillin work?
inhibits cross linking of the cell wall's peptidoglycan
Bacterial resistance mechanisms to antibiotics can be broken down into three main types:
1. altered target such as antibiotic can no longer interact with cellular process
2. an alteration in how the drug is taken into the cell
3. enzymatic destruction of drug