Lec 5 Flashcards
Primary goal of antimicrobial susceptibility testing
Determine whether the bacterial isolate is capable of expressing resistance of the therapeutic antimicrobial agents
Universally susceptible to penicillin
Group A b-hemolytic Streptococcus
The drug of choice in treating infections caused by this bacterium
Penicillin
Grown directly from agar plates to match the turbidity of the 0.5 McFarland Standard
Pure culture
Newly inoculated bacterial suspension and McFarland standard are compared against?
Dark background
The turbidity of the bacterial suspension should be the same as that of the McFarland standard (true or false)
True
Occur if too few bacteria are tested
False-susceptible results
Outcome of testing too many bacteria
False-resistant results
Most widely used method of inoculum standardization
McFarland turbidity standard
Most commonly used McFarland turbidity standard
McFarland 0.5 standard which contains 99.5 mL of 1% sulfuric acid and 0.5 mL of 1.175% barium chloride
Convenient and more precise alternative to visual adjustment to match the McFarland standard
Nephelometric or spectrophotometric
Antimicrobial agents chosen for testing against a particular bacteria isolate
Antimicrobial battery or panel
Publishes up-to-date tables listing potential antimicrobial agents
Clinical and Laboratory Standards Institute
Uses a liquid medium
Broth dilution
Total broth volume of macrodilution
1mL or greater
Need multiple large test tubes, thus the test is rarely used because it is cumbersome and labor intensive
Macrodilution
Total broth of microdilution
0.05 to 0.1 mL
Accomplished in a single microtiter tray
Microdilution
More commonly used broth dilution
Microdilution
No antimicrobial agent is added
Growth control
Not inoculated in bacterial suspension
Sterility control
In the broth dilution, trays are incubated at?
35degree C for 16 to 20 hours
Antimicrobial agent in question may be an appropriate choice for treating the infection caused by the organism
Susceptible
Not inhibited with serum-achievable levels of the drug
Resistant
Tube color that signify growth
Green
Tube color that signify no growth
Pink
Uses agar-based medium
Agar dilution method
Allows examination of one or more
Agar dilution method
Disadvantage of agar dilution method
Labor insensitive, not commonly used
Referred as the Kirby Bauer method
Disk diffusion method
