bactitech
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Another question:
The breakpoint of an antimicrobial drug refers to:
a. The amount needed to cause bacteriostasis
b. A minimum inhibitory concentration of 16 ug/ml or greater
c. A minimum inhibitory concentration of 64 ug/ml or greater
d. The level of drug that is achievable in serum
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| kkr
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is it A?
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| bactitech
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No.  Try again.
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| ssrpk
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i am sure it's either b or c ...... but shud'nt tht value be diferent for different antimicrobials!
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| bactitech
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Actually, the answer is D. From my key:
"The breakpoint refers to an antimicrobial concentration in the serum with optimal therapy usually expected with frequently used dose schedules. An organism is susceptible if the minimum inhibitory concentration (MIC) is at or below the breakpoint."
Susceptibility results (at our lab) are reported with the MIC and the interpretation of that MIC for that drug. We use automated susceptibilties for most common organisms. Occasionally we must use disc diffusion testing, so the MIC in that case is not reported - just S/I/R (susceptible/intermediate/resistant).
Occasionally the infectious disease docs will order SIC/SBC levels on patients that aren't improving. (SIC=serum inhibitory concentration; SBC=serum bactericidal concentration). We grow up the patient's organism in the lab to get fresh growth. The patient is drawn right before their antibiotic dosing, and again at the peak after dosing - usually an hour or so after an IV drug. Their serum is brought down to the lab. Serial dilutions of the patients serum are made aseptically starting with 1:1, 1:2, 1:4, 1:8, etc. in sterile saline. Then a dilution of the patients organism (sorry I can't remember the dilution factor) is added to each tube and incubated overnight. The SIC is the first visually clear tube. Then the clear tubes are subcultured with a calibrated loop (can't remember which one now) and incubated overnight again. The first tube with NO organisms growing is the SBC (serum bactericidal level). This is the level at which the organism is actually killed off. The SIC is not necessarily the SBC. There's usually a couple of tubes different. I think the ID docs aim for an SIC of around 1:4 but I'm not sure - they don't run them very often and it's been too long since I've done one.
The MIC is the minimum level of antibiotic needed to inhibit the growth of bacteria. The MBC is the minimum level of antibiotic needed to kill the bacteria. This page gives a decent discussion on this complicated subject.
http://pathmicro.med.sc.edu/mayer/antibiot.htm
This is pretty in-depth, and not in the best format, but gives lots of information also:
http://www.escmid.org/Seviware/Script/SvFiles.asp...
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Clinical Microbiology since 1974
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| ssrpk
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hey!tht's a very cool info!
thnx a lot 
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