Minimum inhibitory concentration (MIC) - bacterial isolate

Last updated: Tuesday, 07, August, 2007

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Item Process
Specimen

Laboratory bacterial isolate.

Method

Antibiotic susceptibility to a range of concentrations of an antibiotic by broth dilution, including microbroth dilution in commercial systems.

E-test.

Application

Susceptibility testing of streptococcal or enterococcal isolates causing endocarditis;
testing of penicillin-resistant Streptococcus pneumoniae, especially in the context of meningitis;
testing of isolates for which interpretation criteria have not been published for routine test methods (eg, for certain antibiotics and Helicobacter pylori).

Interpretation

The MIC of a particular antibiotic is reported in mg/L.

The MIC is the lowest concentration of antibiotic which inhibits the growth of the bacterium.

In patients with endocarditis the test helps to determine whether a second antibiotic should be added (eg, for a MIC of penicillin for Streptococcus mutans  of >0.1 mg/L,  the addition of gentamicin to penicillin therapy is indicated).

Reference

Peterson LR and Collins SM. Clin Microbiol Newslett 2000; 22: 153-157.