MINIMUM INHIBITORY CONCENTRATION (MIC) - bacterial isolate

---

Specimen: Laboratory bacterial isolate from blood culture.

Method: Antibiotic susceptibility to a range of concentrations of an antibiotic.

Application: Treatment of streptococcal or enterococcal endocarditis.

Interpretation: The MIC is reported for a particular antibiotic 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 Streptococcus mutans with a MIC (penicillin) of >0.1 mg/L would require the addition of gentamicin to penicillin therapy. The minimum bactericidal concentration (MBC) can also be determined. The MBC is the lowest concentration which will kill >99.9% of the original inoculum of the organism. It is of dubious value in deciding antibiotic treatment.

Reference: Sherris JC and Plorde JJ. In: Sherris JC ed. Medical Microbiology. An Introduction to Infectious Diseases. 2nd ed. Prentice Hall International 1990.

---