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Comparative evaluation of penicillin, ampicillin, and imipenem MICs and susceptibility breakpoints for
1Departments of Medicine and Pathology, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901-0019, USA. weinstei@umdnj.edu
Abstract:
Although imipenem has in vitro activity against Enterococcus faecalis and Food and Drug Administration-approved indications for treatment of infections caused by this microorganism, there are no NCCLS guidelines for susceptibility testing of imipenem versus enterococci. Therefore, the in vitro activities of penicillin, ampicillin, imipenem, and vancomycin against 201 blood isolates of E. faecalis and 24 blood isolates of Enterococcus faecium were compared. The susceptibility of isolates to penicillin or ampicillin accurately predicted the in vitro activity of imipenem. Since the susceptibility of enterococci to imipenem can be predicted by the results obtained by testing of penicillin or ampicillin, testing of imipenem by clinical laboratories probably is not necessary.
Insights
Testing imipenem susceptibility against Enterococcus species is not necessary. Penicillin or ampicillin susceptibility accurately predicts imipenem activity, simplifying clinical laboratory testing for enterococcal infections.
Area of Science:
- Microbiology
- Clinical Infectious Diseases
- Antimicrobial Resistance
Background:
- Imipenem exhibits in vitro activity against Enterococcus faecalis.
- The Food and Drug Administration has approved imipenem for treating infections caused by Enterococcus species.
- Current National Committee for Clinical Laboratory Standards (NCCLS) guidelines lack recommendations for imipenem susceptibility testing in enterococci.
Purpose of the Study:
- To compare the in vitro activities of penicillin, ampicillin, imipenem, and vancomycin against clinical isolates of Enterococcus faecalis and Enterococcus faecium.
- To determine if penicillin or ampicillin susceptibility testing can predict imipenem activity in enterococci.
Main Methods:
- In vitro susceptibility testing was performed on 201 blood isolates of E. faecalis and 24 blood isolates of E. faecium.
- The study compared the efficacy of penicillin, ampicillin, imipenem, and vancomycin against these enterococcal isolates.
Main Results:
- Susceptibility of enterococcal isolates to penicillin or ampicillin accurately predicted their in vitro susceptibility to imipenem.
- A strong correlation was observed between penicillin/ampicillin resistance and imipenem resistance.
Conclusions:
- Clinical laboratories can reliably predict imipenem susceptibility in enterococci by performing susceptibility tests for penicillin or ampicillin.
- Routine susceptibility testing of imipenem against enterococci is likely unnecessary, streamlining clinical diagnostics.