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[Comparative activity of imipenem, ceftazidime and cefotaxime against Acinetobacter calcoaceticus]
E Vallée1, M L Joly-Guillou, E Bergogne-Berezin
1Service de Microbiologie, CHU Xavier-Bichat, Paris.
Abstract:
The authors compared the in vitro activity of imipenem, ceftazidime and cefotaxime against 100 strains of Acinetobacter calcoaceticus isolated in 1986 and 1987. The minimal inhibitory and bactericidal concentrations (MICs and MBCs) were determined by the agar dilution and broth microdilution methods respectively, with and without 50 per cent of human serum in the medium to evaluate the possible influence of protein binding. Imipenem was the most active of the three drugs against Acinetobacter, including beta-lactamase producing strains. The MICs 50 and 90 of imipenem were 0.18 micrograms/ml and 0.48 micrograms/ml respectively, as opposed to 5.16 and 14.61 micrograms/ml for ceftazidime, 16 and 75.6 micrograms/ml for cefotaxime. No change was noted in the susceptibility of Acinetobacter to imipenem from 1981 to 1987. The geometric mean MIC of imipenem was 0.25 micrograms/ml. Susceptibility remained unchanged for ceftazidime and cefotaxime but the geometric mean MICs were higher, being 7.29 and 22.8 micrograms/ml respectively. Imipenem had the highest bactericidal activity, with a mean MBC/MIC ratio of 1.16. The presence of human serum did not influence the results, due to the low protein binding of all three antibiotics. It is concluded that imipenem is one of the major antibiotics available for the treatment of nosocomial Acinetobacter infections. However, a few resistant strains have recently been isolated, confirming the need for epidemiological surveillance of bacterial resistance to this antibiotic.
Insights
Imipenem demonstrated superior in vitro activity against Acinetobacter calcoaceticus compared to ceftazidime and cefotaxime. Ongoing surveillance is crucial due to emerging imipenem resistance in nosocomial infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Acinetobacter calcoaceticus is a significant cause of nosocomial infections.
- Understanding antibiotic susceptibility is critical for effective treatment.
- Carbapenems, like imipenem, are often used for multidrug-resistant Gram-negative bacteria.
Purpose of the Study:
- To compare the in vitro activity of imipenem, ceftazidime, and cefotaxime against Acinetobacter calcoaceticus.
- To assess the impact of human serum on antibiotic activity.
- To evaluate trends in antibiotic susceptibility over time.
Main Methods:
- In vitro susceptibility testing using agar dilution and broth microdilution methods.
- Determination of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs).
- Testing was performed with and without 50% human serum to evaluate protein binding effects.
Main Results:
- Imipenem exhibited the highest in vitro activity against Acinetobacter strains, including beta-lactamase producers.
- MIC50 and MIC90 values for imipenem were significantly lower than for ceftazidime and cefotaxime.
- No significant change in imipenem susceptibility was observed between 1981 and 1987; however, emerging resistance necessitates surveillance.
Conclusions:
- Imipenem is a key antibiotic for treating nosocomial Acinetobacter infections.
- Low protein binding of the tested antibiotics minimizes serum influence on activity.
- Continuous epidemiological surveillance is essential to monitor and address the emergence of antibiotic resistance.