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Investigation of imipenem efficacy against carbapenem-susceptible but heteroresistant Acinetobacter baumannii clinical isolates by experimental pneumonia

Abstract number: R2250

Michail G., Ikonomidis A., Neou E., Maniatis A., Pournaras S.

Objectives: The clinical consequences of the recently described carbapenem heteroresistance of Acinetobacter baumannii remain unknown. The aim of this study was to investigate the efficacy of imipenem treatment against apparently carbapenem-susceptible, heteroresistant Acinetobacter baumannii clinical isolates by experimental infection model.

Materials: The study included four previously characterised A. baumannii clinical isolates: one apparently carbapenem-susceptible A. baumannii exhibiting unstable carbapenem heteroresistance, one with stable heteroresistance, one carbapenem-susceptible without heterogeneity and one carbapenem-resistant. Approximately 107 CFUs of the isolates were inoculated intratracheally to cause experimental pneumonia in Wistar rats. The animals were treated with 30 mg/kg body weight imipenem/cilastatin intraperitoneally q. 6 h for 24 h, sacrificed, the lungs excised and homogenised and cultured with serial dilutions, to estimate the bacterial counts yielded. Equal numbers of animals remained untreated as controls of the experimental infection.

Results: No bacterial growth was observed from the animals that were infected by the two carbapenem-heteroresistant isolates and the susceptible A. baumannii and treated with imipenem. The carbapenem-resistant isolate yielded approximately 100 CFU/ml of the lung homogenate after imipenem treatment. All isolates were grown from the lungs of the untreated animals, in numbers ranging from 13 x 103 to 125 x 103 CFUs/ml, assuring the success of the experimental infection.

Conclusions: The results of the present study indicate that the heteroresistant A. baumannii isolates tested may be treated with equal success as susceptible ones, with the administration of adequate imipenem dosing regimens.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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