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Biological cost of resistance to carbapenems in a Klebsiella pneumoniae isolate

Abstract number: P1701

González-Torralba A., Martín-Díaz A., Alós J.I.

Carbapenems (imipenem, meropenem, ertapenem) are bactericidal antibiotics that acts by inhibiting the bacterial cell wall, and which are used mainly in the treatment of severe infections. Resistance to carbapenems are exceedingly rare in Enterobacteriaceae despite its frequent use since long time ago. The objective of this study was to ascertain whether a strain of K. pneumoniae resistant to carbapenems have less fitness than those that are carbapenem-sensitive in competing, and would therefore tend to disappear in their competition with carbapenem-sensitive strains in the absence of antibiotics.

Methods: One carbapenem-resistant strain and six carbapenem-sensitive strains of K. pneumoniae.

Thirty competition experiments by pairs of strains were conducted, 5 by each sensitive strain (carbapenem-R versus carbapenem-S). The experiments were performed in nutrient broth (NB). Equal amounts of the strains were challenged (approx. 50% and approx. 50%) for 5 days, with a daily change to a new medium. Six differential counts were performed (days 0, 1, 2, 3, 4 and 5). For the differential counts on the fifth day, MacConkey agar with and without ertapenem (2 mg/L) and a replica plater machine were used.

The mean of results for each pair of strains and the range, in parenthesis, are presented below.

Results: In all the pair experiments there were a relative increase in the carbapenem-sensitive strain that translated into a count of 76% (63–90%), 94% (90–98%), 80% (71–95%), 93% (78–99%), 83% (78–89%), and 95% (89–98%) on the fifth day.

Conclusions:

•Resistance to carbapenem entails a biological cost (less fitness) in all the experiments by pairs for the K. pneumoniae strain assayed.

•This biological cost hinders their competition with carbapenem-sensitive strains in the normal intestinal flora, which would make them less likely to cause infections.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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