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Antimicrobial Agents and Chemotherapy, March 1999, p. 476-482, Vol. 43, No. 3
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Two-Step Acquisition of Resistance to the Teicoplanin-Gentamicin Combination by VanB-Type Enterococcus faecalis In Vitro and in Experimental Endocarditis

Agnès Lefort,1 Marina Baptista,2 Bruno Fantin,1,* Florence Depardieu,2 Michel Arthur,2 Claude Carbon,1 and Patrice Courvalin2

Institut National de la Santé et de la Recherche Médicale, Hôpital Bichat-Claude Bernard,1 and Unité des Agents Antibactériens, Institut Pasteur,2 Paris, France

Received 11 September 1998/Returned for modification 23 October 1998/Accepted 30 December 1998

The activity of vancomycin and teicoplanin combined with gentamicin was investigated in vitro against strains of Enterococcus faecalis resistant to vancomycin and susceptible to teicoplanin (VanB type) and against mutants that had acquired resistance to teicoplanin by three different mechanisms. In vitro, gentamicin selected mutants with two- to sixfold increases in the level of resistance to this antibiotic at frequencies of 10-6 to 10-7. Teicoplanin selected teicoplanin-resistant mutants at similar frequencies. Both mutations were required to abolish the activity of the gentamicin-teicoplanin combination. As expected, simultaneous acquisition of the two types of mutations was not observed. In therapy with gentamicin or teicoplanin alone, each selected mutants in three of seven rabbits with aortic endocarditis due to VanB-type E. faecalis BM4275. The vancomycin-gentamicin combination selected mutants that were resistant to gentamicin and to the combination. In contrast, the teicoplanin-gentamicin regimen prevented the emergence of mutants resistant to one or both components of the combination. These results suggest that two mutations are also required to suppress the in vivo activity of the teicoplanin-gentamicin combination.

* Corresponding author. Present address: Unité de Médecine Interne, Hôpital Beaujon, 100 boulevard du Général Leclerc, 92118 Clichy Cedex, France. Phone: (33) (1) 40 87 58 90. Fax: (33) (1) 40 87 54 95. E-mail: bruno.fantin{at}bjn.ap-hop-paris.fr.

Antimicrobial Agents and Chemotherapy, March 1999, p. 476-482, Vol. 43, No. 3
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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