Journal of Antimicrobial Chemotherapy (1996) 37, 931-942
© 1996 The British Society for Antimicrobial Chemotherapy
research-article |
In-vitro susceptibility of Klebsiella oxytoca strains to 13 ß-lactams in the presence and absence of ß-lactamase inhibitors
Laboratoire de Microbiologie, Höpital Saint-Louis (Université Paris VII) 75010 Paris, France
Received 27 July 1995; returned 12 October 1995; accepted 16 January 1996
*Correspondence to: B. Fournier, Laboratoire et service d'Infectiologie, Centre Hospitalier de L'Universite Laval, 2705 Boulevard Laurier, Sainte-Foy, Québec GIV4G2, Canada
The susceptibility of Klebsiella oxytoca isolates was tested by an agar diffusion method (167 strains collected in six countries) and an agar dilution method (38 strains). Multivariate analysis of inhibition zone diameters by principal component analysis clearly individualised four susceptibility patterns, including the phenotype of strains overproducing ß-lactamase and resistant to penicillins, first-generation cephalosporins, cefuroxime and aztreonam, but susceptible to ceftazidime. This phenotype was different from that conferred by plasmid-mediated extended-spectrum ß-lactamases; strains expressing these enzymes were also resistant to ceftazidime and cefotaxime. The blaoxy gene from K. oxytoca was introduced into Escherichia coli and K. oxytoca recipients and conferred increased resistance to ß-lactams in the recipient cells. Clavulanic acid was effective in association with piperacillin (MIC decreased 36-fold), ceftriaxone (35-fold) and aztreonam (19-fold) against overproducing strains, in spite of a relatively high IC50 (0.3 µm). Sulbactam (IC50, 400 µm) was ineffective in this context when combined with piperacillin (MIC decreased 1.5-fold), ceftriaxone (1.6-fold) and aztreonam (1.6-fold). The inhibitory activity of tazobactam (IC50, 8.2 µm) was heterogeneous depending on the strain and the ß-lactam with which it was combined. When combined with piperacillin or ceftriaxone little potentiation in antibiotic activity occurred (MIC decreased 3.9-fold and 4.5-fold, respectively); however, tazobactam plus aztreonam resulted in a 50-fold decrease in MIC of antibiotic.
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