Prevalence of Ticarcillin/Clavulanic Acid-Resistant Enterobacteriacaeae in Nine Separate Medical Centers During the Years 1983, 1989, and 1991

Abstract

The combination of ticarcillin with clavulanic acid has proven to be an effective antimicrobial agent. For in vitro susceptibility testing doubling dilutions of ticarcillin are combined with a fixed concentration of 2 µg clavulanic acid per ml.^5,6 Resistance to ticarcillin/clavulanic acid (T/C) has been relatively uncommon among the Enterobacteriaceae.^2,5,6,9 In 1988, Sanders et al. described strains of Escherichia coli and Klebsiella pneumoniae that were T/C resistant because they produced excess amounts of β-lactamase enzymes which could not be completely neutralized by the low concentration of clavulanic acid (2 µg/ml) that is normally tested in vitro.¹¹ Whether strains with elevated T/C MICs should be considered clinically resistant is a matter of presumption. The inability of the disk diffusion test to detect such hyper-producers of β-lactamase enzymes has been studied, but the clinical relevance of those discrepant results has yet to be evaluated.^3,7,11