In vitro activities of antibacterial agents against clinical isolates of Escherichia coli and Klebsiella species from intensive care units.

The susceptibility of 293 cultures of Escherichia coli and 160 cultures of Klebsiella species isolated consecutively from patients in intensive care units at 25 New York area hospitals to four antibiotic agents was determined. Susceptibility testing was performed with the reference agar dilution and broth microdilution procedures. At the minimum inhibitory concentration (MIC) breakpoints (specified in the prescribing information) of less than or equal to 4 micrograms/ml for imipenem, less than or equal to 16 micrograms/ml for cefoxitin, less than or equal to 8 micrograms/ml for ampicillin/sulbactam, and less than or equal to 64 micrograms/ml for ticarcillin/clavulanic acid, all isolates tested were susceptible to imipenem, 98% each of E coli and Klebsiella isolates were susceptible to cefoxitin, 75% and 83% to ampicillin/sulbactam and 96% and 92% to ticarcillin/clavulanic acid. At the recommended National Committee for Clinical Laboratory Standards MIC breakpoints (less than or equal to 4 micrograms/ml for imipenem, less than or equal to 8 micrograms/ml for cefoxitin, less than or equal to 8/4 micrograms/ml for ampicillin/sulbactam, and less than or equal to 16/2 micrograms/ml for ticarcillin/clavulanic acid) all isolates were susceptible to imipenem, 97% of E coli and 98% of Klebsiella isolates were susceptible to cefoxitin, 75% and 83% to ampicillin/sulbactam, and 86% each to ticarcillin/clavulanic acid. Of the 122 isolates with MICs greater than or equal to 128 micrograms/ml to ampicillin, only 19% were susceptible to ampicillin/sulbactam; and of the 150 isolates with MICs greater than 128 micrograms/ml to ticarcillin, 61% were susceptible to ticarcillin/clavulanic acid. The results suggest that, in the antibiotic combinations studied, high levels of penicillinases, capable of significantly affecting the utility of the enzyme inhibitors, are produced.