RESUMO
BACKGROUND: The aim of this study was to characterize resistance of Escherichia coli in our environment to four associations of beta-lactams and beta-lactamase inhibitors (beta Lac) studying the influence of the type and level of beta Lac production. METHODS: The minimum inhibitory concentration (MIC) to ampicillin/sulbactam (A/S), amoxycillin/clavulanic acid (A/C), ticarcillin/clavulanic acid (T/C) and piperacillin/tazobactam (P/T) assessed was in 245 strains of E. coli resistant to ampicillin, consecutively isolated in our laboratory from September 1995 to March 1996. The beta Lac produced by these isolates were identified by isoelectrofocusing and spectrophotometrically quantified. RESULTS: The sensitivity to A/S, A/C, T/C and P/T was of 9.4, 86.9, 64.5 and 89.4%, respectively. The strains with only one beta Lac which cofocused with TEM-1 were the most frequent (215/245), followed by those producing a cofocusing enzyme with SHV-1 (7/245). A significant correlation was observed between beta Lact activity of the 215 TEM-1 strains and their MIC at A/S (r = 0.53; p < 0.001), A/C (r = 0.46; p < 0.001), T/TC (r = 0.58; p < 0.001), and P/T (r = 0.42; p < 0.001). The comparison between enzyme activity of the isolates of the different categories of susceptibility showed significant differences (p < 0.05) for the four associations studied. CONCLUSION: TEM-1 production is the main cause of resistance to beta-lactams in E. coli in our environment. The inhibitory efficacy of sulbactam, clavulanic acid and tazobactam over TEM-1 is inversely proportional to the amounts of enzyme produced. The high rate of resistance to A/S and T/C E. coli presents in our environment is mainly due to a hyperproduction of TEM-1.
