Study of the in vitro activity of amoxicillin/clavulanic acid and other beta-lactam antibiotics against Escherichia coli isolated from urine specimens

A total of 205 serial, unduplicated urinary isolates of Escherichia coli wa s collected from June through August 1998 in 2 community and 3 hospital lab oratories. By using the NCCLS broth microdilution technique, their in vitro susceptibility to ampicillin, amoxicillin/clavulanic acid, cefuroxime, cef uroxime axetil, ticarcillin/clavulanic acid and piperacillin/tazobactam was determined. One hundred and twenty isolates were from hospitalised patient s, 85 from ambulatory, 129 community acquired and 76 nosocomial. Half of th e nosocomial isolates were obtained from naturally produced and half from a lternatively produced urine specimens. In general, the highest susceptibili ty rates, following NCCLS criteria, were found for piperacillin/ tazobactam (93.2%) followed by cefuroxime (92.2%) and amoxicillin/clavulanic acid (82 .9%). Ampicillin showed a clear bimodal distribution with a clear peak fur the resistant population. The highest degree of ampicillin resistance was f ound in nosocomial isolates. Overall, ampicillin showed the lowest degree o f susceptibility. Most of the ampicillin resistant isolates remained suscep tible to piperacillin/tazobactam, cefuroxime and amoxicillin/clavulanic aci d. In general, the community acquired isolates had higher susceptibility ra tes than the nosocomial isolates.