[Clinical significance of bacterial beta-lactamase production in the treatment of urinary tract infections with oral beta-lactam-antibiotics].

In 649 urological patients with urinary tract infections (UTI) a total of 1114 bacterial strains were isolated and their beta-lactamase production was investigated by a qualitative, micro-iodometric method. Approximately 40% of all strains, 33% of E. coli species and 8% of Proteus mirabilis species were enzyme producers. All of the isolates of E. coli and Proteus mirabilis defined as non-producers were sensitive to ampicillin and cephalothin in the agar diffusion test. The beta-lactamase producers of these two species did not show the same pattern: almost all of them were ampicillin-resistant, but most were cephalothin-sensitive. The other species were all found to be either producers or non-producers. Therapeutic comparisons in altogether 138 UTI patients treated with ampicillin or cephalexin, two antibiotics with different beta-lactamase stability, confirmed the positive correlation between enzyme production and therapeutic failure in both groups. Cephalexin, however, tended to be more effective than ampicillin against enzyme-producing species.