1984 Volume 75 Issue 4 Pages 600-610
A total of 355 strains isolated from urine specimens of 196 patients with complicated urinary tract infections were studied for β-lactamase production. β-Lactamase activity was qualitatively determined by a paper strip acidimetric method with benzylpenicillin as substrate and by a chromogenic cephalosporin method with nitrocefin as substrate. The β-lactamase-producing strains which could be detected by at least one of the two methods were found in 44 out of 77 (57.1%) Escherichia coli isolates, 12 out of 59 (20.3%) Pseudomonas aeruginosa isolates, 47 out of 51 (92.2%) Serratia marcescens isolates, 26 out of 32 (81.3%) Klebsiella spp. isolates, 17 out of 17 (100%) Citrobacter freundii isolates, 14 out of 54 (25.9%) of the other gram-negative rods and 1 of 63 (1.5%) of gram-positive cocci. Of 79 β-lactamase-producing strains of the gram-negative rods which could be detected by the chromogenic cephalosporin method, the enzymic activities of 63 strains were inhibited by clavulanic acid, those of 5 strains by cefmetazole and those of 11 strains by the two drugs, in vitro. From these results, the high detection rate of β-lactamases, especially the penicillinases produced by gram-negative rods, might be a clinical problem in the treatment of complicated urinary tract infections.
