Penicillinase in urine with high bacterial counts

Abstract

Penicillinase activity in 20 samples of urine exhibiting high bacterial counts was determined iodometrically. The enzymatic activity of 18 strains of Escherichia coli and two strains of Proteus mirabilis isolated from these samples was also determined by both the iodometric technique and a plate method. Positive results were found in 55% of the samples of urine. All the strains isolated from penicillinase-positive samples gave positive results when tested in pure cultures, whereas no penicillinase-producing strains were isolated from the samples giving negative results by the iodometric technique. Minimum inhibitory concentrations of benzylpenicillin were found to be extremely high in the strains recovered from positive samples (generally above 5000 μg/ml). The rest of the strains showed minimum inhibitory concentrations significantly lower (below 125 μg/ml). Penicillinase does not seem to exert its full activity in the urine, since quantitative results obtained with isolated strains were always higher. The hydrolysis of benzylpenicillin is inhibited when methicillin is added to the substrate.