Sensitivity to carbenicillin and ticarcillin, and the beta-lactamases of Pseudomonas aeruginosa in the UK in 1978-79.

Abstract

A total of 438 strains of P. aeruginosa supplied by 10 hospitals in the UK reporting an increase in resistance to carbenicillin was tested for sensitivity to carbenicillin and ticarcillin. It was found that 85% of the strains were inhibited by 125 .mu.g carbenicillin/ml and 87% by 50 .mu.g ticarcillin/ml, and that ticarcillin was from 2- to 4-fold more active than carbenicillin against the majority of these strains. Strains with a high level of resistance to carbenicillin (MIC [minimal inhibitory concentration] > 1000 .mu.g/ml) possessed constitutive .beta.-lactamases and 5 different types of enzyme were identified. There was good correlation between MIC and the results of disc sensitivity tests in this study, 82% with the 100 .mu.g carbenicillin disc and 90% with the 75 .mu.g ticarcillin disc, but results reported in the hospital laboratory tests with the carbenicillin disc were less satisfactory (64% correlation). From a comaprison with data reported in 1967 there does not appear to have been a significant increase in the incidence of carbenicillin-resistant strains of P. aeruginosa in the UK.