Plasmid-mediated beta-lactam resistance in pathogenic gram-negative bacteria isolated in south India

A field study was undertaken at the Christian Medical College Hospital in Vellore, South India in 1984. Two hundred and eighty-four clinical isolates of enterobacteria were collected from patients with significant bacteriuria and their sensitivities to a series of beta-lactam antibiotics were determined. There was a very high incidence of beta-lactam resistance (ampicillin resistance greater than 80% and cephaloridine resistance greater than 65%) amongst these isolates. There was significant resistance to the combination of ampicillin and clavulanic acid but few of the isolates were resistant to cefuroxime or ceftazidime. Seventy seven per cent of the Escherichia coli isolates were resistant to ampicillin and 57% were resistant to cephaloridine. Most of the resistant Esch. coli isolates carried resistance genes for both ampicillin and cephaloridine which were transferable, either by direct conjugation or by mobilization with the X+ plasmid. Characterization of the R-plasmids revealed considerable diversity. Although the distribution of plasmid-mediated beta-lactamases was broadly similar to those found in other surveys, three new beta-lactamases were identified and atypically some of the Esch. coli isolates produced PSE beta-lactamases.