Principal beta-lactamases responsible for resistance to beta-lactam antibiotics in urinary tract infections

Abstract

Two independent surveys were conducted to determine the prevalent bacterial species and .beta.-lactamase types present in clinical populations of gram-negative, ampicillin-resistant isolates. A total of 208 isolates (112 from Nottingham Hospital and 96 from Charing Cross Hospital), all of which were collected from out-patients suffering from urinary tract infections, were investigated. The incidence of ampicillin-resistant isolates (minimum inhibitory concentration, 8 .mu.g/ml) was 24.1 and 18.8% within the Nottingham and Charing Cross samples, respectively. The surveys gave similar results within the ampicillin-resistant samples. Escherichia coli was the prevalent bacterial species (52.9%), followed by Klebsiella pneumoniae (30.3%). The majority of isolates, at least 54.8% and possibly as high as 74.5%, owed their principal .beta.-lactamase activity to enzymes mediated by R-plasmids. The most prevalent .beta.-lactamases were TEM-1 (53.3%), SHV-1 (30.9%), and OXA-1 (11.5%). Positive associations were found between E. coli and TEM-1 or OXA-1 and between K. pneumoniae and SHV-1.