Detection of TEM beta-lactamase genes by non-isotopic spot hybridisation

A 998 bp fragment of plasmid pBR322, comprising part of the TEM-1 beta-lactamase gene, was labelled with biotin-11-dUTP for use as a DNA probe in a rapid non-isotopic spot hybridisation test. Diluted broth cultures of bacteria producing different beta-lactamases were filtered onto nitrocellulose and lysed in situ. Following pre-hybridisation treatment with proteinase K, hybridisation with the labelled probe was demonstrated using a commercially available streptavidine/polyalkaline phosphatase-based detection system. The probe was highly specific, reacting only with strains producing either the TEM-1 or structurally similar TEM-2 enzyme. An inoculum of 3-4 X 10(6) cells gave optimum positive discrimination. When 90 recent ampicillin-resistant strains of Escherichia coli isolated from patients with urinary tract infections were screened using the system, 72% gave a positive hybridisation signal.