Use of a non-radioactive hybridisation assay for direct detection of gram-negative bacteria carrying TEM β-lactamase genes in infected urine

DNA in infected urines from 81 patients with urinary tract infection was hybridised directly with a non-radioactive DNA probe specific for bacterial genes coding for TEM-type β-lactamase. The results were assessed by means of a computerised image analysis system and compared with those obtained following isolation of the infecting organism, conventional sensitivity testing and isoelectric focusing (IEF) procedures for the detection of TEM-type β-lactamase. Of the 27 ampicillin-resistant gram-negative organisms isolated in pure culture from the urines, 14 were shown by both hybridisation and IEF to carry a gene for TEM β-lactamase production. Only four discordant results were obtained: three 'false positive' direct hybridisation results, one due to urine pigmentation, and one, possibly, to a TEM β-lactamase gene which was not being expressed, and one 'false negative' result due to insufficient cell numbers in the urine. The system is capable of screening large numbers of samples and is applicable to any gene for which a suitable DNA probe is available.