Rapid detection of a specific trimethoprim resistance gene using a biotinylated DNA probe.

A DNA probe specific for the dihydrofolate reductase (DHFR) type I gene was labelled with biotin by the process of nick-translation and used to screen 83 independently-derived trimethoprim R plasmids from Enterobacteriaceae. Hybridization was detected using streptavidine and a biotin-conjugated alkaline phosphatase to generate an insoluble coloured precipitate following the addition of an appropriate dye. Sixty-eight plasmids (81.9%) hybridized with the probe for DHFR type I. The method could be adapted for use with any antibiotic resistance gene for which a suitable DNA probe is available and has none of the drawbacks associated with the use of radioactively-labelled DNA in hybridization techniques.