AN ALANINE RACEMASE GENE AS A NEW INDEX FOR DETECTING ESCHERICHIA-COLI IN FOODS

A gene of alanine racemase, a typical prokaryotic enzyme, was evaluate d as a new index for detecting Escherichia coli in foods, An alanine r acemase gene fragment containing a non-conserved sequence of the gene was amplified from genomic DNA of E. coli by a polymerase chain reacti on, and then labeled with digoxigenin as a probe for detecting E. coli . Food samples and bacteria were each treated as at 25 degrees C for 1 0 min in 0.1 N NaOH containing 0.5% SDS, before being directly spotted on to nylon membranes for DNA hybridization. The probe was specific f or E. coli; all 48 strains of E. coli examined, including such pathoge nic strains as E. coli O157:H7, showed positive signals, whereas all 5 9 strains of non-E. coli species, except for one strain (Shigella sonn ei), did not show a signal. Various foods inoculated with E. coli K-12 showed positive signals, whereas no uninoculated foods showed any sig nal. Quantification of E. coli cells in the death phase by the hybridi zation method showed good correlation with that by the plate culture m ethod. The alanine racemase gene could prove useful as an index for de tecting E. coli in foods.