DIRECT INOCULATION INTO MEDIA CONTAINING BILE-SALTS AND ANTIBIOTICS IS UNSUITABLE FOR THE DETECTION OF ACID SALT STRESSED ESCHERICHIA-COLI O157-H7/

The efficiency of selective enrichment broths for the recovery of low numbers of acid/salt stressed Escherichia roll 0157:H7 was determined. Stressed cultures were diluted to low levels and recovered in trypton e soya broth with added bile salts, to make modified tryptone soya bro th, and buffered peptone water with various combinations of antibiotic supplementation including novobiocin, acriflavine and a mixture of va ncomycin, cefsulodin and cefixime (VCC) at 37 degrees C and 42 degrees C. Significantly fewer stressed cells, in some cases as little as 0.3 % of the starting population, were recovered by all the selective enri chment broths containing bile salts or VCC antibiotics compared to the nonselective controls. The use of such enrichments to recover low num bers of stressed E. roll 0157:H7 may result in failure to detect the o rganism. Parallels with salmonella methodology are made and the need f or a non-selective pre-enrichment stage in E. coli 0157:H7 methods dis cussed.