Comparison of enrichment procedures for isolation of Escherichia coli O157: H7 front ground beef and radish sprouts

Enrichment procedures usings Tryptic soy broth (TSB), modified TSB (mTSB), modified E. coli broth with novobiocin (mEC + n), mTSB (without novobiocin) with vancomycin, cefixime and cefsulodin (mTSB-VCC), or TSB with cefixime, tellurite and vancomycin (TSB-CTV) were evaluated by determining the rate of successful isolation of fifteen Escherichia coli O157.H7 strains from in oculated broth containing ground beef or radish sprout extract. E. coli O15 7:H7 tended to be isolated more efficiently after enrichment with TSB, mTSB and mEC + n than with the other broths. In order to identify the most effi cient enrichmemt condition using these broths, E. coli O157:H7 were inocula ted into 25 g ground beef or radish sprouts, which were then homogenized in 225 ml broth and incubated static at 37 degrees C or 42 degrees C for 6 h or 18 h. Attempts were made to isolate the inoculated bacteria by plating m ethod in combination with the immunomagnetic separation method. The most ef fective enrichment condition was incubation in mTSB or mEC + n at 42 degree s C for 18 h for ground beef, and in mEC + n at 42 degrees C for 18 h for r adish sprouts. (C) 1999 Elsevier Science B.V. All rights reserved.