Comparison of Enrichment Procedures for Isolation of Escherichia Coli O157 From Ground Beef and Radish Sprouts

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

1999; Int J Food Microbiol.

50:211-214. Hara-Kudo Y(a), Onoue Y(b), Konuma H(c), Nakagawa H(d), Kumagai S.(a)

^a Department of Biomedical Food Research, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162, Japan
^b Kanagawa Prefectural Public Health Laboratory, 52-2 Nakao-cho, Asahi-ku, Yokohama 241, Japan
^c Division of Microbiology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158, Japan
^d Tokyo Kenbikyoin Foundation, 44-1 Nihonbashi Hakozaki-cho, Chuo-ku, Tokyo 103, Japan

Abstract

Enrichment procedures using 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 inoculated broth containing ground beef or radish sprout extract. E. coli O157: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 efficient enrichmemt condition using these broths, E. coli O157:H7 were inoculated into 25 g ground beef or radish sprouts, which were then homogenized in 225 ml broth and incubated static at 37°C or 42°C for 6 h or 18 h. Attempts were made to isolate the inoculated bacteria by plating method in combination with the immunomagnetic separation method. The most effective enrichment condition was incubation in mTSB or mEC+n at 42°C for 18 h for ground beef, and in mEC+n at 42°C for 18 h for radish sprouts.