Simultaneous Enrichment of Shiga Toxin

Simultaneous enrichment of shiga toxin-producing Escherichia coli O157 and O26 and Salmonella in food samples using universal preenrichment broth.

J Food Prot. 2009 Oct;72(10):2065-70.

Kanki M,Seto K, Sakata J, Harada T, Kumeda Y.

Division of Bacteriology, Osaka Prefectural Institute of Public Health, 1-3-69 Nakamichi, Higashinari-ku, Osaka 537-0025, Japan.

Abstract

Universal preenrichment broth (UPB) was compared with modified Escherichia coli broth with novobiocin (mEC+n) for enrichment of Shiga toxin-producing E. coli O157 and O26, and with buffered peptone water (BPW) for preenrichment of Salmonella enterica. Ten strains each of the three pathogens were inoculated into beef and radish sprouts following thermal, freezing, or no treatment. With regard to O157 and O26, UPB incubated at 42 degrees C recovered significantly more cells from inoculated beef than UPB at 35 degrees C and from radish sprout samples than UPB at 35 degrees C and mEC+n. With regard to Salmonella, UPB incubated at 42 degrees C was as effective as UPB at 35 degrees C and BPW at recovering cells from beef and radish sprout samples. No significant difference was noted between the effectiveness of UPB at 42 degrees C and UPB at 35 degrees C or BPW in the recovery of Salmonella from 205 naturally contaminated poultry samples. By using UPB at 42 degrees C, one O157:H7 strain was isolated from the mixed offal of 53 beef samples, 6 cattle offal samples, and 50 pork samples all contaminated naturally, with no pathogen inoculation. The present study found that UPB incubated at 42 degrees C was as effective as, or better than, mEC+n for enrichment of O157 and O26 and comparable to BPW for preenrichment of Salmonella. These findings suggest that a great deal of labor, time, samples, and space may be saved if O157, O26, and Salmonella are enriched simultaneously with UPB at 42 degrees C.