Comparison of enrichment media for recovery of Escherichia coli O157:H7 from meat and environmental samples

Authors: Johnson, Sarah; Luchansky, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2008
Publication Date: 8/3/2008
Citation: Johnson, S., Luchansky, J.B. 2008. Comparison of enrichment media for recovery of Escherichia coli O157:H7 from meat and environmental samples. Meeting Abstract. P3-12. Page 105.

Interpretive Summary:

Technical Abstract: Introduction: Sensitive and reliable enrichment methods are needed for detection of E. coli O157:H7 in foods. Purpose: Evaluate media for recovery of E. coli O157:H7 from meat and environmental samples in response to a USDA/FSIS need to decrease enrichment time from 20-24 to 15 hours. Methods: E. coli O157:H7 ATCC 43888 was used to evaluate the performance of modified E. coli broth containing novobiocin (mEC+n) incubated at 35 degree C and 42 degree C, with RapidChek E. coli O157:H7 broth at 42 degree C, BioControl mEHEC broth at 42 degree C, Dupont BAX E. coli O157:H7 broth at 42 degree C, and modified tryptone soya broth (mTSB) both with and without novobiocin at 42 degree C. The mTSB+n @ 42 degree C was further compared to mEC+n at 35 degree C using ground beef, summer sausage, hard salami, cooked beef patties, beef trim, and environmental samples spiked with E. coli O157:H7 at 4 or 20 CFU/25g and then incubated for 15 hours. Results: There was no statistical difference (P<0.05) between mTSB+n and the commercial media using the Bactometer, BAX PCR assay, or standard plate counts (CFU/ml) on BHI agar. These same media had shorter Bactometer detection times and higher percentages of BAX positive test results than mEC+n at 35 degree C or 42 degree C. Also, more CFU/ml were recovered from mTSB+n and the commercial media after 15 hours at 42 degree C than from mEC+n at 35 degree C and 42 degree C. Additionally, more samples tested positive using the BAX PCR assay for summer sausage, hard salami, and beef trim following enrichment in mTSB+n at 42 degree C than from mEC+n at 35 degree C. However, no difference in performance was seen with cooked beef patties or environmental samples between these two media using the BAX PCR assay. Significance: Enrichment of contaminated meat samples in mTSB+n for 15 hours at 42 degree C is a suitable method for recovery of E. coli O157:H7.