Occurrence of Coliform and Escherichia coli Contamination and Absence of Escherichia coli O157:H7 on Romaine Lettuce from Retail Stores in the Upper Midwest

Journal of Food Protection
Josephine D GreveJay L E Ellingson

Abstract

A total of 720 whole, romaine lettuce heads were purchased from retail locations in the Upper Midwest and assessed for coliform and Escherichia coli contamination and for the presence of E. coli O157:H7. During a 16-month period (August 2010 through December 2011), coliform and E. coli counts were enumerated on Petrifilm, and the presence of E. coli O157:H7 and the virulence gene eae was evaluated by real-time PCR (qPCR). Over half (400 of 720) of the lettuce samples were processed with an immunomagnetic separation step before the qPCR assay. All retail lettuce samples were negative for E. coli O157:H7 when tested with the R.A.P.I.D. LT qPCR targeting a region of the O-antigen, and only two (0.28%) were positive for the eae gene when tested with LightCycler qPCR. On Petrifilm, coliform counts of most lettuce samples (96.4%) were between <10(1) and 10(3) CFU/g, and E. coli counts for nearly all lettuce samples (98.2%) were <10(1) CFU/g. No seasonal trend in coliform and E. coli counts was observed throughout the examination period nor was a difference in coliform counts observed between packaged and nonpackaged lettuce heads. These results contribute to the limited recorded data and understanding of microbial contamination of wh...Continue Reading

References

Mar 24, 1983·The New England Journal of Medicine·L W RileyM L Cohen
Mar 31, 2005·Molecular and Cellular Probes·Jay L E EllingsonVijay K Sharma
Aug 24, 2006·Journal of Food Protection·Avik MukherjeeFrancisco Diez-Gonzalez
Oct 19, 2006·International Journal of Food Microbiology·Lynette M JohnstonChristine L Moe
Dec 2, 2010·Foodborne Pathogens and Disease·Witold A Ferens, Carolyn J Hovde
Jan 10, 2012·Journal of Food Protection·Julie A KasePeter C H Feng
May 22, 2013·Proceedings of the National Academy of Sciences of the United States of America·Steven D ZumbrunAlison D O'Brien

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