Food Protection Trends - July 2008 - 472

and Shigella dysenteriae (6). With the exception of S. dysenteriae, all bacteria produced negative test results. The inclusion of the phage-only control (the control in which an un-inoculated piece of meat was tested) allowed evaluation of the ability of the test to work in a meat sample in the presence of natural background flora. Specifically, we were interested in assessing the possibility of false positive results due to the presence of native bacteria on the meat. The results indicated that in both the colorimetric and the luminescent tests, the phage-only control remained negative (Fig. 3, C2; in the luminescent test, the background RLU were subtracted from each test). Therefore, the presence of background flora on the meat surface is unlikely to interfere with the ability of the Phast Swab to detect the presence of E. coli O157:H7. In its current stage of development, the Phast Swab is estimated to cost approximately $4.74 per test for the colorimetric version and $5.34 per test for the luminescent version. These costs compare extremely favorably to other commercially available E. coli O157:H7 rapid tests, although only reagent costs were taken into consideration in determining the cost per test of the Phast Swab, and other manufacturing costs, such as labor, would increase the cost of production. Reporter bacteriophages have been used to detect several foodborne pathogens, including Salmonella spp. (2), and Listeria monocytogenes (8). Recently Oda et al. (11) have used a GFP labeled bacteriophage to detect E. coli O157:H7. The method is simple and rapid, but requires the use of a fluorescent microscope to view the test result. In this study, we show that a β-galactosidase reporter phage can be combined into an integrated assay to detect viable E. coli O157:H7 efficiently and rapidly on beef samples. The Phast Swab is a novel, simple assay that can be utilized to detect the presence of low levels of E. coli O157:H7 within 10 to 12 hours. The colorimetric Phast Swab assay is easy to perform, results are available within 12 hours, and the use of a colorimetric substrate in the assay also eliminates the need for instrumentation to read the test result. The luminescent Phast Swab delivers test results in 10 hours and is easily read in a handheld luminometer. These portable luminometers are already widely used in the food industry to monitor hygiene by the ATP assay, which increases the likelihood that the luminescent Phast Swab could become widely accepted. It is conceivable that the Phast Swab assay could be used to test beef carcasses, beef trim, and contact surfaces for the presence of E. coli O157:H7, as part of a carcass monitoring program for this pathogen. ACKNOWLEDGMENTS This research was supported by a USDA National Research Initiative grant (2005-01879), a Wyoming National Aeronautical and Space Agency Consortium Space Grant, and a Colorado Space Grant. The authors thank Dr. Neil Percy at Hygiena Corporation for supplying the Snap Valve ™ devices, and Shane Thompson in the University of Wyoming Meat Laboratory for supplying the meat samples. REFERENCES 1. Center for Infectious Disease and Policy. 2007. Six-state E. coli outbreak blamed on ground beef. Available at http://www.cidrap.umn. edu/cidrap/content/fs/food-disease/ news/jun1107ecoli.html. Accessed on 11/12/07. 2. Chen, J., and M. W. Griffiths. 1996. Salmonella detection in eggs using lux+ bacteriophages. J. Food Prot. 59:908–914. 3. Food Safety Inspection Service. 2007. FSIS recalls: open federal cases. Available at http://www.fsis. usda.gov/Fsis_Recalls/Open_Federal_Cases/index.asp. Accessed on 11/12/07. 4. Gilligan, P. H. 1999. Escherichia coli. EAEC, EHEC, EIEC, ETEC. Clin. Lab. Med. 19:505–521. 5. Goodridge, L., and M. W. Griffiths. 2002. Reporter bacteriophage assays as a means to detect foodborne pathogenic bacteria. Food Res. Intern. 35:863–870. 6. Goodridge, L. D., and J. Willford. 2006. Development of the Phast Swab for rapid detection of enterohemorrhagic Escherichia coli. 1st Texas/Evergreen Phage/Virus Genomics and Ecology Meeting, Kingsville, Texas. 7. Lejeune, J. T., and M. D. Kauffman. 2005. Effect of sand and sawdust bedding materials on the fecal prevalence of Escherichia coli O157:H7 in dairy cows. Appl Environ Microbiol. 71:326–330. 8. Loessner, M J., M. Rudolf, and S. Scherer. 1997. Evaluation of luciferase reporter bacteriophage A511::luxAB for detection of Listeria monocytogenes in contaminated foods. Appl. Environ. Microbiol. 63:2961–2965. 9. Mead, P. S., L. Slutsker, V. Dietz, L . F. M c C a i g , J . S . B r e s e e , C. Shapiro, P. M. Griffin, and R. V. Tauxe. 1999. Food-related illness and death in the United States. Emerg. Infect. Dis. 5:607–625. 10. Nataro, J. P., and J. B. Kaper. 1998. Diarrheagenic Escherichia coli. Clin Microbiol. Rev. 11:142–201. 11. Oda, M, M. Morita, H. Unno, and Y. Tanji. 2004. Rapid detection of Escherichia coli O157:H7 by using green fluorescent protein-labeled PP01 bacteriophage. Appl. Environ. Microbiol. 70:527–534. 12. Schenborn, E., and D. Groskreutz. 1999. Reporter gene vectors and assays. Mol. Biotechnol. 13:29–44. 472 FOOD PROTECTION TRENDS | JULY 2008

http://www.fsis.usda.gov/Fsis_Recalls/Open_Federal_Cases/index.asp http://www.fsis.usda.gov/Fsis_Recalls/Open_Federal_Cases/index.asp http://www.fsis.usda.gov/Fsis_Recalls/Open_Federal_Cases/index.asp http://www.cidrap.umn.edu/cidrap/content/fs/food-disease/news/jun1107ecoli.html http://www.cidrap.umn.edu/cidrap/content/fs/food-disease/news/jun1107ecoli.html http://www.cidrap.umn.edu/cidrap/content/fs/food-disease/news/jun1107ecoli.html

Food Protection Trends - July 2008

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