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Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH PRODUCE

Location: Environmental Microbial & Food Safety Laboratory

Title: Evaluation of two immunomagnetic separation techniques for the detection and recovery of E. coli O157:H7 from finished composts

Author
item Reynnells, Russell
item Callahan, Mary Theresa
item Handy, Eric
item East, Cheryl - Roberts
item FELTON, GARY - University Of Maryland
item INGRAM, DAVID - Food And Drug Administration(FDA)
item Millner, Patricia
item Sharma, Manan

Submitted to: Journal of Food Analytical Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2014
Publication Date: 12/15/2014
Publication URL: http://handle.nal.usda.gov/10113/60251
Citation: Reynnells, R., Callahan, M.L., Handy, E.T., Roberts, C.L., Felton, G., Ingram, D., Millner, P.D., Sharma, M. 2014. Evaluation of two immunomagnetic separation techniques for the detection and recovery of E. coli O157:H7 from finished composts. Journal of Food Analytical Methods. doi: 10.1007/s12161-014-0068-4.

Interpretive Summary: Compost is organic matter (yardwaste, manure, biosolids, foodwaste) that has degraded into a nutrient-stable humus-like material that can be used as fertilizer for fruit and vegetable crops like lettuce and spinach. The composting process involves storing the feedstock in a manner to generate a thermophilic temperature (heat) to kill microbial pathogens and form the humus-like material. If this process is performed incorrectly, then there is the potential for bacterial pathogens like Escherichia coli O157:H7 to reside in the compost. These pathogens could potentially be transferred from the compost to a growing vegetable crop (like spinach or lettuce plants). Several produce-safety guidelines which growers follow state that the compost used in vegetable fields must be free of E. coli O157:H7; however, there are no specific or rapid microbial methods to test for the present of E. coli O157:H7. The research presented here shows that by using a technique called immunomagnetic separation (IMS) and combining it with direct plating (IMS/DP) or real-time polymerase chain reaction (IMS/PCR), low levels of the pathogen can be detected in compost. Both IMS/DP and IMS/PCR were able to detect E. coli O157:H7 in 100% (30/30) of the different inoculated compost samples tested. For IMS/PCR, removing inhibitors of the PCR (humic acid, polyphenols) before conducting the assay was extremely important to eliminate the potential for false-negative results. This information will be useful to other scientists and regulatory agencies.

Technical Abstract: Two rapid immunomagnetic separation (IMS) protocols were evaluated to recover 1-2 log CFU/g inoculated E. coli O157:H7 from 30 different commercial, finished compost samples. Both protocols detected E. coli O157:H7 in compost samples; PCR techniques required the removal of inhibitors to reduce possibility of a false negative result.