Evaluation of Two Immunomagnetic Separation Techniques for the Detection and Recovery of Escherichia coli O157:H7 from Finished Composts

What is it about?

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.

Featured Image