This study evaluated whether E. coli O157:H7 exists in a viable but non-culturable (VNC) state when in contact with beef products and to evaluate those factors which cause the pathogen to enter this state. The VNC state exists when an organism encounters “challenging” external factors, such as sanitizers, temperature changes or a shift in nutrients. This is important because in this state, the organism may not be detected but may still cause illness should it be ingested.
Varying combinations of pH, chloride concentration and temperature ranges were used to evaluate the conditions that would place E. coli O157:H7 in a VNC state. The results indicate that the pathogen did not reach the VNC state within 14 days of sampling under the various conditions. Also, VNC pathogens that were introduced into raw ground beef did not resuscitate into culturable organisms within the given timeframe.
Results of this study suggest that E. coli O157:H7 do not rapidly enter the VNC state following exposure to adverse conditions and that pathogens in the VNC state remain viable for extended periods in raw hamburger. However, this study did demonstrate that E. coli O157:H7 will enter the VNC state after prolonged incubation in nutrient limiting media. In turn, bacteria may reside on equipment improperly cleaned and sanitized and ultimately enter the VNC state. Future studies are needed to determine the fate of VNC state cells in the host.