Formation and Control of the Viable but Non-culturable State of Foodborne Pathogen O157:H7.

As a common foodborne pathogen, O157:H7 produces toxins causing serious diseases. However, traditional methods failed in detecting O157:H7 cells in the viable but non-culturable (VBNC) state, which poses a threat to food safety. This study aimed at investigating the formation, control, and detection of the VBNC state of O157:H7. Three factors including medium, salt, and acid concentrations were selected as a single variation. Orthogonal experiments were designed with three factors and four levels, and 16 experimental schemes were used. The formation of the VBNC state was examined by agar plate counting and LIVE/DEAD BacLight bacterial viability kit with fluorescence microscopy. According to the effects of environmental conditions on the formation of the VBNC state of O157:H7, the inhibition on VBNC state formation was investigated. In addition, in the VBNC state in food samples (crystal cake) was detected by propidium monoazide-polymerase chain reaction (PMA-PCR) assays. Acetic acid concentration showed the most impact on VBNC formation of O157:H7, followed by medium and salt concentration. The addition of 1.0% acetic acid could directly kill O157:H7 and eliminate its VBNC formation. In crystal cake, 25, 50, or 100% medium with 1.0% acetic acid could inhibit VBNC state formation and kill O157:H7 within 3 days. The VBNC cell number was reduced by adding 1.0% acetic acid. PMA-PCR assay could be used to detect VBNC cells in crystal cake with detection limit at 10 CFU/ml. The understanding on the inducing and inhibitory conditions for the VBNC state of O157:H7 in a typical food system, as well as the development of an efficient VBNC cell detection method might aid in the control of VBNC O157:H7 cells in the food industry.