Detection of culturable Salmonella and its formation of a viable but non-culturable state under oxidative stresses

Abstract:

[Background] Bacteria would enter a viable but non-culturable (VBNC) state under oxidative stress, and their colony forming ability may be affected by sublethal injury that imposed on bacterial cells. Currently, the quantitative detection of VBNC bacteria is based on the difference between the viable and culturable counts. Therefore, the accurate detection of culturable counts is critical to quantitating the number of VBNC cells. In addition, a proper growth medium might avoid the missing detection of viable pathogenic bacteria. [Objective] To analyze the effect of medium composition on the detection of bacteria exposed to sublethal injury caused by oxidative stresses, and to explore the formation of VBNC state of Salmonella enterica serovar Enteritidis under oxidative stresses. [Methods] The culturable cells in Luria-Bertani (LB), beef peptone yeast (BPY), and Salmonella Shigella (SS) medium were counted and compared. The formation of VBNC S. enterica serovar Enteritidis was quantified respectively with RT-qPCR and fluorescent staining under confocal laser microscope. [Results] The sublethal injured cells under oxidative stress could be detected with non-selective LB and BPY medium, and the counts of culturable cells reduced in SS medium because of bile salt. The formation rate of VBNC S. enterica serovar Enteritidis exposed to H₂O₂at 53 °C for 1.5 h was significantly higher than that in the other two cases (P<0.05). [Conclusion] For the detection of VBNC state, a suitable medium should be selected to detect culturable cells. Oxidative stress would induce the VBNC state of food-borne pathogens, which deserves special attention as H₂O₂ is widely used as a disinfectant in food processing and medical treatment.

Key words:Salmonella enterica serovar Enteritidis;oxidative stress;viable but non-culturable state;culture medium optimization