Prophage induction reduces Shiga toxin producing Escherichia coli (STEC) and Salmonella enterica on tomatoes and spinach: A model study

Abstract

Fresh produce is increasingly implicated in foodborne outbreaks and most fresh produce is consumed raw, emphasizing the need to develop non-thermal methods to control foodborne pathogens. This study investigates bacterial cell lysis through induction of prophages as a novel approach to control foodborne bacterial pathogens on fresh produce. Shiga toxin producing Escherichia coli (STEC) and Salmonella enterica isolates were exposed to different prophage inducers (i.e. mitomycin C or streptonigrin) and growth of the cells was monitored by measuring the optical density (OD 600) during incubation at 37 C. Beginning at three hours after addition of the inducer, all concentrations (0.5, 1, 2 mg/mL) of mitomycin C, or 2 mg/mL streptonigrin significantly reduced the OD 600 in broth cultures, in a concentration dependent manner, relative to cultures where no inducer was added. PCR confirmed bacterial release of induced bacteriophages and demonstrated that a single compound could successfully induce multiple types of prophages. The ability of mitomycin C to induce prophages in STEC O157:H7 and in S. enterica (serovars Typhimurium and Newport) on fresh produce was evaluated by inoculating red greenhouse tomatoes or spinach leaves with 5 Â 10 7 and 5 Â 10 8 colony forming units, respectively. After allowing time for the inoculum to dry on the fresh produce samples, 6 mg/mL mitomycin C was sprayed onto each sample, while control samples were sprayed with water. Following overnight incubation at 4 C, the bacterial cells were recovered and plate counts were performed. A 3 log reduction in STEC O157:H7 cells was observed on tomatoes sprayed with mitomycin C compared to those sprayed with water, while a 1 log reduction was obtained on spinach. Similarly, spraying mitomycin C on tomatoes and spinach inoculated with S. enterica isolates resulted in a 1-1.5 log and 2 log reduction, respectively. These findings serve as a proof of concept that prophage induction can effectively control bacterial foodborne pathogens on fresh produce.

Xenobiotic Effects of Chlorine Dioxide to Escherichia coli O157:H7 on Non-host Tomato Environment Revealed by Transcriptional Network Modeling: Implications to Adaptation and Selection

“…Because E. coli O157:H7 is one of the most dangerous serotypes threatening public health (Watanabe et al, 1996;Yang et al, 2017), different strategies such as on-farm hygiene, washing, film coating, prophage induction, and use of interventions through sodium hypochlorite (NaClO), sodium chlorite (NaClO 2 ), acidified sodium benzoate (NaB), and peracetic acid (PAA) have been applied to control the bacterial population retained on the surface of fresh tomato (Cadieux et al, 2018;Chen and Zhong, 2018;Singh et al, 2018). However, effective, safe, and sustainable treatment strategies that reduce fruit contamination have been difficult to achieve possibly due in large part to the poor understanding of the molecular and genetic mechanisms involved in the responses of E. coli to chemical treatments.…”

Application of Bacteriophages in Nanotechnology

“…It was the first step toward the control of the use of antibiotics in agro-food production, as it is a major source of bacterial resistance acquisition [ 87 ]. Phages were used to protect dairy products [ 88 ], fruits [ 89 ], vegetables [ 90 ], meat [ 91 ], and fish [ 92 ]. Developments in the utilization of phages as antimicrobial agents in plant and animal agriculture at the farm level are summarized in a recent review by Svircev et al [ 93 ].…”

Responses of Escherichia coli and Listeria monocytogenes to ozone treatment on non-host tomato: Efficacy of intervention and evidence of induced acclimation

“…Strategies including on-farm hygiene, decontamination by washing, film coating, prophage induction, and the use of chemical interventions that involve sodium hypochlorite (NaClO), sodium chlorite (NaClO 2 ), acidified NaClO 2 , acidified sodium benzoate (NaB), or peracetic acid (PAA) are common means for post-harvest control of bacterial contamination on fresh tomatoes and other types of vegetables [ 12 – 14 ]. Ozone gas (O 3 ) has been widely used decontaminating agent for eliminating E .…”