Control of Salmonella Newport on cherry tomato using a cocktail of lytic bacteriophages

Citation

El-Dougdoug, N.K., Cucic, S., Abdelhamid, A.G., Brovko, L., Kropinski, A.M., Griffiths, M.W., Anany, H. (2019). Control of Salmonella Newport on cherry tomato using a cocktail of lytic bacteriophages. International Journal of Food Microbiology, [online] 293 60-71. http://dx.doi.org/10.1016/j.ijfoodmicro.2019.01.003

Plain language summary

Bacteriophages (bacteria eaters) have been envisioned as tools to control a variety of foodborne pathogenic bacteria and ensure ensure a safe and secure food supply. Salmonella is a global foodborne pathogen that is a threat to public health around the world. Contaminated tomatoes have been associated with several Salmonella outbreaks. This research investigated using phages to control the growth of Salmonella Newport, as one of top ten Salmonella serovars associated with human salmonellosis in North America, on cherry tomatoes. Four lytic bacteriophages against Salmonella Newport were isolated from environmental samples and characterized. They were found to be stable at different temperatures and pH and suitable for food application. Complete inhibition of bacterial growth in liquid medium was observed at 25 °C for 24 h. In addition, a 4.5 log10 unit reduction in the bacterial count was observed when applying the phage cocktail onto contaminated tomatoes stored at 25°C for 3 days. These findings suggest that the isolated phages can be used for biocontrol of S. Newport to improve the safety of RTE produce.

Abstract

Bacteriophages have been envisioned as tools to control a variety of foodborne pathogenic bacteria. Salmonella is a foodborne pathogen that is a threat to public health around the world. Contaminated tomatoes have been associated with several Salmonella outbreaks. Hence, the objective of this work was to identify and characterize different lytic bacteriophages against Salmonella Newport, as one of top ten Salmonella serovars associated with human salmonellosis in North America, and then apply these phages to enhance the safety of cherry tomatoes. Four lytic phages against Salmonella Newport were selected based on their ability to lyse a majority of the 26 screened Salmonella serovars. The selected phages belong to Myoviridae (vB_SnwM_CGG4-1, vB_SnwM_CGG4-2) and Siphoviridae (vB_SnwM_CGG3-1, vB_SnwM_CGG3-2) families. They were found to be stable at different temperatures and pH, have latent periods ranging from 53 to 65 min and burst sizes from 92 to 177. In addition, the two Myoviridae phages have a lower frequency of developing bacteriophage insensitive mutants when compared with the Siphoviridae phages. No significant change in virulence gene expression was observed in the developed bacteriophage insensitive mutants when compared to the parental phage sensitive strain. Furthermore, the vB_SnwM_CGG4-1 genome revealed no homology to virulence or lysogenic genes. A phage cocktail was used to control the growth of S. Newport in broth medium and on contaminated cherry tomato. Complete inhibition of bacterial growth in broth medium was observed at 25 °C for 24 h. In addition, a 4.5 log 10 unit reduction in the bacterial count was observed when applying the phage cocktail onto contaminated tomatoes stored at 22 °C for 3 days. These findings suggest that the isolated phages can be used for biocontrol of S. Newport to improve the safety of ready-to-eat (RTE) produce.

Publication date

2019-03-16

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