Investigation of environmental factors on the prevalence of free bacteriophages against Shiga toxin-producing Escherichia coli strains in produce pre-harvest environment in Salinas, California

Authors: Liao, Yen-Te; QUINTELA, IRWIN - University Of Maine; Nguyen, Kimberly; Salvador, Alexandra; Cooley, Michael; Wu, Vivian

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/23/2017
Publication Date: 2/23/2017
Citation: Liao, Y., Quintela, I., Nguyen, K.M., Salvador, A., Cooley, M.B., Wu, V.C. 2017. Investigation of environmental factors on the prevalence of free bacteriophages against Shiga toxin-producing Escherichia coli strains in produce pre-harvest environment in Salinas, California. Meeting Proceedings. 2017 USDA-ARS/FSIS Annual Food Safety Meeting. NCTC, Shepherdstown, WV. Section Z, P13.

Interpretive Summary:

Technical Abstract: Shiga toxin-producing E. coli (STEC) strains, commensal to gastrointestinal tracts of ruminants or other animals, have been associated with serious human illnesses and high mortality among immunocompromised populations. Along with the detection of STEC strains from fecal-contaminated environments such as feed lot or wastewater, studies also focus on bacteriophages harboring stx genes that contribute to virulence of the bacteria. However, little is known about the prevalence of lytic STEC-specific bacteriophages, which may mitigate the population of their bacterial hosts, in low fecal-contaminated environment. The objective of this research was to study the effects of environmental factors on the prevalence of free lytic STEC-specific bacteriophages and the association with their bacterial hosts in produce pre-harvest environment. Surface water collected from 17 different sites in Salinas California every other week from May to September 2016 were subjected to isolation of lytic bacteriophages using 4 generic E. coli and 28 pathogenic E. coli strains (4 strains each of O26, O45, O103, O111, O121, O145 and O157 serogroups) as host strains, as well as isolation of O157 and non-O157 STEC strains using immunomagnetic separation and selected media (CT-SMAC, NT-Rainbow, and Sheep blood agar), followed by confirmation using PCR-based methods. The information of geographical location and weather condition were collected. The results showed that the lytic STEC-specific (O121, O145, O157 and other serogroups) bacteriophages were isolated from 9 sites. Pathogenic O157 and non-O157 STEC were isolated from 8 sites. The STEC-specific bacteriophages were mostly isolated in late summer and early fall. STEC strains were isolated at a similar time period. However, there was a trend that the sites with isolation of certain bacteriophage were not likely shown with the isolation of bacteriophage host strains of the specific serogroups. In addition, most bacteriophage-positive sites were at the downstream of Salinas River system. The findings of the study indicate that the prevalence of lytic STEC-specific bacteriophages is negatively correlated with STEC strains in produce pre-harvest environment. Further studies are required to evaluate other ecological or biological factors contributing to the phenomenon, and the potential of the lytic STEC bacteriophages for STEC prevention in produce safety.