Characterization of free lytic bacteriophages isolated from compost against O145 Shiga toxin-producing Escherichia coli (STEC) as a potential biocontrol agent

Authors: Liao, Yen-Te; Salvador, Alexandra; LIU, FANG - Ocean University Of China; Bates, Anne; Wu, Vivian

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Shiga toxin-producing E. coli (STEC), one of the most prevalent foodborne pathogens, are notorious for hemolytic uremic syndrome (HUS) and causing high mortality among children and the elder population after infection. Besides O157 STEC, non-O157 STEC—particularly serogroup O145—is commonly associated with produce outbreaks in the United States. Bacteriophages have been investigated as an intervention to prevent pathogen contamination due to their mitigating effect. STEC phages are commonly isolated from feces-contaminated environment because of the natural reservoir of their bacterial hosts. In addition, lytic phages are likely used in post-harvest environment due to easier application than pre-harvest setting. Little is known regarding phages isolated from non-fecal environment and its potential for produce pre-harvest intervention. The objective of this research was to determine physiological and genomic characteristics of a lytic phage isolated from non-fecal compost samples for its potential biocontrol function against O145 STEC in produce pre-harvest environment. Using culture and spot test methods, bacteriophage specifically against O145 host strains from non-fecal compost sample was isolated and designated as P145C phage. Physiological characterization including phage morphology, absorption rate, one-step growth curve, and efficacy of plating (E.O.P) against various O145 STEC strains were conducted. The phage DNA was further subjected to whole genome sequencing (WGS, Illumina Miseq Reagent kit 600 cycle v3), followed by analyses of de novo genome assembly, and whole genome annotation. The result showed that P145C, belonging to Siphoviridae family, was highly lytic against most O145 STEC strains previously isolated from produce-growing environment. The absorption time and latent period were approximately 10 min and 20 min, respectively, with burst size of 898 pfu per infected cell. The WGS analysis indicated this is a novel phage containing double-stranded, circular genome size of approximate 42031 bp (49.1 mol% G+C). No virulence factors such as stx genes was identified. The finding of this study suggests that P145C phage is a good candidate as a biocontrol agent for O145 STEC strains in pre-harvest setting due to short absorption time, large burst size and the high specificity. Further studies are required to evaluate the application on different crops to facilitate the antibacterial effectiveness.