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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #359848

Research Project: Ecology and Detection of Human Pathogens in the Produce Production Continuum

Location: Produce Safety and Microbiology Research

Title: Prediction, diversity, and genomic analysis of temperate phages induced from Shiga toxin-producing Escherichia coli

Author
item Zhang, Yujie - Shanghai Ocean University
item Liao, Yen-te
item Sun, Xiaohong - Shanghai Ocean University
item Wu, Vivian

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/29/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC), particularly with the serogroups of O157 and top six non-O157, caused numerous foodborne outbreaks, including the recent outbreaks associated with STEC O157-contaminated romaine lettuce in California. Previous studies found that some bacterial species, Vibrio and Ochrobactrum, contain one or few prophages carrying virulence genes together with other prophages of different functions in the bacterial genome. Nevertheless, information regarding the diversity of prophages present in STEC genomes is lacking. The objectives of this study were to predict the presence and diversity of prophage in the different serotyping STEC genomes, and to evaluate the effects of different conditions on the induction of Shiga toxin-converting phages. Forty complete STEC genomes were downloaded from NCBI and subjected to prophage prediction using PHASTER. Eight of the STEC strains with different serogroups were selected for evaluating the induction methods by using different antibiotics, temperatures, and UV exposure times. The induction level of Stx phages was accessed using quantitative real-time polymerase chain reaction (qPCR). Plaque size of the induced phages was also obtained. Three induced phages were confirmed with the presence of stx using conventional PCR and were subsequently subjected to whole genome sequencing using Illumina Miseq as comparison with the predicted results. Results showed that there were 4 to 19 intact prophages in each STEC genome from which one or two prophages encode stx genes. Stx1 prophage was easily induced by mitomycin C, whereas Stx2 prophage was likely induced by UV. Additionally, the induced phage ly157Nzw produced the large plaque, indicating strong lysing activity. Both phages ly157V1zw and ly157V2zw encoding stx2 gene were able to convert the generic E. coli to a new pathogen through the transfer of stx2 after infection. The findings of the study show that diverse prophages are present in STEC genomes. Additionally, the prophages coding for stx genes in STEC strains could potentially contribute to emergence of new pathogens by the transfer stx genes to other commensal strains after induction by environmental stress, such as exposure to solar radiation or antibiotics.