Investigating the whole-genome sequences of a new locus of enterocyte effacement-positive Shiga toxin-producing Escherichia coli O157:H7 strain isolated from river water

Authors: ZHANG, YUJIE - Shanghai Ocean University; Liao, Yen-Te; Salvador, Alexandra; SUN, XIAOHONG - Shanghai Ocean University; Wu, Vivian

Submitted to: Microbiology Resource Announcements
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2020
Publication Date: 3/19/2020
Citation: Zhang, Y., Liao, Y., Salvador, A., Sun, X., Wu, V.C. 2020. Investigating the whole-genome sequences of a new locus of enterocyte effacement-positive Shiga toxin-producing Escherichia coli O157:H7 strain isolated from river water. Microbiology Resource Announcements. 9(12):e00112-20. https://doi.org/10.1128/MRA.00112-20.
DOI: https://doi.org/10.1128/MRA.00112-20

Interpretive Summary: Shiga toxin-producing E. coli (STEC) is one of the major foodborne pathogens that can cause several human diseases. E. coli O157:H7, as one of the most notorious STEC strains, is frequently associated with multiple foodborne outbreaks in the United States. Previous studies demonstrated that rivers contaminated with animal waste are a distributing source of pathogenic STEC strains on produce farms through irrigation system, rain precipitation, and underground water. Here, we report the whole-genome sequence of a new STEC O157:H7 strain, RM19259, isolated from the Mississippi River watershed in 2016. This STEC O157 strain contains a bacterial genome with a total of 5,440 predicted genes encoding numerous proteins, including several crucial ones associated with the pathogenicity of the STEC strain. Moreover, most genes encoding key virulence proteins were found in the elements within the bacterial genome that are likely to be transferred to other susceptible strains, resulting in the potential emergence of new pathogens. The findings of this study provided additional information of a new pathogenic E. coli O157:H7 isolated from surface water that can be used to facilitate epidemiological surveillance of STEC O157:H7 contamination.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) is one of the major bacterial pathogens associated with numerous foodborne outbreaks around the world. In particular, E. coli O157:H7 has been the most persistent pathogens in STEC-associated outbreaks causing severe human illnesses. Previous studies showed diverse STEC strains have been isolated from several environmental samples, such as animal feces, leaf green, and soil. Moreover, rivers were considered as a distributing source of STEC due to its association with the aforementioned environmental factors. Thus, we report the complete genome sequence of E. coli O157:H7 RM19259 strain previously isolated from the Mississippi river watershed in 2016 to unveil the pathogenicity of the strain. The strain RM19259 contains a 5,511,015-bp chromosome (GC content of 50.5%) and a 98,304-bp plasmid. The chromosome encodes a total of 5,440 predicted protein-coding sequences (CDSs), 22 rRNA, and 106 tRNAs. RM19259 is an E. coli O157:H7 strain that harbors two sets of stx genes, including one stx2a located on an 83,266-bp prophage and one stx2c located on a 35,769-bp prophage. Additionally, a 41,255-bp locus of enterocyte effacement (LEE) pathogenicity island was identified in the chromosome of RM19259, which also carried enterohemorrhagic E. coli (EHEC)-associated virulence genes that encode Type III translocated protein (nleA, nleB, nleC, espJ, tir, tccP) and adherence (eae and iha). Interestingly, the strain contains a virulence gene, EAST-1 heat-stable toxin (astA), commonly related to enterotoxigenic E. coli (ETEC). The plasmid pRM19259 is a typical F-like plasmid pO157, which contains several virulence-related genes, such as ehxA (enterohaemolysin), espP (serine protease), etpD (Type II secretion protein), katP (catalase-Peroxidase), and toxB (Toxin B). The findings of this study provide valuable insights into the epidemiological surveillance of E. coli O157:H7 infections.