Is Shiga toxin-producing Escherichia coli O45 no longer a food safety threat? The danger is still out there

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

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2020
Publication Date: 5/22/2020
Citation: Zhang, Y., Liao, Y., Sun, X., Wu, V.C.H. 2020. Is Shiga toxin-producing Escherichia coli O45 no longer a food safety threat? The danger is still out there. Microorganisms. 8(5):782. https://doi.org/10.3390/microorganisms8050782.
DOI: https://doi.org/10.3390/microorganisms8050782

Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) is one of the major foodborne pathogens and can cause several human diseases, such as hemolytic uremic syndrome. The most common serogroups associated with foodborne outbreaks include STEC O26, O45, O103, O111, O121, O145, and O157. Previous studies have investigated the pathogenicity and evolution of STEC serogroups based on their genomic information. However, similar information about STEC O45 is lacking. Here, we reported the whole-genome sequencing data of four STEC O45 pathogens, including three environmental E. coli O45:H16 strains (RM11911, RM13745, and RM13752) and one clinical E. coli O45:H2 strain (SJ7). Subsequently, to investigate their evolutionary evidence, the genomic information of these four STEC O45 strains was compared with that of 11 reference STEC strains from the clinical origin. The results showed that three E. coli O45:H16 and one E. coli O45:H2 strains had an average of 5,184 genes and contained one or two plasmids. Furthermore, the results showed that the clinical E. coli O45:H2 strains were more pathogenic than the environmental E. coli O45:H16 strains due to the presence of more virulence genes in the genome of E. coli O45:H2. Additionally, the genomic evidence demonstrated that E. coli O45:H2 had a common evolutionary lineage with E. coli O103:H2 rather than with E. coli O45:H16 strains. The findings of this study provide valuable genomic information to facilitate the surveillance of STEC O45.

Technical Abstract: Non-O157 Shiga toxin-producing Escherichia coli (STEC) strains have been frequently associated with foodborne outbreaks. With the improvement of the next-generation sequencing technology, many STEC strains, including the serogroups of O157 and top 6 non-O157, have been sequenced to facilitate the characterization. However, the information regarding the genomic characterization of STEC O45 strains is scarce. The objectives of this study were to genomically characterize four different STEC O45 strains of either environmental or clinical origin and to determine evolutionary relatedness with other serotypes of STEC strains. Three environmental E. coli O45:H16 strains (RM11911, RM13745, and RM13752) and one clinical E. coli O45:H2 strain (SJ7) were subjected to whole-genome sequencing in this study. Together with two additional reference E. coli O45:H2 strains, all six STEC O45 strains were further used to characterize virulence factors and mobile genetic elements of STEC O45. Subsequently, comparative genomics analysis was conducted among these six STEC O45 strains and nine additional reference STEC strains with different serotypes isolated from clinical or outbreak samples to evaluate their evolutionary relationship. The results showed that each of three environmental E. coli O45:H16 strains contained a Stx1 prophage and one or two virulence plasmids, while each of three clinical E. coli O45:H2 strains contained one or two Stx prophages, one locus of enterocyte effacement (LEE) pathogenicity island, and one virulence plasmid. The results of the whole-genome-based phylogenetic analysis showed that 15 STEC pathogens from different sources were divided into 5 clusters. Furthermore, E. coli O45:H2 strains shared a common evolutionary lineage with E. coli O103:H2, but were phylogenetically different from E. coli O45:H16 strains. Moreover, the comparative genomics showed that most of E. coli O45:H2 and E. coli O103:H2 strains shared high sequence homology on certain mobile virulence elements, such as Stx1a prophages. The findings of this study provide valuable insights into the genomic characterization, pathogenicity, and evolution of STEC O45 strains to facilitate the surveillance of STEC.