Location: Produce Safety and Microbiology ResearchTitle: Complete genome sequences of two Shiga toxin-producing Escherichia coli strains isolated from crows
Submitted to: Microbiology Resource Announcements
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2019
Publication Date: 11/7/2019
Citation: Carter, M.Q., Pham, A.C., Carychao, D.K., Cooley, M.B. 2019. Complete genome sequences of two Shiga toxin-producing Escherichia coli strains isolated from crows. Microbiology Resource Announcements. 8(45):e01082-19. https://doi.org/10.1128/MRA.01082-19.
Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) is one of the main bacterial causal agents of foodborne illness outbreaks associated with fresh produce. STEC naturally resides in ruminant animals; however, diverse STEC strains have been isolated from birds, implying that birds might be an environmental source of STEC transmission. Escherichia coli strains RM9088 and RM10410 were isolated from crows near a leafy greens-growing region in California in April and July of 2009, respectively. Both strains carry genes encoding Shiga toxins and other virulence factors in enteric pathogens. To better understand the pathogenicity of avian STEC, we sequenced the genomes of the crow isolates and performed comparative genomic analysis. Our study revealed that both avian STEC strains appeared to be a hybrid of STEC and entertoxigenic E. coli (ETEC) as both strains carry genes encoding heat-stable toxins. Further studies are needed to better understand the pathogenicity of such STEC/ETEC strains and the potential public risk posed by the avian STEC.
Technical Abstract: Comparative analysis of the two Shiga toxin-producing Escherichia coli strains isolated from crows revealed the virulence potential of avian STEC. Strain RM9088 carries stx genes encoding Shiga toxin 1a and a typical pEHEC, containing genes (hlyCABD) encoding enterohemolysin. Unexpectedly, strain RM9088 also carries genes (astA and sta1) encoding heat-stable toxins, a common virulence factor of enterotoxigenic E. coli (ETEC). Unlike RM9088, strain RM10410 carries two sets of stx encoding Stx1a and Stx2d, respectively. Although RM10410 lacks genes encoding enterohemolysin, it is positive in genes encoding heat-stable toxin, similarly to RM9088. Thus both avian STEC strains are a hybrid of STEC and ETEC, representing a new pathovar of E. coli.