3 years ago

Molecular prediction of the O157:H- phenotype prevalent in Australian STEC cases improves the concordance of in silico serotyping with phenotypic motility.

Flavia Huygens, Amy V Jennison, Irani U Rathnayake, Christine J D Guglielmino, Alexander P Pintara
Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen, where serotype O157:H7 is typically associated with severe disease. Australia is unique in its STEC epidemiology as severe cases are typically associated with non-O157 serogroups, and locally acquired O157 isolates are H-negative/non-motile. The H-negative phenotype and reduced severity of disease when compared to H7/motile strains are distinct features of O157 Australian strains but the molecular mechanism behind this phenotype has not been reported. Accurate characterisation of the H-negative phenotype is important in epidemiological surveillance of STEC. Serotyping is moving away from phenotypic-based methods as next generation sequencing allows rapid extrapolation of serotype through in silico detection of O-antigen processing genes, wzx,wzy, wzm and wzt, and the H-antigen gene, fliC The detection and genotyping of fliC alone is unable to determine the motility of the strain. Since most Australian O157:H-negative strains carry a H7 genotype yet phenotypically are non-motile, many are mischaracterised as H7 by in silico based serotyping tools. Comparative genomics of flagella genes between Australian and international isolates was performed and an insertion at 125 nt in flgF was identified in H-negative isolates. Chi-square results showed this insertion was significantly associated with the H-negative phenotype (p < 0.0001). Phylogenetic analysis was also completed to show that the Australian H-negative isolates with the insertion in flgF represent a clade within the O157 serogroup, distinct from O157:H7 serotypes. This study provides a genetic target for inferring the non-motile phenotype of Australian O157 STEC, which increases the predictive value of in silico serotyping.

Publisher URL: http://doi.org/10.1128/JCM.01906-17

DOI: 10.1128/JCM.01906-17

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