The phylogenetic and phenotypic analysis of Salmonella enterica serovar Weltevreden

Diarrhoeal diseases remain a global health threat and are responsible for high levels of morbidity and mortality worldwide, with an estimated 1.7 billion cases every annum. Additionally, according to the World Health Organisation, diarrhoeal diseases are the second leading cause of death in children under 5 years old. Salmonella are one of the most common diarrhoeal pathogens [1] (WHO Accessed 20 February 2015) with serovars Enteritidis, Typhimurium and Typhi playing a major role in outbreaks worldwide. However, Salmonella enterica serovar Weltevreden (S. Weltevreden) has recently attracted a great deal of interest due to increasing reports of its isolation by reference laboratories around the world, with a particular high incidence in South East Asia. However, relatively little is known about the genotypic or phenotypic properties of this understudied serovar. In this study, phylogenetics and comparative genomics based on whole genome sequences were used to define the genetic diversity within a sizeable collection of S. Weltevreden isolates collected from across the globe, with a focus in South East Asia. This phylogenetic analysis confirmed that the S. Weltevreden isolates belong to a monophyletic clade formed of several sub-clades presenting distinct geographical clustering and characteristics. Phenotypic characterisation was performed on selected isolates, with an aim to dissect aspects of host-pathogen interaction during infection, providing a foundation to compare S. Weltevreden with other serovars such as S. Typhimurium. Interestingly, an overall attenuated pathology was observed both invitro (hep 2 cell line) and in-vivo (murine and zebrafish embryos) for S. Weltevreden compared to the S. Typhimurium reference strain. This is the first report of the phylogenetic analyses of S. Weltevreden and of a systematic in-vitro and in-vivo characterisation of the sub-species.