Persistence and epidemiological relevance of Salmonella enterica Newport in public-access waters from a central California coastal agricultural region

Salmonella enterica Newport is one of the most common serotypes linked to fresh produce-associated salmonellosis outbreaks in the United States. In this study, we examined the genetic diversity and epidemiological relevance of 20 Newport strains recovered from Salinas Valley watersheds between 2012 and 2016. Multilocus Sequence Typing (MLST) identified two sequence types (STs), with ST118 representing 70% of isolates and ST45 comprising the remainder. Core-genome MLST (cgMLST) resolved 12 cgSTs, with cgST132506 being the most common. Phenotypic analyses revealed lineage-specific traits, including enhanced biofilm formation and reduced river-water survival in cgST132506 strains. Additionally, ST45 strains adhered significantly better to cantaloupe rind but produced less biofilm on glass surfaces compared with ST118 strains. Epidemiological relevance was assessed by examining matched strains in identified Single Nucleotide Polymorphism (SNP) clusters using the Pathogen Detection pipeline. Two strains were classified as persistent (>500 matches), six as intermediate (50-500), and twelve as transient (<50). Persistent and intermediate strains, considered strains of concern (SOCs), were genomically related to known outbreak strains and widely detected across the United States, including those linked to the 2012 cantaloupe-associated outbreak and the 2017 watermelon-associated outbreak. Although no significant difference in attachment to cantaloupe rind was observed between SOCs and transient strains, SOCs displayed greater river-water survival, while transient strains produced significantly more biofilm. Diverse Newport strains were isolated from the two watersheds examined, and multiple SOCs were recovered from three locations, highlighting the need for targeted investigations into contamination sources in these areas.