A LARGE SALMONELLA ENTERITIDIS OUTBREAK IN ISRAEL CAUSED BY AN EMERGING CLONE

In this report we describe a large Salmonella outbreak in Israel, caused by an emerging clone of S. Enteritidis during October-December 2015.

Clinical, veterinary and food laboratories submit Salmonella isolates to the National Salmonella Reference laboratory (NSRL) at the Government Central laboratories for confirmation and further characterization. Representative samples of the outbreak strain and historical S. Enteritidis human strains were subjected to antimicrobial susceptibility testing (disk diffusion and VITEK2), Pulsed Field Gel Electrophoresis (PFGE) and whole genome sequencing (WGS). S. Enteritidis strains isolated from poultry and from a variety of food products were also tested for the same parameters.

During October-November 2015, 1026 Salmonella clinical isolates were received at the NSRL, and 624 (61%) of them were serotyped as S. Enteritidis. These numbers indicated a dramatic increase compared to only 18% in 2014. PFGE analysis revealed that 76% ( 60 isolates) belonged to one unique cluster. The specific genotype had never been detected in Israel before October 2015. Further characterization of the new strain revealed susceptiblity to commonly prescribed antibiotics tested. This clone was not observed in a collection of S. Enteritidis isolates from poultry , including vaccine strains. The WGS of representitive isolates is currently analysed in order to be compared to the international database. Results obtained couid assist in in source detection and help reveal virulence factors and specific features of this clone .

To date, epidemiologic, laboratory, and traceback investigations have not identified the source of infection. The sudden massive emergence of a new salmonella strain, possibly derived from an unknown food item indicates the vulnerability of the food chain. This outbreak demonstrates the need for the multilayered data generated at the national reference laboratories for in depth analysis.