Occurrence of a New Variant of Salmonella Infantis Lacking Somatic Antigen

Salmonella Infantis is one of the most frequent serovars reported in broilers and is also regularly identified in human salmonellosis cases, representing a relevant public health problem. In the laboratories of the Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata (IZSPB), six Salmonella Infantis strains with antigenic formula -:r:1,5 have been isolated from the litter and carcass of broilers between 2018 and 2022. The strains were investigated to evaluate their phenotype, antibiotic resistance and genomic profiles. Genomic analysis confirmed that the isolates belonged to the Infantis serotype and to the sequence type ST32. Moreover, all strains showed a multidrug-resistant (MDR) profile and were characterised by the presence of the IncFIB plasmid incompatibility group. Three strains had the (CTX)-C-bla-M-1 gene, and one of them carried IncX1. The presence of this new variant of S. Infantis is particularly relevant because it could expand the landscape of the S. Infantis population. The absence of the somatic antigen could pose a problem in both isolation and serotyping and a consequent public health concern due to the spread of Salmonella infection.

Automated summary

Salmonella Infantis is a common serovar in broilers and human salmonellosis cases. Six strains of Infantis were isolated from broiler litter and carcasses between 2018 and 2022 and were characterized for their phenotype, antibiotic resistance, and genomic profiles. The results showed that these strains were multidrug-resistant and belonged to the Infantis serotype and sequence type ST32. The presence of a new variant of S. Infantis is significant as it may expand the population and pose a public health concern.