Prevalence, risk factors and genetic traits of Salmonella Infantis in Dutch broiler flocks

Salmonella Infantis is a poultry-adapted enterica serovar that increasingly reported in broilers and also regularly identified among human salmonellosis cases. An emerging S. mega-plasmid (pESI), carrying fitness, virulence antimicrobial resistance genes, found. We investigated the prevalence, genetic characteristics risk factors for (pESI-carrying) broilers. Faecal samples from 379 broiler flocks (in 198 farms with ?3000 birds) Netherlands were tested. A questionnaire about farm was administered. Sampling performed July 2018-May 2019, three weeks before slaughter. Fourteen 10 farms) Infantis-positive, resulting 3.7 % flock-level 5.1 farm-level prevalence. Based on multi-locus sequence typing (MLST), all isolates belonged to type 32. All but one isolate carried pESI-like mega-plasmid. Core-genome MLST showed considerable heterogeneity isolates, even within same farm, few small clusters detected. The typical pESI-borne multi-resistance pattern aminoglycosides, sulphonamide tetracycline (93 %), as well trimethoprim (71 Additionally, (fluoro)quinolones based gyrA gene mutations found more often using salinomycin coccidiostat, where flock thinning applied or litter quality poor, whereas employing external cleaning companies, wheat feed, vaccination against infectious bronchitis, protective. Suggestive evidence vertical transmission hatcheries heterogeneous population has established itself Dutch flocks, calling further monitoring of its spread comprehensive appraisal control options.