Abstract
Salmonella is a leading cause of bacterial infections in animals and humans. We sequenced a collection of 450 Salmonella strains from diseased animals to better understand the genetic makeup of their virulence and resistance features. The presence of Salmonella pathogenicity islands (SPIs) varied by serotype. S. Enteritidis carried the most SPIs (n = 15), while S. Mbandaka, S. Cerro, S. Meleagridis, and S. Havana carried the least (n = 10). S. Typhimurium, S. Choleraesuis, S. I 4,5,12:i:-, and S. Enteritidis each contained the spv operon on IncFII or IncFII-IncFIB hybrid plasmids. Two S. IIIa carried a spv operon with spvD deletion on the chromosome. Twelve plasmid types including 24 hybrid plasmids were identified. IncA/C was frequently associated with S. Newport (83%) and S. Agona (100%) from bovine, whereas IncFII (100%), IncFIB (100%), and IncQ1 (94%) were seen in S. Choleraesuis from swine. IncX (100%) was detected in all S. Kentucky from chicken. A total of 60 antimicrobial resistance genes (ARGs), four disinfectant resistances genes (DRGs) and 33 heavy metal resistance genes (HMRGs) were identified. The Salmonella strains from sick animals contained various SPIs, resistance genes and plasmid types based on the serotype and source of the isolates. Such complicated genomic structures shed light on the strain characteristics contributing to the severity of disease and treatment failures in Salmonella infections, including those causing illnesses in animals.
Highlights
More than 2600 serotypes are recognized in Salmonella
Dublin strains isolated from human, sick bovine and retail beef along with other serotypes, and the results showed that all the strains regardless of serotype carried Salmonella pathogenicity islands (SPIs)-1 to 6, and 11
To elucidate genomic features of virulence, we performed comparative genomic analysis of Salmonella strains isolated from diseased animals
Summary
Almost 99% of the serotypes associated with disease in warm-blooded animals and humans are members of Salmonella enterica subspecies enterica (subspecies I) [1]. They commonly elicit localized self-limiting inflammation of the terminal ileum and colon known as gastroenteritis in humans, and are able to colonize and infect a broad range of animal species. Animal infections by this subspecies are asymptomatic; some serotypes can cause symptomatic disease, which is dependent on the infecting serotype and the species, genetic background, and immune status of the host. It is well known that the genetic background of pathogens plays a critical role in contributing to infection outcomes [2,3,4]. Typhimurium can cause acute enteritis and septicemia in pigs and cattle yet colonizes the intestines of adult poultry asymptomatically [5]
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