Comparison of the phylogenetic analysis of PFGE profiles and the characteristic of virulence genes in clinical and reptile associated Salmonella strains

Abstract

Background: Salmonella is generally considered as a human pathogen causing typhoid fever and gastrointestinal infections called salmonellosis, with S. Enteritidis and S. Typhimurium strains as the main causative agents. Salmonella enterica strains have a wide host array including humans, birds, pigs, horses, dogs, cats, reptiles, amphibians and insects. Up to 90% of reptiles are the carriers of one or more serovars of Salmonella. Extraintestinal bacterial infections associated with reptiles pose serious health threat to humans. The import of exotic species of reptiles as pet animals to Europe correlates with the emergence of Salmonella serotypes, which not found previously in European countries. The presented study is a new report about Salmonella serotypes associated with exotic reptiles in Poland. The goal of this research was to examine the zoonotic potential of Salmonella strains isolated from reptiles by comparative analysis with S. Enteritidis strains occurring in human population and causing salmonellosis.

Results: The main findings of our work show that exotic reptiles are asymptomatic carriers of Salmonella serovars other than correlated with salmonellosis in humans (S. Enteritidis, S. Typhimurium). Among the isolated Salmonella strains we identified serovars that have not been reported earlier in Poland, for example belonging to subspecies diarizonae and salamae. Restriction analysis with Pulsed-field Gel Electrophoresis (PFGE), showed a great diversity among Salmonella strains isolated from reptiles. Almost all tested strains had distinct restriction patterns. While S. Enteritidis strains were quite homogeneous in term of phylogenetic relations. Most of the tested VGs were common for the two tested groups of Salmonella strains.

Conclusions: The obtained results show that Salmonella strains isolated from reptiles share most of virulence genes with the S. Enteritidis strains and exhibit a greater phylogenetic diversity than the tested S. Enteritidis population.

Keywords: PFGE profiles; RAS; Salmonella; Zoonotic potential.

Fig. 1

Genetic relatedness and VGs profiles of Salmonella strains isolated from humans and reptiles. * Strains PCM 2951 and PCM 2952 were nontypeable with PFGE method. ** Molecular Weight Marker. *** White square - lack of virulence gene, black square - presence of virulence gene

Fig. 2

Percentage layout of detected VGs among Salmonella strains isolated from humans and reptiles

Fig. 3

GLC-MS/MS analysis of NeuAc (sialic acid) content. a Tested Salmonella Hvittingfoss PCM 2946 strain; b Control: Hafnia alvei PCM 2386. MS/MS simultaneous analysis of Kdo (marker ion of m/z = 195), NeuAc (ion of m/z = 386), and perseitol (ion of m/z = 128) as an internal standard (IS)