Molecular characterisation of Salmonella typhimurium and Salmonella enteritidis by plasmid analysis and pulsed-field gel electrophoresis

Abstract number: 1733_84

Aktas Z., Day M., Bal C., Diren S., Threlfall E.

Aims: The aim of this study was to investigate clonal diversity of S. enteritidis and S. typhimurium isolates from various clinical samples in Turkey.

Materials and Methods: Fourty one strains of Salmonella spp. isolates from paediatric patients in Cerrahpasa Faculty of Medicine, Istanbul, Turkey, from 2001 to 2004 were examined for their susceptibility to various antibiotics and the presence of antibiotic resistance genes. Pulsed-field gel electrophoresis and plasmid profiling were used to characterise and determine possible genetic relationships between Salmonella enterica ssp. enterica isolates of clinical isolates.

Results: All the S. enteritidis strains (n = 26) were susceptible to antimicrobial agents tested, whereas one S. typhimurium (n = 15) was resistant to ampicilline, four strains were resistant to ampicilline, chloramphenicol, streptomycin, spectinomycin, sulphonamides and tetracyclines (R-type ACSSpSuT) and the remaining other isolates were susceptible to antimicrobial agents tested. R-type strains were positive for the intI gene and had only one plasmid of 60 Mda. Plasmid pattern analysis permitted further differentiation of the S. enteritidis strains into six groups. A serovar-specific virulence plasmid of 38 MDa was detected in all of S. enteritidis strains (except one strain). Plasmids, with molecular masses varying between 2.5 and 89 MDa, were found in 12 of the 15 of the S. typhimurium strains and five different plasmid patterns were determined. After the XbaI macrorestriction profiles, we observed 23 subtypes which were grouped into five main patterns for S. enteritidis and 15 PFGE profiles were observed among the S. typhimurium strains and four patterns (I, II, III, IV) were found. Plasmids from resistant strains were not transferred by conjugation recipient Escherichia coli cells. Pulsed-field gel electrophoresis and restriction enzyme digestion analysis of DNA revealed different restriction profiles and sizes, indicating these strains usually were not clonaly related whereas MDR-S. typhimurium isolates were clonaly related.

Conclusion: Our study demonstrated the emergence of multiresistant S. typhimurium DT104 infections in our hospital. Therefore, investigation of the antimicrobial susceptibilities, the characteristics of resistant strains and the molecular epidemiology of the strains is more significant. PFGE is more discriminatory and can be used as a confirmatory method.