Some aspects of molecular epidemiology & characterisation of Salmonella Typhimurium isolated from man & animals.

BACKGROUND & OBJECTIVES: Salmonellae are widely distributed in nature and cause a wide spectrum of diseases in man and animals. Among the different serovars of Salmonella enterica, S. Typhimurium is most commonly associated with enteric infection in man and animals. The present paper reports on the phage typing, plasmid profile, antimicrobial resistance and genetic diversity of Indian strains of S. Typhimurium isolated from man and animals.

METHODS

A total of 17 strains of S. Typhimurium were subjected to phage typing and tested for plasmid and antimicrobial resistance. Genetic variability of the strains was studied by cleaving the whole cell DNA with restriction endonuclease, XbaI and detecting the restriction fragments by pulse-field gel electrophoresis (PFGE).

RESULTS

All the 17 strains were typeable and belonged to 4 phage types (DT003, DT004, DT096 and DT193). Three plasmid profiles were observed. Multiresistance was common. Strains belonged to DT193 were highly resistant to most of the antimicrobial agents tested and harboured 3-4 plasmids. Strains belonged to DT003, DT004 and DT096 were found to be less resistant to antibiotics and harboured only 1 plasmid. A genetic variability was observed among the strains irrespective of the source of isolation. Twelve restriction patterns observed among the 17 strains as analyzed by PFGE indicated a considerable genetic heterogeneity among human and animal isolates.

INTERPRETATION & CONCLUSION: A relationship was observed between resistance patterns, plasmid profiles and phage typing. Restriction analysis obtained by PFGE was found to be more discriminating in the differentiation of strains than the other methods used, and thus provides a valuable alternative tool for molecular characterisation of S. Typhimurium isolated from man and animals.