Molecular characterisation of salmonellae isolated from poultry

Abstract

Five serotypes of salmonellae from avian sources were examined for biochemical properties, serology, drug resistance, plasmids, restriction enzyme pattern of plasmid as well as genomic DNA and pathogenicity. The biochemical characters are in confirmity with the characters described for the serotypes by the earlier workers. The study of antibiogram with 20 antibiotics/chemotherapeutic agents revealed the presence of multiple drug resistance in all the five serotypes. In the plasmid analysis, S enteritidis and S. branderup were found to be plasmid free. The number of plasmids in other serotypes ranged from two to three and the size ranged from 1.75 kb to 48.32 kb. Identical low molecular weight plasmids were present in both S. gallinarum. The presence of large plasmid in one of the S. gallinarum did not confer any additional detectable resistance character. S. typhimurium contained two plasmids of sizes 13.62 kb and 4.2 kb. Restriction enzyme analysis of plasmid DNA from three salmonellae with EcoRl and Hindlll yielded three different restriction pattern with each enzyme. Ethidium bromide and exposure to elevated temperature cured the plasmids present in the salmonellae within two days and 14 days respectively. Acridine orange and sodium dodecyl sulphate were found to be ineffective in curing the

plasmid DNA. The elimination of plasmids resulted in the loss of resistance to antibiotics was demonstrated in S. typhimurium. In tests to assess the differences in pathogenicity between wild and cured isolates of S. typhimurium in day old chicks, only intraperitoneal route was found to be effective when compared to oral route. A relation of plasmids to virulence was noted only in S. typhimurium. Day old chicks were refractory to infection to S. gallinarum by both the routes. Plasmids encoding both resistance and virulence were observed in S typhimurium. Plasmid negative serotypes of S. enteritidis and S. branderup were found to be equally virulent as wild strains of S. typhimurium. So a definite correlation between virulence and plasmids could not be made. Restriction enzyme analysis of chromosomal DNA yielded bands which were indistinct and so uncomparable. Hence of the tests based on the analysis of genetic content plasmid profile was found ,to be efficient in typing the isolate rather than restriction enzyme analysis of genomic DNA.