Detection of class 1 integrons in Salmonella Weltevreden and silent antibiotic resistance genes in some seafood-associated nontyphoidal isolates of Salmonella in south-west coast of India

Aims: To study the antibiogram of 40 seafood isolates of Salmonella and use of PCR to detect the presence of integrons and genes coding for antibiotic resistance. Methods and Results: In this study, 40 isolates of Salmonella were used for antibiogram analysis. The multidrug-resistant isolates were analyzed for the presence of integron using integron-specific primers. Twenty-five percentage of the isolates were multidrug resistant while 67.50% were resistant to at least two antibiotics. Antibiotic resistance genes catA1 and tetA were present in 57.52 and 60%, respectively. Although widespread presence of genes was observed, only 26.08% of the catA1-carrying isolates exhibited phenotypic resistance against the respective antibiotic. Integrons present in representative isolates of Salmonella Weltevreden and Salmonella Newport were sequenced. The former contained class 1 integron with a single gene dfrA7 in the integron cassette and an adjacent dihydropteroate synthetase gene along with the usual quaternary ammonium compound resistance gene, while the later contained class 1 integron with dhfrA1, OrfC, in the integron cassette and an adjacent dihydropteroate synthetase gene along with the usual quaternary ammonium compound resistance gene. Conclusions: This study demonstrates the presence of silent antibiotic resistance genes and class I integrons in seafood-associated Salmonella strains. The study also demonstrates the first report of class I integron in Salm.similar to Weltevreden. Detection of catA1 genes in phenotypically sensitive bacteria suggests that these could be reservoirs in the environment. Significance and Impact of the Study: The manuscript provides novel results describing the existence of a high rate of antibiotic resistance in the Salmonella populations prevailing in environmental sources as well as an absence of correspondence between the presence of antibiotic resistance genes, and the exhibition of a the corresponding phenotypic trait of resistance against the respective antibiotic compound was observed. In addition, the manuscript reports the presence of the class I integron in Salm.similar to Weltevreden.