Abstract
Salmonella enterica has been documented as one of the leading causes of salmonellosis throughout the world and is most commonly associated with the consumption of contaminated food products. Thus, this research was aimed at studying the antimicrobial susceptibility pattern and detection of quinolone resistance in Salmonella spp isolated from food of animal origin. Thirty-six Salmonella isolates comprising 8 from poultry and 28 from seafood (clams) were identified, serotyped and characterized for their antimicrobial susceptibility against 10 different antibiotics. Plasmid DNA was isolated from all the isolates by alkaline lysis, quinolone resistant non-typhoidal S. Weltevreden were examined for mutation in the DNA gyrase coding gene. Among the 36 Salmonella isolates, 20 were S. weltevreden (8 from poultry and 12 from seafood) and 16 were S. Typhimurium (from seafood). All the isolates showed multiple resistance to nalidixic acid, tetracycline, co-trimoxazole and nitrofurantoin, but, interestingly, the isolates were 100% susceptible to ampicillin, chloramphenicol and gentamicin. Resistant isolates from the study carried the genes responsible for resistance to respective antibiotics. The strain S130 isolated in the study showed single point mutation, Asp87Gly, at position 87 in quinolone resistance determining region. It revealed mutation in quinolone resistance determining region as a cause for quinolone resistance in non-typhoidal Salmonellae. The occurrence of genes accountable for plasmid mediated resistance to quinolones (viz., qnrA, qnrB and qnrS) in plasmid of non-typhoidal Salmonellae isolates provides evidence for plasmid mediated quinolone resistance.
Highlights
Non-typhoidal Salmonellae (NTS) has emerged as a major group of foodborne pathogens which causes gastroenteritis, septicaemia, endocarditis and subsequent infections like intra-abdominal infections, and pulmonary infections[1]
Identification of bacterial strain and antimicrobial susceptibility tests All the 36 strains isolated from different sources in the study were identified as Salmonella spp. by conventional methods and confirmed by polymerase chain reaction (PCR) for invA and hns gene by yielding a product of 284 bp and 156 bp, respectively (Fig. 1)
All 36 isolates (100%) examined in the study were multi-drug resistant (MDR) i.e., resistant to more than two antibiotics and showed Multiple antibiotic resistance (MAR) index ranging from 0.40-0.50 (Table 3)
Summary
Non-typhoidal Salmonellae (NTS) has emerged as a major group of foodborne pathogens which causes gastroenteritis, septicaemia, endocarditis and subsequent infections like intra-abdominal infections, and pulmonary infections[1]. Salmonellosis can occur or spread by consumption of contaminated foods of animal origin, such as those from poultry, fish, eggs, beef and dairy products[3]. Both the developed and developing countries have recently reported continuous increase in the incidence of human salmonellosis in patients who are immunosuppressed, or at the extremes of age[4]. Recommended regimens for the treatment for salmonellosis include the traditional firstline drugs like ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole[5]. Quinolone and third-generation cephalosporin antibiotics are preferred for the treatment against salmonellosis[5]
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