Studies on virulence, antimicrobial resistance and genetic diversity of Salmonella typhimurium isolates from North india
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Date
2016-08
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Salmonellosis is one of the most frequently reported food-borne diseases world-wide commonly caused by Salmonella Typhimurium and Salmonella Enteritidis serovars. The present study was undertaken to understand the pathogenic nature, antimicrobial resistance pattern and heterogeneity of S. Typhimurium isolates (n=94) of diverse origin from northern states of India (Uttar Pradesh, Uttarakhand, Bihar, Assam and Jammu & Kashmir). All the 94 isolates were confirmed to be S. Typhimurium through various morphological, biochemical, serological and molecular methods. Salmonella Typhimurium isolates revealed varying distribution pattern of virulence viz., invA (100 %), sipA (100 %), sopE1 (61.7%), fliC (80.85%), mgtC (100 %), spvC (12.76%). stn (89.36%), sopB (94.68%) and gipA (45.74%). The presence of virulence determinants located on prophages (sopE1 and gipA) and plasmids (spvC) of S. Typhimurium isolates from North India was found to be less compared to the presence of virulence genes located on SPIs (invA, sipA, fliC, mgtC, stn and sopB). Antimicrobial susceptibility testing revealed higher resistance against nalidixic acid and sulfafurazole (28.72% each) followed by tetracycline (14.89%), ampicillin and ciprofloxacin (12.76% each), levofloxacin and norfloxacin (11.7% each). This appears to be the first study to report the emergence of S. Typhimurium isolates (animal origin) resistant to third generation fluroquinolones in Patna (Bihar) and Pantnagar (Uttarakhand). The findings also suggest the presence of MDR strains of S. Typhimurium in northern states of India except Assam. The present study also detected various antimicrobial resistance genes corresponding to the respective antibiotic classes viz., blaTEM, strA, strB, tet(A), sul1 and sul2 along with class 1 integron. The class 1 integron were identified with two type of gene cassette viz., dfrA5 and aac(3-Id)-aadA7 0.4 kb and 1.3 kb size, respectively. Genetic diversity analysis performed by ERIC-PCR revealed a discriminative index of 0.7817 while, one of the isolates (S145) from Guwahati (Assam) was found untypable. The PFGE analysis of 16 isolates revealed a discriminatory power of 0.9 and it was proved to be the more efficient tool in comparison to ERIC-PCR. The genetic similarity among the isolate from different sources and locations indicate their common origin.
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