Patterns in antimicrobial susceptibility of Salmonellae isolated at a tertiary care hospital in northern India

Abstract

Background & objectives: Multidrug-resistant Salmonellae have emerged worldwide as also in India. The aim of this study was to study the antimicrobial susceptibility pattern of Salmonella enterica serovars isolated at a tertiary care hospital in northern India.

Methods: A total of 106 S. enterica serovars isolated from various clinical samples from January 2011 to June 2012 were tested for antimicrobial susceptibility by Kirby-Bauer disk diffusion method. The minimum inhibitory concentration (MIC) of ciprofloxacin, chloramphenicol and ceftriaxone was determined both by agar dilution method and E-test for all the isolates.

Results: Salmonella Typhi (73.6%) was the predominant isolate followed by S. Paratyphi A (15.1%), S. Typhimurium (9.4%) and S. Enteritidis (1.9%). Of these, 34 (32.1%) were resistant to ciprofloxacin (MIC ≥1 μg/ml by agar dilution) with MIC90 of ciprofloxacin for S. Typhi, S. Paratyphi A and S. Typhimurium being 32, 4 and 1 μg/ml, respectively. All the isolates were sensitive to chloramphenicol (MIC ≤8 μg/ml) and ceftriaxone (MIC ≤1 μg/ml). Disk diffusion method showed high susceptibility rates to cefotaxime (100%), azithromycin (93.4%) and co-trimoxazole (97.2%). Nalidixic acid resistance was seen in 105 (99.1%) isolates. Of the nalidixic acid-resistant strains, only 34 (32.3%) were found to be resistant to ciprofloxacin (MIC ≥1 μg/ml).

Interpretation & conclusions: This study showed an alarming increase in MIC to quinolones and re-emergence of susceptibility to conventional antibiotics among Salmonellae.