Antimicrobial susceptibility of Salmonella enterica serovars in a tertiary care hospital in southern India

BACKGROUND & OBJECTIVES: Salmonella enterica serovars Typhi and Paratyphi are predominantly known to cause enteric fever. Multidrug resistance in S. Tphi and S. Paratyphi has emerged as a cause of concern. This study was done to evaluate status in antimicrobial susceptibility patterns of Salmonella enterica serovar Typhi (S. Typhi) and S. Paratyphi obtained from blood culture in a tertiary care hospital in south India. METHODS: Blood isolates of Salmonella species over a two year period between May 2009 and June 2011 were studied. A total of 322 isolates of Salmonella species were tested for antimicrobial susceptibility by Kirby-Bauer disc diffusion method. The MIC of ciprofloxacin was obtained by E-test, and azithromycin MIC was confirmed by agar dilution method for a limited number of isolates. RESULTS: Of the total of 322 isolates studied, 186 (57.8%) were S. Typhi, 134 (41.6%) were S. Paratyphi A, and two were S. Paratyphi B. Of these, 44(13.66%) were resistant to ciprofloxacin (MIC <0.50 μg/ml) and 296 (91.9%) were nalidixic acid resistant. Of these 296 nalidixic acid resistant isolates, 278 (94%) were susceptible to ciprofloxacin by MIC criteria (<0.5 μg/ml). Of the 262 isolates tested for azithromycin sensitivity, only 120 (46%) were susceptible, whereas 81 (31%) were resistant and 55 (21%) showed intermediate susceptibility. Of the isolates, 322 (90%) were susceptible to ampicillin and (95%) were susceptible to co-trimoxazole. However, all the isolates were susceptible to chloramphenicol and ceftriaxone. INTERPRETATION & CONCLUSIONS: Nalidixic acid resistance screening is not a reliable surrogate indicator of ciprofloxacin resistance. Ciprofloxacin MIC should to be routinely done. Azithromycin resistance appears to be emerging. However, isolates showed a high degree of susceptibility to ampicillin, co-trimoxazole and chloramphenicol. Thus, antibiotics like ampicillin and co-trimoxazole may once again be useful for the management of enteric fever in southern India.