A study of antibiogram of Salmonella enterica serovar Typhi isolates from Pondicherry, India.

BACKGROUND: Enteric fever caused by Salmonella enterica serovar Typhi (S. Typhi) is an important public health problem in developing countries like India.1 The emergence of resistance to fluoroquinolones has reduced the therapeutic options available. Currently, the uniform laboratory interpretation of ciprofloxacin and azithromycin susceptibility remains unclear.

AIMS: To study the antibiogram of S. Typhi isolates with special emphasis on in-vitro activity of ciprofloxacin and azithromycin.

METHOD: We evaluated the antimicrobial susceptibility pattern of 16 S. Typhi isolates from January 2012 to June 2013. We also determined by Epsilometer-test (E-test) method, the minimum inhibitory concentration (MIC) of ciprofloxacin and azithromycin against these isolates and compared them with their corresponding disc diffusion sizes.

RESULTS: Fifteen (93.75 per cent) isolates were sensitive to chloramphenicol, 14 (87.5 per cent) were sensitive to cotrimoxazole. All isolates were resistant to nalidixic acid. MICs for ciprofloxacin ranged from 6μg/ml to 15μg/ml and corresponding zone diameters ranged from 15mm to 26mm. MIC and zone diameters for ciprofloxacin had significant negative correlation. MICs for azithromycin ranged from 3μg/ml to 24μg/ml, corresponding zone diameters ranged from 13mm to 19mm. However, MIC and zone diameters for azithromycin had no significant negative correlation.

CONCLUSION: The widespread emergence of resistance to fluoroquinolones and reappearance of sensitivity to firstline drugs has reinforced the need for antibiotic recycling. There is a need to have uniform laboratory testing guidelines for testing susceptibility to ciprofloxacin and azithromycin for S. Typhi isolates.