Antibiotic sensitivity pattern of Salmonella enterica serovar Typhi with special reference to nalidixic acid

Abstract

Introduction: Recently, Salmonella Typhi resistance to many of the commonly used antibiotics like chloramphenicol, amoxicillin and cotrimoxazole, has posed a challenge to treat enteric fever. Minimum inhibitory concentration (MIC) of ciprofloxacin is increasing which is responsible for both treatment failure and causing serious complications. Resistance to nalidixic acid can be used as an indirect indicator to detect increased ciprofloxacin MIC. Hence, study was conducted to know the antibiotic sensitivity pattern of Salmonella enterica serovar Typhi with special reference to nalidixic acid resistance. Materials and Methods: A retrospective study of S. Typhi isolates was conducted. 106 blood samples from patients of all age group who were clinically suspected of enteric fever were included. Blood culture was done and S. Typhi isolates were identified and tested for susceptibility to ampicillin, chloramphenicol, cotrimoxazole, ciprofloxacin, ceftriaxone and nalidixic acid by disc diffusion method. Result: 22(20.8%) S. Typhi isolates were isolated from 106 blood samples. Chloramphenicol showed 100% sensitivity. Susceptibility to ampicillin (81.8%), cotrimoxazole (81.8%) and ceftriaxone (90.9%) was high and to ciprofloxacin (72.7%) and nalidixic acid (45.5%) was low. Conclusion:Ampicillin, chloramphenicol, cotrimoxazole and ceftriaxone showed maximum sensitivity and hence can be used for effective treatment. Nalidixic acid resistance was very high and all these resistant isolates showed decreased sensitivity to ciprofloxacin. Hence nalidixic acid sensitivity can be used for the detection of decreased susceptibility to ciprofloxacin. Keywords: Salmonella Typhi, Ciprofloxacin, Resistance, Nalidixic acid