High Level of Resistance to nalidixic acid in Salmonella enterica serovar Typhi in Central India

Background: Fluoroquinolones are the drugs of choice for the treatment of typhoid fever. But the recent increase in minimum inhibitory concentration (MIC) values of ciprofloxacin in Salmonella Typhi may result in delayed response and serious complications. Nalidixic acid resistance has been used as an indirect evidence of increased minimum inhibitory concentration for ciprofloxacin in Salmonella Typhi. Methods: We evaluated the isolates received at the National Salmonella and Escherichia Centre for nalidixic acid and ciprofloxacin susceptibility using standard methods. Minimum inhibitory concentrations have also been evaluated. Results: Ninety-six percent of the isolates were found to be nalidixic acid resistant while all isolates were found to be ciprofloxacin sensitive. The difference between minimum inhibitory concentration values of ciprofloxacin for nalidixic acid resistant and nalidixic acid sensitive isolates was found to be statistically significant. Conclusion: The study may be helpful in revising treatment strategies for the infections caused by nalidixic acid resistant Salmonella Typhi in the country.