Fluroquinolone resistance in typhoidal Salmonella and its detection by nalidixic acid disc diffusion.

OBJECTIVE To determine the presence of fluoroquinolone resistance in Typhoidal salmonellae at Rawalpindi and the role of nalidixic acid in predicting the resistance against fluoroquinolones in Microbiology Laboratory, Department of Pathology, Army Medical College, Rawalpindi. METHODS One hundred consecutive clinical isolates of Typhoidal salmonellae isolated from blood culture samples were studied. The organisms were identified biochemically and serologically by standard technique. Sensitivity testing was carried out against nalidixic acid and ciprofloxacin by modified Kirby bauer disc diffusion method and minimum inhibitory concentration (MICs) were determined by E-test. RESULTS Seventeen percent of the isolates were resistant to nalidixic acid. Nalidixic acid disc diffusion and MIC estimation by E-test were 100% comparable. All isolates were sensitive to ciprofloxacin but the isolates which were resistant to nalidixic acid had raised MIC values against ciprofloxacin. CONCLUSION Typhoidal salmonellae have not shown an overt in vitro resistance against fluoroquinolones in our set up but a significant population has emerged with raised MIC values. Nalidixic acid susceptibility test can be used an indirect evidence of resistance to quinolones.