Relationship between the Susceptibility of Salmonella.Typhi to Ciprofloxacin, Ofloxacin and their respective Susceptibility To Nalidixic Acid

Background: Typhoid fever is an important cause of morbidity and mortality in many parts of the world including Pakistan. Resistance to the first line anti typhoid drugs viz chloramphenicol, cotrimoxazole and ampicillin has aggravated this situation. Quinolones are currently used as the first line antityphoid drugs, instead. Fluoroquinolones are currently recommended for patients infected with Typhi. The fluoroquinolones have shown good in vitro as well as clinical activity against Typhi infections.Materials and Methods: It was a comparative cross-sectional conducted at Department of Microbiology UHS, Lahore, Pakistan within one year (January 2011-December 2011). A total of 100 clinical isolates of Typhi were evaluated. ATCC 9150 Paratyphi A was used as a standarad strain. The bacterial isolates were preserved in microbanks (Pro-Lab Diagnostics, UK) and stored at-70˚C during a period of (2007- 2011). Data was analysed through SPSS version 22.Results: Of the 100 isolates, 45 strains were showing MIC ≤ 1µg/ml which means that they were susceptible while 55 strains were intermediate having MIC 2µg/ml. No strain was however, found resistant to ciprofloxacin according as per the CLSI 2011. As per the CLSI 2012 revised ciprofloxacin break points for disc diffusion and MIC for salmonella species. According to CLSI 2012 interpretive criteria, on disk diffusion testing 13 isolates were sensitive, 13 were resistant and 74 were intermediate to ciprofloxacin. On MIC, 55 strains were resistant showing MIC ≥1µg/ml and 45 isolates were intermediate showing MIC 0.125-0.5µg/ml. No isolate was found sensitive to ciprofloxacin according to CLSI 2012 interpretive criteria.Conclusion: In conclusion, the present study showed the value of nalidixic acid susceptibility as an indirect but a certain marker of ciprofloxacin susceptibility. Nalidixic acid resistant showed increased minimum inhibitory concentration (MIC) by agar dilution method.