Resumen

Introduction: Considering the limitations of screening with nalidixic acid to detect reduced susceptibility to fluoroquinolones of Salmonella enterica serovar Typhi (S.Typhi) strains, we evaluated the use of a 30 ìg nalidixic acid disc screening method in Pakistan. Methodology: Non duplicate nalidixic acid susceptible S. Typhi isolates (246) from 2003-2008 were retrieved from the Salmonella strain bank. Minimum inhibitory concentrations of ciprofloxacin for all strains were determined by agar dilution and further rechecked by ciprofloxacin E-tests. E. coli ATCC 25922 was used as the control strain. The MIC data for ciprofloxacin were compared with nalidixic acid disk (30ìg) zone diameters. Results: Repeat testing of all S. Typhi isolates with a nalidixic acid (30ìg) disk showed 100% susceptibility with an average zone diameter of 26 mm. Agar dilution testing revealed reduced susceptibility to ciprofloxacin, with MICs of 0.125 ìg /ml for three (1.2%) isolates only. Zone sizes of strains with higher MICs were significantly lower than the strains with lower MICs (20 versus 26 mm) (p value <0.001). Conclusion: Estimation of fluoroquinolone MICs on every nalidixic acid susceptible S. Typhi strain is not cost effective in our setting; the proportion of strains with high fluoroquinolone MICs was found to be very low. We recommend periodic fluoroquinolone MIC determination to include all isolates with a nalidixic acid borderline zone (size 20-22 mm).

Palabras clave: Enteric fever; antimicrobial resistance; nalidixic acid susceptible; fluoroquinolone resistant.

2013-01-17   |   331 visitas   |   Evalua este artículo 0 valoraciones

Vol. 6 Núm.10. Octubre 2012 Pags. 700-703 J Infect Developing Countries 2012; 6(10)