Six‑year susceptibility trends and effect of revised Clinical Laboratory Standards Institute breakpoints on ciprofloxacin susceptibility reporting in typhoidal Salmonellae in a tertiary care paediatric hospital in Northern India.

ABSTRACT

The antimicrobial trends over 6 years were studied, and the effect of revised Clinical Laboratory Standards Institute (CLSI) breakpoints (2012) for ciprofloxacin susceptibility reporting in typhoidal Salmonellae was determined. A total of 874 (95.4%) isolates were nalidixic acid‑resistant (NAR). Using the CLSI 2011 guidelines (M100‑S21), 585 (66.9%) isolates were ciprofloxacin susceptible. The susceptibility reduced to 11 (1.25%) isolates when interpreted using 2012 guidelines (M100‑S22). Among the forty nalidixic acid susceptible (NAS) Salmonellae, susceptibility to ciprofloxacin decreased from 37 isolates (M100‑S21) to 12 isolates (M100‑S22). The 25 cases which appeared resistant with newer guidelines had a minimum inhibitory concentration (MIC) range between 0.125 and 0.5 μg/ml. MIC50 for the third generation cephalosporins varied between 0.125 and 0.5 μg/ml over 6 years whereas MIC90 varied with a broader range of 0.19–1 μg/ml. The gap between NAR and ciprofloxacin‑resistant strains identified using 2011 guidelines has been reduced; however, it remains to be seen whether additional NAS, ciprofloxacin‑resistant isolates are truly resistant to ciprofloxacin by other mechanisms of resistance.