Revisit of Fluoroquinolone and Azithromycin susceptibility breakpoints for Salmonella enterica serovar Typhi.

In this study, the inhibition zone diameters and MICs of nalidixic acid, ciprofloxacin, ofloxacin, levofloxacin and azithromycin were determined in S. Typhi Kolkata isolates (n=146) for 16 years period (1998 to 2013) and the data was compared with the available CLSI breakpoints. Very major error (VME) and major error (ME) of FQs were not observed in the study isolates, but the minor error (mE) of ciprofloxacin (15.8%) and ME of azithromycin (3.5%) exceeded the acceptable limit. A positive correlation between MICs of FQ and mutations in quinolone resistance-determining region (QRDR) showed reliability of MIC results to determine FQ susceptibility of S. Typhi (n=74). Isolates showing decreased ciprofloxacin susceptibility (MIC 0.125-0.5µg/ml) were likely to have at least one mutation in the QRDR region. The results on DD breakpoints of ofloxacin (resistant, ≤15mm; intermediate, 16 to 24mm and susceptible, ≥25mm) and levofloxacin (resistant, ≤18mm; intermediate, 19 to 27mm and susceptible, ≥28mm) corroborated with earlier studies. In view of the emerging FQs and azithromycin resistant S. Typhi isolates, DD and MIC breakpoints of those antimicrobials should be revisited routinely. PMID: 27221661 [PubMed - as supplied by publisher]
Source: Journal of Medical Microbiology - Category: Microbiology Authors: Tags: J Med Microbiol Source Type: research