High frequency of non-susceptibility to ciprofloxacin in nontyphoid Salmonella recovered from Brazilian broiler chicken

Abstract

ABSTRACT 1. This study evaluated the minimal inhibitory concentration (MIC) of ciprofloxacin and the presence of plasmid-mediated quinolone resistance (PMQR) mechanisms in 97 nontyphoidal Salmonella spp. isolated from broilers and carcases from three different regions in Brazil. The presence of mutations in quinolone resistance determination regions (QRDRS) was investigated in the ciprofloxacin-resistant strain by DNA sequencing. 2. Most of the Salmonella spp. (85.6%) had intermediate resistance to ciprofloxacin and only one isolate was resistant. MIC breakpoints ranged from ≤0.03 to 1 µg/ml and 67.0% of the strains had a MIC of 0.25 µg/ml (n=65). Thirteen strains (13.4%) were susceptible to ciprofloxacin with MIC ≤0.06 µg/ml. The qnrB gene was detected in eight isolates with intermediate resistance and in two susceptible strains. The other PMQR genes, qnrA, qnrC, qnrD, qnrS, qnrVC, aac(6′)-Ib, qepA, oqxAB and mutations in QRDR were not detected in any strain. 3. There was a high frequency of ciprofloxacin intermediate resistant Salmonella from broiler and broiler carcases from Brazil. The presence of these strains in poultry and derived products poses a risk to public health.