Background: An increasing pattern of fluoroquinolone resistance (FQR) among bacterial pathogens has been described worldwide. In this study, we compared the patterns of genetic mechanisms that confer FQR for Escherichia coli and Klebsiella pneumoniae isolated from the Assiut University Hospitals in Egypt.
Methods: Eighty-seven clinical E. coli and K. pneumoniae isolates were tested for mutations in gyrA, gyrB, parC, and parE genes by polymerase chain reaction (PCR) amplification and DNA sequencing. The presence of plasmid-mediated quinolone resistance (PMQR) genes qnrA, qnrB, qnrS, aac(6¢)-Ib, qepA was screened by PCR and characterized by conjugation. Correlations between different FQR mechanisms and ciprofloxacin minimal inhibitory concentration (MIC) levels were determined.
Results: A higher number of quinolone resistance-determining region (QRDR) mutations was detected in
E. coli, while the number of PMQR determinants was significantly higher in K. pneumoniae. However,
K. pneumoniae showed stronger correlations than E. coli between MIC levels and number of mutations in the QRDR per isolate (rs = 0.8, p < 0.0001 and rs = 0.7, p < 0.0001, respectively) as well as between MIC levels and number of plasmids (rs = 0.4, p = 0.005 and rs = 0.3, p = 0.02, respectively).
Conclusions: Although we observed a prevalence of chromosomal mutations for E. coli and the presence of plasmid-encoded genes for K. pneumoniae that resulted in FQR phenotype, high levels of FQR appeared to occur as a result of gradual accumulation of mutations in QRDR for both bacteria. To our best of knowledge, this is the first study to report and compare the correlation between FQ MIC levels and different genetic mechanisms for FQR in Enterobacteriaceae.