Emergence of fluoroquinolone resistance and possible mechanisms in clinical isolates of Stenotrophomonas maltophilia from Iran

Stenotrophomonas maltophilia exhibits wide spectrum of fluoroquinolone resistance using different mechanisms as multidrug efflux pumps and Sm qnr alleles. Here, the role of smeDEF , smeVWX efflux genes and contribution of Sm qnr alleles in the development of fluoroquinolone resistance was assessed. Ciprofloxacin, levofloxacin and moxifloxacin resistance were found in 10.9%, 3.5%, and 1.6% of isolates, respectively. More than four-fold differences in ciprofloxacin MICs were detected in the presence of reserpine and smeD, F, V expression was significantly associated with ciprofloxacin resistance (p = 0.017 for smeD , 0.003 for smeF , and 0.001 for smeV ). Sm qnr gene was found in 52% of the ciprofloxacin-resistant isolates and Sm qnr8 was the most common allele detected. Fluoroquinolone resistance in S. maltophilia clinical isolates was significantly associated with active efflux pumps. There was no correlation between the Sm qnr alleles and ciprofloxacin resistance; however, contribution of the Sm qnr genes in low-level levofloxacin resistance was revealed.