Frequent topoisomerase IV mutations associated with fluoroquinolone resistance in Ureaplasma species.

This study aimed to investigate the role of quinolone resistance-determining regions (QRDRs) of DNA gyrase (encoded by gyrA and gyrB) and topoisomerase IV (encoded by parC and parE) associated with fluoroquinolone resistance. A total of 114 Ureaplasma spp. strains, isolated from clinical female patients with symptomatic infection, were tested for species distribution and susceptibility to four fluoroquinolones. Moreover, we analysed the QRDRs and compared these with 14 ATCC reference strains of Ureaplasma spp. serovars to identify mutations that caused antimicrobial resistance. Our study indicated that moxifloxacin was the most effective fluoroquinolone against Ureaplasma spp. (MIC range: 0.125-32 μg ml⁻¹). However, extremely high MICs were estimated for ciprofloxacin (MIC range: 1-256 μg ml⁻¹) and ofloxacin (MIC range: 0.5-128 μg ml⁻¹), followed by levofloxacin (MIC range: 0.5-64 μg ml⁻¹). Seven amino acid substitutions were discovered in GyrB, ParC and ParE, but not in GyrA. Ser-83 → Leu/Trp (C248T/G) in ParC and Arg-448 → Lys (G1343A) in ParE, which were potentially responsible for fluoroquinolone resistance, were observed in 89 (77.2 %) and three (2.6 %) strains, respectively. Pro-462 → Ser (C1384T), Asn-481 → Ser (A1442G) and Ala-493 → Val (C1478T) in GyrB and Met-105 → Ile (G315T) in ParC seemed to be neutral polymorphisms, and were observed and occurred along with the amino acid change of Ser-83 → Leu (C248T) in ParC. Interestingly, two novel mutations of ParC and ParE were independently found in four strains. These observations suggest that amino acid mutation in topoisomerase IV appears to be the leading cause of fluoroquinolone resistance, especially the mutation of Ser-83 → Leu (C248T) in ParC. Moxifloxacin had the best activity against strains with Ser-83 → Leu mutation.