Pletz M W R, McGee L, Van Beneden C A, Petit S, Bardsley M, Barlow M, Klugman K P
Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA.
Antimicrob Agents Chemother. 2006 Mar;50(3):943-8. doi: 10.1128/AAC.50.3.943-948.2006.
Fluoroquinolone resistance in Streptococcus pyogenes has been described only anecdotally. In this study we describe two invasive ciprofloxacin-resistant S. pyogenes isolates (ciprofloxacin MICs, 8 mg/liter), one of which shows evidence of interspecies recombination. The quinolone resistance-determining regions of gyrA and parC were sequenced. In both isolates, there was no evidence for an efflux pump and no mutation in gyrA. Both isolates had an S79F mutation in parC that is known to confer fluoroquinolone resistance. In addition, a D91N mutation in parC, which is not related to fluoroquinolone resistance but is a feature of the parC sequence of Streptococcus dysgalactiae, was found in one isolate. The parC nucleotide sequence of that isolate showed greater diversity than that of S. pyogenes. A GenBank search and phylogenetic analysis suggest that this isolate acquired resistance by horizontal gene transfer from S. dysgalactiae. Statistical testing for recombination confirmed interspecies recombination of a 90-bp sequence containing the S79F mutation from S. dysgalactiae. For the other isolate, we could confirm that it acquired resistance by spontaneous mutation by identifying the susceptible ancestor in an outbreak setting.
化脓性链球菌对氟喹诺酮类药物耐药的情况仅有零星报道。在本研究中，我们描述了两株对环丙沙星耐药的侵袭性化脓性链球菌分离株（环丙沙星 MIC 为 8 mg/L），其中一株显示存在种间重组的证据。对 gyrA 和 parC 的喹诺酮耐药决定区进行了测序。在这两株分离株中，均未发现存在外排泵的证据，且 gyrA 未发生突变。两株分离株的 parC 均有 S79F 突变，已知该突变可导致对氟喹诺酮类药物耐药。此外，在其中一株分离株中发现 parC 存在 D91N 突变，该突变与氟喹诺酮耐药无关，但却是停乳链球菌 parC 序列的一个特征。该分离株的 parC 核苷酸序列显示出比化脓性链球菌更高的多样性。GenBank 搜索和系统发育分析表明，该分离株通过水平基因转移从停乳链球菌获得耐药性。重组的统计检验证实了包含来自停乳链球菌 S79F 突变的 90 bp 序列发生了种间重组。对于另一株分离株，我们通过在一次暴发疫情中鉴定出易感祖先，从而证实它是通过自发突变获得耐药性的。
