Lei Y, Gui X, Feng G
The Second Affiliated Hospital, Hubei Medical University, Wuhan 430071, China.
Zhonghua Nei Ke Za Zhi. 2001 Mar;40(3):176-9.
To investigate the resistance of Staphylococcus aureus(SA) and the mechanisms of its resistance to fluoroquinolones (FQ).
The susceptibility of SA (200 strains) to 12 antibiotics was detected by disc diffusion, The minimal inhibitory concentrations (MICs) of 52 strains to three FQ were determined by agar dilution method. 52 strains resistant to ciprofloxacin (MIC> or =4 mg/L) were studied for the presence of point mutations in the gyrA gene and grlA gene by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method and for the expression of norA gene by reserpine reverse test respectively.
34% of the strains were resistant to oxacillin(methicillin resistant Staphylococcus aureus, MRSA) and other antimicrobials as well, but no vancomycin resistant strain was found. The resistance rate of MRSA to ciprofloxacin was 79.4% and cross-resistance existed. It was found that 42 strains (80.8%) had a mutation at gyrA codon 84 (TCA-->TTA or GCA). Mutations at grlA codon 80 (TCC-->TAC or TTC) and codon 84 (GAA-->AAA)were observed in 10 (19.2%) and 14 strains(26.9%) respectively.Strains containing mutations in gyrA or both gyrA and grlA gene showed a higher level of ciprofloxacin resistance than those with alternation in grlA gene but with wild type gyrA or non-gyrA mutants (P < 0.01). Decreased MICs to ciprofloxacin, norfloxacin and levofloxacin in reserpine reverse test indicated the presence of norA phenotype.
It is clear that emergence of resistant SA strains will continue to be a problem, especially in MRSA which was resistant to most of the antibiotics. Fluoroquinolones are not the choice for MRSA now. The resistance to fluoroquinolones in clinical isolates of SA are due to the mutations of the gyrA and grlA gene encoding the target enzyme of fluoroquinolones and cell membrane resistance. Mutations of grlA gene may differ in different districts.
研究金黄色葡萄球菌（SA）的耐药性及其对氟喹诺酮类（FQ）耐药的机制。
采用纸片扩散法检测200株SA对12种抗生素的敏感性，用琼脂稀释法测定52株SA对3种FQ的最低抑菌浓度（MIC）。采用聚合酶链反应-限制性片段长度多态性（PCR-RFLP）方法研究52株对环丙沙星耐药（MIC≥4mg/L）菌株的gyrA基因和grlA基因点突变情况，并用利血平反向试验分别检测norA基因的表达。
34%的菌株对苯唑西林耐药（耐甲氧西林金黄色葡萄球菌，MRSA），且对其他抗菌药物也耐药，但未发现耐万古霉素菌株。MRSA对环丙沙星的耐药率为79.4%，存在交叉耐药。发现42株（80.8%）在gyrA基因84密码子（TCA→TTA或GCA）处有突变。分别在10株（19.2%）和14株（26.9%）中观察到grlA基因80密码子（TCC→TAC或TTC）和84密码子（GAA→AAA）处的突变。与gyrA基因野生型或非gyrA基因突变但grlA基因有改变的菌株相比，gyrA基因或gyrA和grlA基因均有突变的菌株对环丙沙星的耐药水平更高（P<0.01）。利血平反向试验中环丙沙星、诺氟沙星和左氧氟沙星的MIC降低表明存在norA表型。
显然，耐药SA菌株的出现仍将是一个问题，尤其是对大多数抗生素耐药的MRSA。目前氟喹诺酮类药物不是MRSA的治疗选择。SA临床分离株对氟喹诺酮类药物的耐药性是由于编码氟喹诺酮类药物靶酶的gyrA和grlA基因的突变以及细胞膜耐药性。grlA基因的突变在不同地区可能有所不同。
