特地唑胺对利奈唑胺不敏感革兰阳性球菌的体外抗菌活性研究

In vitro antibacterial activity of tedizolid against linezolid-resistant Gram-positive cocci

目的检测利奈唑胺不敏感革兰阳性球菌对新型噁唑烷酮类抗菌药物特地唑胺的敏感性,并探讨特地唑胺不敏感菌株的耐药机制。方法收集临床分离非重复革兰阳性球菌170株,包括利奈唑胺耐药头状葡萄球菌46株、利奈唑胺敏感头状葡萄球菌19株、利奈唑胺不敏感肠球菌55株、利奈唑胺敏感肠球菌12株、甲氧西林耐药金黄色葡萄球菌19株、甲氧西林敏感金黄色葡萄球菌18株、利奈唑胺耐药金黄色葡萄球菌1株。采用微量肉汤稀释法检测所有菌株对特地唑胺和利奈唑胺的最小抑菌浓度(MIC),并比较两种药物的抗菌活性。采用PCR结合Sanger测序技术分析特地唑胺不敏感革兰阳性球菌cfr、optrA基因携带情况及23S rRNA V区突变。结果利奈唑胺耐药头状葡萄球菌(MIC_(90)>256μg/mL)对特地唑胺的MIC值为4~32μg/mL;利奈唑胺不敏感肠球菌(MIC值4~16μg/mL)中,特地唑胺的敏感率为10.9%,其MIC值为0.5~2μg/mL;1株利奈唑胺耐药金黄色葡萄球菌对特地唑胺敏感,MIC值为0.5μg/mL。特地唑胺对利奈唑胺敏感的金黄色葡萄球菌和肠球菌的MIC值均为0.5μg/mL,对利奈唑胺敏感头状葡萄球菌的MIC值为0.125μg/mL。耐药基因分析显示,特地唑胺耐药头状葡萄球菌cfr基因携带率为87.0%(40/46),23S rRNA V区G2576T的突变率为100%;特地唑胺不敏感肠球菌optrA基因携带率为85.7%(42/49),显著高于特地唑胺敏感株的22.2%(P<0.001);1株利奈唑胺耐药特地唑胺敏感的金黄色葡萄球菌携带cfr基因。结论对于利奈唑胺不敏感的革兰阳性球菌,特地唑胺的抗菌活性是利奈唑胺的8~32倍,其耐药机制可能与携带optrA基因及23S rRNA V区G2576T突变有关。

Objective To investigate the susceptibilities of linezolid-resistant Gram-positive cocci to tedizolid,a novel oxazolidinone antibiotic,and the drug resistance mechanism of tedizolid-resistant isolates.Methods A total of 170 clinical isolates of non-repetitive Gram-positive cocci were collected,including 46 linezolid-resistant Staphylococcus capitis(LRSC),19 linezolid-susceptible Staphylococcus capitis(LSSC),55 linezolid-resistant Enterococcus(LRE),12 linezolid-susceptible Enterococcus(LSE),19 methicillin-resistant Staphylococcus aureus(MRSA),18 methicillin-susceptible Staphylococcus aureus(MSSA)and 1 linezolid-resistant Staphylococcus aureus(LRSA).The minimal inhibitory concentrations(MIC)of all isolates against tedizolid and linezolid were determined by the broth dilution method,and the antibacterial activities of the two drugs were compared.The resistance genes cfr and optrA and the mutation of 23S RNA V region in the tedizolid-resistant Gram-positive cocci were detected by PCR combined with Sanger sequencing.Results The MIC of tedizolid against LRSC(MIC_(90)>256μg/mL)was 4-32μg/mL.The sensitivity rate and MIC of tedizolid against LRE(MIC for linezolid:4-16μg/mL)were 10.9%and 0.5-2μg/mL,respectively.One strain of LRSA was sensitive to tedizolid,and its MIC was 0.5μg/mL.The MICs of tedizolid against LSE and LSSC were 0.5μg/mL and 0.125μg/mL,respectively.Analysis of resistance genes showed that the carrying rate of cfr gene in tedizolid-resistant Staphylococcus capitis was 87.0%(40/46),and that the mutation rate of G2576T in 23S rRNA V region was 100%.The carrying rate of optrA gene in tedizolid-resistant Enterococci was 85.7%(42/49),which was significantly higher than that in tedizolid-susceptible strains(22.2%,P<0.001).One linezolid-resistant and tedizolid-susceptible Staphylococcus aureus strain carried the cfr gene.Conclusion The antibacterial activity of tedizolid against linezolid-resistant Gram-positive cocci is 8-32 times that of linezolid,and its resistance mechanism may be related to carrying optrA gene and G2576T mutation in 23S rRNA V region.