苯唑西林敏感、mecA基因阳性的猪源金黄色葡萄球菌的流行、分子分型及耐药性研究

目的] 为了解我国猪源苯唑西林敏感-mecA阳性金黄色葡萄球菌（Oxacillin-susceptible，mecA-positive Staphylococcus aureus，OS-MRSA）的流行情况、菌株分子特征及耐药性，本研究对我国中西部4个省份（甘肃、陕西、河南和广西）的9个规模化养猪场进行鼻腔拭子样本采集。方法] 运用PCR扩增nuc和mecA基因及苯唑西林耐药性检测对OS-MRSA菌株进行分离鉴定。然后对分离所得的OS-MRSA菌株进行26种毒素编码基因、16种抗生素耐药性以及spa、MLST和SCCmec分型检测。结果] 结果表明，采集的884份样本中，67份样本7.6%（67/884）分离到金黄色葡萄球菌，包括50株甲氧西林敏感菌株（Methicillin-sensitive Staphylococcus aureus，MSSA）、8株苯唑西林耐受-mecA阳性金黄色葡萄球菌（Oxacillin-resistant mecA-positive，OR-MRSA）和9株OS-MRSA菌株。26种被检毒素编码基因中有9种毒素编码基因被检出，其中hla基因检出率最高，其次为hld、hlb、hlg、sei、sem、seg、sen和seo。此外，67株分离株中仅有16株携带肠毒素编码基因，其中OR-MRSA和OS-MRSA菌株分别占37.5%（6/16）和50.0%（8/16），且携带毒素编码基因的菌株克隆型均为ST9-t899。16种所测试抗生素中，菌株对12种抗生素表现为耐药，其中MSSA、OR-MRSA和OS-MRSA分离株分别主要对1-8、10-12和7-11种抗生素耐药。所有分离株共有4种克隆型ST398-t571、ST9-t899、ST398-t034和t11241，其中ST9-t899为MRSA菌株唯一克隆型和ST398-t571为MSSA优势克隆型。除4株分离株未检测到SCCmec分型外，IV_b（76.5%，13/17）是MRSA分离株的唯一分型。结论] 结果表明，我国猪源MRSA分离株对苯唑西林药物敏感性发生了改变，出现了较多的苯唑西林敏感菌株。此外，MSSA和MRSA分离株优势克隆型分别为ST398-t571和ST9-IVb-t899。研究还发现，克隆型与毒素编码基因有显著相关性，携带毒素编码基因的菌株克隆型均为ST9-t899。通过了解我国猪源MSSA、OR-MRSA和OS-MRSA的流行、分子特征和耐药性，可以为我国猪源金黄色葡萄球菌的防控提供数据支持。

Molecular typing and antimicrobial susceptibility of oxacillin-susceptible, mecA-positive Staphylococcus aureus from pigs

Objective] To investigate the prevalence, molecular characteristics and antibiotic resistance of oxacillin-susceptible, mecA-positive Staphylococcus aureus (OS-MRSA) isolates from pigs, we collected samples from 9 large-scale pig farms in four central and western provinces of China (Gansu, Shaanxi, Henan and Guangxi). Methods] The OS-MRSA isolates were identified by amplifying nuc and mecA gene and oxacillin susceptibility tests. Twenty-six toxin-encoding genes, 16 kinds of commonly used antibiotic resistance and molecular typing (spa, MLST and SCCmec) of the isolates were detected.Results] The results showed that 67 (7.6%, 67/884) of the 884 samples were contaminated with S. aureus. A total of 67 isolates were isolated, including 50 isolates of methicillin-susceptible Staphylococcus aureus (MSSA), 8 isolates of oxacillin-resistant mecA-positive (OR-MRSA) and 9 isolates of OS-MRSA. Among the 26 toxin-encoding genes, 9 toxin-encoding genes were detected, and the hla gene had the highest detection rate, followed by hld, hlb, hlg, sei, sem, seg, sen and seo. Sixteen isolates that carrying the enterotoxin-encoding genes, OR-MRSA and OS-MRSA isolates accounted for 37.5% (6/16) and 50.0% (8/16), respectively. The isolates carrying the enterotoxin-encoding genes were all ST9-t899 clone type. Among the 16 antibiotics tested, the isolates were resistant to 12 antibiotics, among which MSSA, OR-MRSA and OS-MRSA isolates were mainly resistant to 1-8, 10-12 and 7-11 antibacterial drugs, respectively. Four clone types (ST398-t571, ST9-t899, ST398-t034 and t11241) were identified, among which ST9-t899 was the only clone type of MRSA and ST398-t571 was the dominant clone type of MSSA. With the exception of four isolates where SCCmec typing was not detected, IV_b (76.5%, 13/17) was the only type in MRSA isolates. Conclusion] To sum up, the sensitivity of pig MRSA isolates to oxacillin had changed, and they were generally sensitive to oxacillin. In addition, the dominant clone types of MSSA and MRSA strains were ST398-t571 and ST9-t899, respectively. The study also found that the clone type is significantly related to the toxin genes carrying status, and the clone type of the strain carrying the toxin genes was ST9-t899. Therefore, understanding the prevalence, molecular characteristics and drug resistance of MSSA and OS-MRSA from pigs in China can provide data support for the prevention and control of Staphylococcus aureus infection for pigs.