一株甲氧西林敏感mecA基因阳性金黄色葡萄球菌的鉴定及生物学特性研究

Identification and biological characteristics study of an oxacillin-susceptible mecA-positive Staphylococcus aureus strain

中文关键词:  OS-MRSA  ST59-t437  mecA基因沉默  毒力特征

英文关键词:oxacillin-susceptible mecA-positive Staphylococcus aureus  mecA gene silencing  virulence profile

中文摘要:

      目的 对一株分离自零售鸡肉样本、表型为甲氧西林敏感但携带mecA基因的金黄色葡萄球菌(oxacillin-susceptible mecA-positive Staphylococcus aureus, OS-MRSA)进行全面的生物学特性分析, 评估其毒力潜能及分子分型特征。方法 从超市冷冻整鸡样本中分离金黄色葡萄球菌SAC10, 通过基质辅助激光解吸电离飞行时间质谱法(matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, MALDI-TOF MS)进行鉴定, 并采用药敏实验和聚合酶链式反应(polymerase chain reaction, PCR)检测耐药性和mecA基因。利用全基因组测序分析其耐药基因、毒力基因及分子分型。通过溶血实验、生物被膜形成实验和大蜡螟感染模型评估其毒力表型。采用序列比对分析mecA基因的调控机制。结果 SAC10为ST59-t437-IVa(2B)型OS-MRSA, 携带mecA但表型敏感, 所携带的耐药基因和耐药谱一致。其基因组携带多种毒力因子(hlgABC、seb、sek、seq、aur、sak、scn), 表现出强溶血活性和生物被膜形成能力。大蜡螟实验显示中等毒力(72 h存活率16.67%)。mecA基因上游启动子区域插入ISSau3抑制mecA表达, 从而呈现敏感表型。结论 SAC10作为食源性OS-MRSA, 兼具毒力与隐蔽性耐药基因, 可能通过食物链传播构成潜在健康风险。mecA基因的插入突变导致表型-基因型不一致现象, 提示常规药敏实验需结合分子检测以避免漏检。为食源性OS-MRSA的监测和风险评估提供科学依据。

英文摘要:

      Objective To conduct a comprehensive biological characterization of an oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) strain isolated from a retail chicken sample, assess its virulence potential and molecular typing characteristics. Methods Staphylococcus aureus strain SAC10 was isolated from supermarket frozen whole-chicken samples. Identification was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and antibiotic resistance profiles and the mecA gene were detected by antibiotic susceptibility testing and polymerase chain reaction (PCR). Whole-genome sequencing analyzed resistance genes, virulence genes and molecular typing. Virulence phenotypes were assessed via hemolysis assays, biofilm formation assays, and Galleria mellonella infection models. Sequence alignment elucidated the regulatory mechanism of the mecA gene. Results SAC10 was identified as ST59-t437-IVa(2B) OS-MRSA. It carried mecA but exhibited phenotypic susceptibility, with its resistance gene profile consistent with the antimicrobial susceptibility pattern. The genome harbored multiple virulence factors (hlgABC, seb, sek, seq, aur, sak, scn), demonstrating strong hemolytic activity and biofilm-forming capability. Galleria mellonella assays revealed moderate virulence (16.67% survival at 72 h). Insertion of ISSau3 into the upstream promoter region of mecA suppressed its expression, resulting in the susceptible phenotype. Conclusion As a foodborne OS-MRSA, SAC10 combines virulence with concealed resistance genes, posing potential health risks via the food chain. The insertion mutation in mecA causing genotype-phenotype discordance highlights the need to combine conventional susceptibility testing with molecular detection to prevent underdiagnosis. These findings provide a scientific basis for improved monitoring and risk assessment of foodborne OS-MRSA.