血培养中表皮葡萄球菌与ica、mecA基因研究

Research on Staphylococcus epidermidis from blood culture and detection of icaand mecAgenes

目的从基因水平探索如何区分血培养中分离的表皮葡萄球菌(SEP)是污染菌或致病菌,为临床医师正确诊断提供科学依据。方法将73株来源于阳性血培养,导管相关性感染(CRBSI)以及从临床健康医护人员手部、鼻黏膜分别检出的12、70、55株SEP,运用法国生物梅里埃公司全自动细菌鉴定仪进行菌株鉴定,PCR法检测icaA、icaB和mecA基因,比较ica基因和mecA基因在不同标本来源中的检出率。结果血培养中同时携带ica和mecA基因占52.0%,同时,94.6%的菌株被检测出mecA基因;CRBSI的12株SEP中,有75.0%同时存在mecA和ica基因;从健康人手部皮肤分离的菌则很少同时具有ica和mecA基因,仅有15.8%的菌株携带mecA;健康人鼻黏膜定植的菌同时具有ica和mecA基因的占21.8%,高于手部皮肤分离率,而ica及mecA基因的携带率分别为60.0%、30.9%,明显高于皮肤定植的SEP。结论血培养中分离到SEP时,通过检测ica和mecA的存在与否对于区分污染菌和致病菌有重要作用。

OBJECTIVE To explore how to distinguish Staphylococcus epidermidis isolated from blood culture is contaminating bacteria or pathogens from the genetic level, so as to provide the scientific evidence for clinically correct diagnosis. METHODS The total S. epidermidis included 73 strains from positive blood cultures, 12 strains from catheter-related infections and 125 strains from clinical health care workers （70 from them hands and 55 from nasal samples）. The automatic micro-identification system （BioMerieux, France） was used to identify the strains. The icaA, icaB and mecA genes were detected by the polymerase-chain-reaction method. The detection rates of ica and mecA genes in different specimen sources were compared. RESULTS The strains from the blood culture carried both the ica and rnecA genes occupied with 52.0%. Meanwhile, 94.6% of the strains were detected rnecA gene. Among the 12 strains of S. epidermidis causing CRBSI, 75. 0% carried both mecA and ica genes. The strains from healthy human hands rarely had both ica and mecA genes. Only 15.8% strains carried mecA. 21.8% of the strains from healthy human nasal had both ica and mecA genes, the separation rate was higher than that from the hands. The carrying rates of ica and mecA gene were 60. 0% and 30. 9%, respectively, significantly higher than those from the hands. CONCLUSION The detection of the presence of the ica and rnecA plays an important role in distinguishing contaminating bacteria and pathogens when the S. epidermidis is isolated from blood culture.