Ehime Prefectural University of Health Sciences, Tobecho, Iyogun, Ehime, Japan.
J Infect Chemother. 2010 Jun;16(3):170-3. doi: 10.1007/s10156-010-0037-9. Epub 2010 Feb 27.
The detection of biofilm-producing (ica AB) and methicillin resistance genes (mec A) was investigated in 70 blood culture isolates of Staphylococcus epidermidis and in 66 and 51 isolates from human hands and the vestibules of the nose, respectively, of 77 healthy subjects who gave consent. Of the 70 strains isolated from blood culture testing, both ica AB and mec A were detected in 36 (51.4%), and neither was detected in 4 (5.7%). The mec A gene only was detected in 30 (42.9%), but no isolate from blood culture testing possessed the ica AB gene alone. In contrast, of the 66 isolates from healthy hands, only one isolate (1.5%) possessed both genes, whereas neither was detected in 56 (84.8%), but the mec A gene was detected in 9 (13.6%). Of the 51 isolates from the nasal vestibules, both genes were detected in 12 (23.5%), and neither in 15 (29.4%). Moreover, the mec A gene was detected in 17 (33.3%). Thus, S. epidermidis strains that normally inhabit the nasal vestibule were found to carry the ica AB and mec A genes more frequently than those that inhabit the fingers. The ica AB and mec A genes were detected in S. epidermidis isolated in blood culture tests from patients diagnosed with sepsis associated with catheter-related bloodstream infection (CR-BSI). Both genes were detected in 7 (70.0%) of 10 isolates, and the mec A gene alone was detected in 3 (30.0%). In fact, we could not detect any strain carrying only the ica AB gene from S. epidermidis, an infecting organism of CR-BSI. This suggests that surviving strains carrying the mec A gene cause severe infection on empirical administration of an antibacterial drug, although biofilm formation by the ica AB gene is also important for CR-BSI. Based on these findings, most strains of S. epidermidis causing CR-BSI are biofilm-producing beta-lactam-resistant (methicillin-resistant) bacteria. When S. epidermidis is isolated from blood culture testing, the identification of both ica AB and mec A genes may be significant with regard to judging whether the detected strain is the etiologic agent of CR-BSI.
在 77 名同意参与的健康受试者中，我们分别从他们的手部和鼻腔前庭中分离出 66 株和 51 株表皮葡萄球菌，并对其生物膜产生（ica AB）和耐甲氧西林基因（mec A）进行了检测。在 70 株从血液培养检测中分离出的菌株中，36 株（51.4%）同时检测到了 ica AB 和 mec A，4 株（5.7%）未检测到。仅检测到 mec A 基因的有 30 株（42.9%），但没有一株单独携带 ica AB 基因。相比之下，在 66 株来自健康手部的分离株中，只有 1 株（1.5%）同时携带这两个基因，而在 56 株（84.8%）中未检测到，而 mec A 基因则在 9 株（13.6%）中检测到。在 51 株来自鼻腔前庭的分离株中，12 株（23.5%）同时携带这两个基因，而在 15 株（29.4%）中未检测到。此外，mec A 基因在 17 株（33.3%）中被检测到。因此，与手指相比，正常定植于鼻腔前庭的表皮葡萄球菌分离株携带 ica AB 和 mec A 基因的频率更高。在诊断为与导管相关血流感染（CR-BSI）相关的败血症的患者的血液培养试验中分离出的表皮葡萄球菌中，检测到了 ica AB 和 mec A 基因。在 10 株分离株中，有 7 株（70.0%）同时检测到了这两个基因，而 3 株（30.0%）仅检测到 mec A 基因。事实上，我们无法从导致 CR-BSI 的感染菌表皮葡萄球菌中检测到仅携带 ica AB 基因的任何菌株。这表明，尽管 ica AB 基因的生物膜形成对 CR-BSI 也很重要，但携带 mec A 基因的存活菌株会导致严重的感染，在经验性给予抗菌药物治疗时。基于这些发现，引起 CR-BSI 的大多数表皮葡萄球菌分离株是产生物膜的耐β-内酰胺（耐甲氧西林）细菌。当从血液培养检测中分离出表皮葡萄球菌时，同时鉴定 ica AB 和 mec A 基因可能对判断检测到的菌株是否为 CR-BSI 的病原体具有重要意义。
