葡萄球菌科新 SCCmec 元素的特征。
Characterization of a new SCCmec element in Staphylococcus cohnii.
机构信息
Center of Infectious Diseases, West China Hospital, Sichuan University, Chengdu, China.
出版信息
PLoS One. 2010 Nov 17;5(11):e14016. doi: 10.1371/journal.pone.0014016.
BACKGROUND
Many SCCmec elements of coagulase-negative staphylococci (CoNS) could not be typed using multiplex PCR. Such a 'non-typable' SCCmec was encountered in a Staphylococcus cohnii isolate.
METHODOLOGY/PRINCIPAL FINDINGS: The SCCmec type of methicillin-resistant S. cohnii clinical isolate WC28 could not be assigned using multiplex PCR. Newly-designed primers were used to amplify ccrA and ccrB genes. The whole SCCmec was obtained by three overlapping long-range PCR, targeting regions from left-hand inverted repeat (IRL) to ccrA/B, from ccrA/B to mecA and from mecA to orfX. The region abutting IRL was identified using inverse PCR with self-ligated enzyme-restricted WC28 fragments as the template. WC28 SCCmec had a class A mec gene complex (mecI-mecR1-mecA). The ccrA and ccrB genes were closest (89.7% identity) to ccrA(SHP) of Staphylococcus haemolyticus strain H9 and to ccrB3 (90% identity) of Staphylococcus pseudintermedius strain KM241, respectively. Two new genes potentially encoding AAA-type ATPase were found in J1 region and a ψTn554 transposon was present in J2 region, while J3 region was the same as many SCCmec of Staphylococcus aureus. WC28 SCCmec abutted an incomplete SCC element with a novel allotype of ccrC, which was closest (82% identity) to ccrC1 allele 9 in Staphylococcus saprophyticus strain ATCC 15305. Only two direct target repeat sequences, one close to the 3'-end of orfX and the other abutting the left end of WC28 SCCmec, could be detected.
CONCLUSIONS/SIGNIFICANCE: A new 35-kb SCCmec was characterized in a S. cohnii isolate, carrying a class A mec gene complex, new variants of ccrA5 and ccrB3 and two novel genes in the J1 region. This element is flanked by 8-bp perfect inverted repeats and is similar to type III SCCmec in S. aureus and a SCCmec in S. pseudintermedius but with different J1 and J3 regions. WC28 SCCmec was arranged in tandem with an additional SCC element with ccrC, SCC(WC28), but the two elements might have integrated independently rather than constituted a composite. This study adds new evidence of the diversity of SCCmec in CoNS and highlights the need for characterizing the 'non-typable' SCCmec to reveal the gene pool associated with mecA.
背景
许多凝固酶阴性葡萄球菌（CoNS）的 SCCmec 元件无法通过多重 PCR 进行分型。在一株表皮葡萄球菌分离株中遇到了一种“不可分型”的 SCCmec。
方法/主要发现：耐甲氧西林表皮葡萄球菌临床分离株 WC28 的 SCCmec 类型无法通过多重 PCR 进行分配。使用新设计的引物扩增 ccrA 和 ccrB 基因。通过三个重叠的长距离 PCR 获得整个 SCCmec，针对区域从左反向重复（IRL）到 ccrA/B，从 ccrA/B 到 mecA，从 mecA 到 orfX。使用反向 PCR 以自连接酶限制的 WC28 片段作为模板来鉴定 IRL 相邻区域。WC28 SCCmec 具有 A 类 mec 基因复合物（mecI-mecR1-mecA）。ccrA 和 ccrB 基因与溶血葡萄球菌菌株 H9 的 ccrA（SHP）最接近（89.7%同一性），与中间葡萄球菌菌株 KM241 的 ccrB3 最接近（90%同一性）。在 J1 区域发现了两个可能编码 AAA 型 ATP 酶的新基因，在 J2 区域存在一个 ψTn554 转座子，而 J3 区域与许多金黄色葡萄球菌的 SCCmec 相同。WC28 SCCmec 与一个不完整的 SCC 元件相邻，该元件具有新型 ccrC 同种型，与腐生葡萄球菌菌株 ATCC 15305 的 ccrC1 等位基因 9 最接近（82%同一性）。只能检测到两个直接的靶重复序列，一个靠近 orfX 的 3'末端，另一个与 WC28 SCCmec 的左端相邻。
结论/意义：在表皮葡萄球菌分离株中鉴定出一种新型 35-kb SCCmec，携带 A 类 mec 基因复合物、ccrA5 和 ccrB3 的新变体以及 J1 区域的两个新基因。该元件两侧为 8 个碱基对的完美反向重复序列，与金黄色葡萄球菌的 III 型 SCCmec 和中间葡萄球菌的 SCCmec 相似，但 J1 和 J3 区域不同。WC28 SCCmec 与带有 ccrC 的附加 SCC 元件（SCC（WC28））串联排列，但这两个元件可能是独立整合的，而不是构成复合的。本研究为 CoNS 中 SCCmec 的多样性增加了新的证据，并强调需要对“不可分型”的 SCCmec 进行表征，以揭示与 mecA 相关的基因库。
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