Hanssen Anne-Merethe, Kjeldsen Gry, Sollid Johanna U Ericson
Department of Microbiology and Virology, Institute of Medical Biology, University of Tromsø, Tromsø, Norway.
Antimicrob Agents Chemother. 2004 Jan;48(1):285-96. doi: 10.1128/AAC.48.1.285-296.2004.
The mecA gene in Staphylococcus aureus is located on the genetic element staphylococcal cassette chromosome (SCC). Different SCCmecs have been classified according to their putative recombinase genes (ccrA and ccrB) and overall genetic composition. Clinical isolates of coagulase-negative staphylococci (CoNS; n = 39) and S. aureus (n = 20) from Norway, India, Italy, Finland, the United States, and the United Kingdom were analyzed by pulsed-field gel electrophoresis, which showed that most isolates were genetically unrelated. Cluster analyses of 16S rRNA gene and pta sequences confirmed the traditional biochemical species identification. The mecI, mecR1, mecA, and ccrAB genes were detected by PCRs, identifying 19 out of 20 S. aureus and 17 out of 39 CoNS isolates as carriers of one of the three published ccrAB pairs. New variants of SCCmec were identified, as well as CoNS isolates containing ccrAB genes without the mec locus. ccrAB and mec PCRs were verified by hybridization. Sequence alignments of ccrAB genes showed a high level of diversity between the ccrAB alleles from different isolates, i.e., 94 to 100% and 95 to 100% homology for ccrAB1 and ccrAB2, respectively. All of the ccrAB3 genes identified were identical. Genetically unique and sporadic methicillin-resistant S. aureus (MRSA) contained local variants of ccrAB gene pairs identical to those found in MR-CoNS but different from those in MRSA from other regions. Allelic variants of ccrAB in isolates from the same geographic region showed sequence conservation independent of species. The species-independent sequence conservation found suggests that there is a closer genetic relationship between ccrAB2 in Norwegian staphylococci than between ccrAB2 sequences in international MRSA and Norwegian MRSA. This might indicate that different staphylococcal species acquire these genes locally by horizontal gene transfer.
金黄色葡萄球菌中的mecA基因位于葡萄球菌盒式染色体（SCC）这一遗传元件上。不同的SCCmecs已根据其假定的重组酶基因（ccrA和ccrB）以及整体遗传组成进行了分类。对来自挪威、印度、意大利、芬兰、美国和英国的凝固酶阴性葡萄球菌（CoNS；n = 39）和金黄色葡萄球菌（n = 20）的临床分离株进行了脉冲场凝胶电泳分析，结果表明大多数分离株在基因上不相关。16S rRNA基因和pta序列的聚类分析证实了传统的生化菌种鉴定。通过聚合酶链反应（PCR）检测了mecI、mecR1、mecA和ccrAB基因，结果鉴定出20株金黄色葡萄球菌中有19株以及39株CoNS分离株中有17株是已公布的三种ccrAB对之一的携带者。鉴定出了SCCmec的新变体，以及含有ccrAB基因但无mec位点的CoNS分离株。通过杂交验证了ccrAB和mec PCR。ccrAB基因的序列比对显示，不同分离株的ccrAB等位基因之间存在高度多样性，即ccrAB1和ccrAB2的同源性分别为94%至100%和95%至100%。鉴定出的所有ccrAB3基因均相同。基因独特且散发的耐甲氧西林金黄色葡萄球菌（MRSA）含有与耐甲氧西林CoNS（MR-CoNS）中发现的相同但与其他地区MRSA中不同的ccrAB基因对的局部变体。来自同一地理区域的分离株中ccrAB的等位基因变体显示出与菌种无关的序列保守性。所发现的与菌种无关的序列保守性表明，挪威葡萄球菌中的ccrAB2之间的遗传关系比国际MRSA和挪威MRSA中的ccrAB2序列之间的遗传关系更密切。这可能表明不同的葡萄球菌菌种通过水平基因转移在当地获得了这些基因。
