Establishment and evaluation of the new typing systems for the epidemiological investigation in MRSA (Methicillin Resistant Staphylococcus Aureus) infections

本研究的目的是了解对MRSA菌株进行分型的最有用的方法，以便在由细菌引起的感染中进行流行病学研究。对96株MRSA和12株已知来源的甲氧西林金黄色葡萄球菌(MSSA)的6种分型系统进行了评价。对用限制性内切酶SMAI切割的基因组DNA进行脉冲场凝胶电泳法(PFGE)分析，根据电泳分离的DNA条带将菌株分为14个类型。98%的菌株有一个或多个质粒，DNA分子大小在1kb到40kb之间。一个非常有趣的发现是，87%的耐甲氧西林金黄色葡萄球菌都有24.3kb的plsmid。该质粒在MSSA中很少检测到。生化试验结果，即乳糖和蔗糖发酵，可将菌株划分为四个生物型，似乎具有有限的流行病学价值。在噬菌体分型中，只有10%的MRSA菌株对稀释到IRTD的一种或多种分型噬菌体(S)敏感。相比之下，73%的MSSA菌株是可分型的。用凝固酶(无细胞)中和试验(包括从I型到VIII型的抗血清)进行分型，结果令人失望，因为98%的菌株属于同一类型，即II型。以上总结的所有结果使我们得出如下结论：在MRSA感染的流行病学调查中，至少当我们要弄清楚污染的传播时，最有用的方法是结合PFGE对SMI消化的基因组DNA进行分析的结果，对血浆DNA进行分析，特别是那些大于20kb的DNA，并根据它们发酵乳糖和蔗糖的能力进行生物分型。

This study has been carried out to know the most useful way to " type " the MRSA strains for the epidemiological servey in the infections caused by the bacterium. Six typing systems of S. aureus have been evaluated for their utility for the each 96 MRSA and 12 MSSA (Methicillin Se-nstitive S. aureus) strains of known origins. Analysis by Pulsed Field Gel Electrophoresis (PFGE) for the genomic DNA cut with a restriction enzyme, SmaI, enabled us to classify the strains into 14 types based on the DNA bands separated by the electrophoresis. Ninty-eight per cent strains were revealed to have a plsmid or plasmids and molecular size of the DNA ranged from about lkb to 40kb. A very interesting finding was that 87% of the MRSA have, in common, a plsmid of 24, 3 kb. This plasmid was rarely detected in MSSA. Results of the biochemical tests, i. e., fermentation of lactose and sucrose, could classify the strains into the four biotypes which seemed to be of limited epidemiological value. In the phage typing, only 10% strains of MRSA were sensitive to one or more typing phage (s) diluted to IRTD. By contrast, 73% strains of MSSA were typable. Typing by coagulase (cell free) neutralization test (antisera from type I to type VIII inclusive were employed) gave a disappointing results for the purpose of epidemiological investigation, as the 98% strains belonged to a same type, type ii. All of the results summarized above led us to conclude as follows ; In the epidemiological investigation of the infections due to MRSA, at least when we are going to clarify the spread of contamination, the most useful way to " type " an isolate is combination of the results presented by analysis, by PFGE, for genomic DNA digested with SmaI, analysis of plasmic DNA, especially those which is larger than 20kb and biotyping based on their ability to ferment lactose and sucrose.