Our paper is about the world's most notorious hospital pathogen, methicillin-resistant Staphylococcus aureus (MRSA) to which even our best antibiotics, penicillins and cephalosporins, are ineffective.  S. aureus is usually a benign member of our normal flora, but it is transformed into MRSA when a unique mobile genetic element called staphylococcus cassette chromosome mec (SCCmec) is integrated into the chromosome. We named it as such because it is a considerably big element of 20~60 kilobases and precisely integrated to and excised from the fixed site of S. aureus chromosome. The paper demonstrated that there are at least three molecular types in SCCmec, and thus there are at least three distinct MRSA clones in the world. Now the SCCmec typing has become an important tool in the field of world-wide molecular epidemiology of MRSA strains. I think this is the reason why the paper is highly cited recently.

The paper showed unequivocally that there are multiple clones of MRSA in the world by describing that either one of the three distinct SCCmec elements is integrated in each MRSA strain. This also opened up a new methodology for molecular typing of MRSA in the world.

I started my study on MRSA in 1989. At that time the methicillin-resistance gene, mecA, had been cloned by Matsuhashi's group in Tokyo University. The gene mecA was not found in methicillin-susceptible S. aureus. Therefore, it was suspected that mecA was acquired from other bacterial species by lateral gene transfer. I wanted to know how the mecA gene came into S. aureus chromosome. So I and my colleague Teruyo Ito started cloning and sequencing of the chromosome regions around mecA gene using a Japanese MRSA strain. We completed sequencing and realized that the mecA gene was carried by a novel genetic element distinct from any of the previous families of mobile genetic elements such as transposons, bacteriophages, conjugative plasmids, etc. Subsequent genetic experiments demonstrated the movement of the element, and we designated it SCCmec. Then, by analyzing the MRSA strains of 20 countries, we realized that the type of SCCmec (now type-II is assigned for this type) was detectable only in Japanese and certain American MRSA strains. We therefore started to clone and sequence all of these non-type-II SCCmec. Old British MRSA strains had a distinct type of SCCmec (type-I), and another group of strains distributed widely in England, Europe, and South East Asian countries (we call it "British Empire Strain" ) had another type of SCCmec (type-III). The three types covered more than 90% of the MRSA strains from 20 countries. We submitted the results to AAC which is the one discussed here.