Southern hybridization analysis of the mecA deletion from methicillin-resistant Staphylococcus aureus.

Genomic organization of methicillin-resistant Staphylococcus aureus strains and their methicillin-susceptible subclones were analyzed by pulsed-field gel electrophoresis and Southern hybridization with DNA fragments of methicillin-resistance gene mecA and an insertion element IS431 as probes. The entire mecA gene was deleted in all the seven methicillin-susceptible subclones studied, and the size of the deletion varied from 20 to 100 kilobases depending on each subclone. In six of the seven subclones, however, the downstream deletion end points were confined within a 2.0 kilobase HindIII-HindIII fragment containing a part of IS431 which was located 2.6 kilobase downstream of mecA gene. The results indicated that the intramolecular transposition of IS431 is responsible for the mecA deletion in methicillin-resistant Staphylococcus aureus.