Methicillin-resistant Staphylococcus aureus (MRSA), a gram-positive bacteria, is an important pathogen, posing a global health threat. Resistance to the antibiotic methicillin develops when a susceptible bacterial strain of S. aureus (MSSA) acquires a resistance gene, mecA, which is carried on a mobile genetic element, referred to as Staphylococcal Cassette Chromosome mec (SCCmec). It has been hypothesized that MRSA originated through the horizontal gene transfer of SCCmec from another species, S. epidermidis O7.1, to MSSA. However, it remains unclear whether it was a single transfer event, or whether such transfer can occur repeatedly. Understanding this would be important for MRSA control. In this project we examine publicly available genomes of S. aureus and related species to determine presence of mecA genes and to visualize the distribution of this gene among strains using the phylogenetic tree approach.