writersoul- MRSA can be classified a different species, but it is a bit tricky when dealing with bacteria because a single genetic mutation which can lead to a methicillin resistance can possibly be on a plasmid which would not necessarily be an entirely new species, but a “different type” of an existing organism. If however this mutation was introduces to the bacteria genome (ie, not a plasmid) it may be considered a new species.
A similar parallel can be draw from humans. Humans have restriction fragment length polymorphisms. All because you and I don’t have the exact same DNA sequence does not mean that we are different species.