This is an increasingly common question, as methicillin-resistant Staphylococcus pseudintermedius (MRSP - essentially the canine version of the high-profile human "superbug" MRSA) has expanded greatly in the canine population. As more dogs get MRSP infections and even more become inapparent carriers of this bug, more dogs that are carriers will need surgery (both elective and non-elective). Since MRSP is now a leading cause of surgical site infections in dogs, there's concern about what to do with these carriers, particularly when it comes to elective surgeries like spays and neuters.
My answer to the question is... maybe.
If the dog has an active MRSP infection (e.g. skin infection), I'd say "hold off for a while" if possible. I don't like elective surgeries being done on animals with active infections (this applies to almost any kind of infection, not just MRSP). If an animal has an active MRSP infection, it might increase the risk of the surgical site becoming infected because of the greater overall burden of MRSP on the skin and elsewhere.
If the dog doesn't have an active infection (e.g. is a healthy carrier after having gotten over a previous MRSP infection), I'd say "go ahead."
- Spay-associated infections are quite rare.
- We don't use antibiotics prophylactically (i.e preventatively) for spays (or at least, they shouldn't be used for this kind of low-risk procedure - unfortunately some people still use them inappropriately).
- MRSP is no more likely to cause a spay infection than methicillin-susceptible S. pseudintermedius. It's just harder to kill when an infection occurs.
- Methicillin-susceptible S. pseudintermedius can be found on almost all dogs.
So, if infections are rare, despite the fact that S. pseudintermedius is present on pretty much all dogs and that we don't use drugs to kill S. pseudintermedius during (or after) spays, there should be no added risk of infection by the antibiotic-resistant version of this bug.
Every dog is carrying lots of different bacteria that can cause an infection at any time. That's why we use a variety of surgical antisepsis practices (e.g. clipping, scrubbing, sterile instruments, proper operating room) to help prevent a critical number of bacteria from getting into the sterile surgical site where they can start to cause problems.
This strategy doesn't necessarily apply to surgeries where antibiotics are used prophylactically and where staph are the main causes of infection, especially in situations like orthopedic procedures where MRSP infections are common and can be very hard to treat. What to do in those cases with an MRSP-positive animal is a tougher question, and we're working on an answer to it at the moment.