The emergence and prevalence of MRSA, MRSP, and MRSS in pets and people
Part 1 of this two-part article will give you the information you need to understand methicillin resistance in veterinary practice. Next month in part 2, you'll learn how to diagnose and treat methicillin-resistant skin infections as well as implement measures to reduce the spread of infection.
WHAT IS METHICILLIN RESISTANCE?Methicillin is a beta-lactam antimicrobial introduced in the 1950s. It is relatively resistant to beta-lactamase, so it was used to treat penicillin-resistant staphylococci. However, bacterial resistance to methicillin emerged soon after its introduction.
Methicillin resistance is mediated by bacterial production of an altered penicillin-binding protein (PBP2a), which does not allow microbial binding of beta-lactam antibiotics. Therefore, methicillin-resistant isolates are resistant to all beta-lactam antibiotics (penicillins, cephalosporins, and carbapenems) and are also frequently resistant to other classes of antibiotics.1,2 The protein PBP2a is encoded by the mecA gene that resides on a mobile genetic element called the staphylococcal cassette chromosome mec (SCCmec).
A laboratory diagnosis of MRSP is actually done by testing for bacterial resistance against oxacillin, a similar antibiotic that is more stable for testing purposes.1,2 For S. aureus, cefoxitin has supplanted oxacillin as the marker for methicillin resistance.