Methicillin resistance in S. aureus is defined as an Oxacillin (MIC) > 4
microgram/mL. Isolates resistant to oxacillin or methicillin are also
resistant to all beta - lactam agents including cephalosporins.
The mecA gene responsible for methicillin resistance
Staphylococcal cassette chromosome (SCCmec).
There are five SCCmec types (I-V) that vary in genetic
makeup and size.
Hospital Associated Community Associated
HA - MRSA CA - MRSA
type I, II, or III SCCmec type IV SCCmec
does not carry the multiple antibiotic
Sensitive to Bactrim, Clindamycin &
Multiple antibiotic resistance 50% fluoroquinolones.
•SCCmec type IV CA-MRSA
Prolonged hospitalization •MRSA USA300
Prior skin infection
Previous antibiotic use
Illicit drug use
A higher body mass index
Cosmetic body shaving
Physical contact with a person who has
a draining lesion or is a carrier of MRSA
Sharing equipment that is not cleaned
or laundered between users
Antibiotic use within three months before admission.
Hospitalization during the past 12 months.
Diagnosis of skin or soft-tissue infection at admission