MSSA

Q. Which of the listed antibiotics is the drug of choice for methicillin-sensitive staphylococci?
A. Vancomycin
B. Cefazolin
C. Linezolid
D. Ampicillin
E. Penicillin

Ans:  B.

Vancomycin and linezolid will cover methicillin-sensitive staphylococci, but should be reserved for methicillin-resistant organisms. Penicillin and ampicillin are increasingly ineffective against S. aureus, as the introduction of penicillin in the early 1940s selected for penicillinase-producing strains. Approximately 85 to 90% of S. aureus strains in both the hospital and the community are now resistant to penicillin/ampicillin. The firstgeneration cephalosporins (e.g., cefazolin) will cover methicillin sensitive strains of S. aureus. Of note, cefazolin has poor penetration into the CNS, and nafcillin should be used instead of the former in the case of staphylococcal meningitis.

EXTA EDGE:

·         MRSA has carriage rates as high as 25 to 50%.

·         Groups at higher risk for MRSA include injection drug users, persons with insulin-dependent diabetes, patients with dermatologicconditions, patients with long-term in-dwelling intravascular catheters, and healthcare workers.

·          S. epidermidis species tend to be much more antibiotic resistant than S. aureus species, with a methicillin resistance rate of approximately 80%