For MSSA infections, what is the preferred class of antibiotics?

For MSSA infections, what is the preferred class of antibiotics?

• A. Tetracyclines
• B. Macrolides
• C. Cephalosporins
• D. Antistaphylococcal penicillins

Answer: (D)

This question tests selecting an antibiotic class that is most reliable against methicillin-susceptible Staphylococcus aureus by using agents built to withstand the bacteria’s penicillinase. Antistaphylococcal penicillins (such as nafcillin, oxacillin, and dicloxacillin) are specifically designed to resist staphylococcal beta-lactamase and to have strong activity against MSSA. They effectively inhibit cell-wall synthesis and are typically bactericidal against MSSA, which is why they’re the preferred choice for these infections. Tetracyclines and macrolides, while active against some S. aureus strains, are less reliable due to higher rates of resistance and often slower bactericidal activity. Cephalosporins can cover MSSA but aren’t as consistently dependable as the penicillinase-stable penicillins for serious MSSA infections. Therefore, the antistaphylococcal penicillins provide the best balance of stability to the bacteria’s resistance mechanism and potent activity against MSSA. If MRSA were a concern, different agents would be needed.

This question tests selecting an antibiotic class that is most reliable against methicillin-susceptible Staphylococcus aureus by using agents built to withstand the bacteria’s penicillinase. Antistaphylococcal penicillins (such as nafcillin, oxacillin, and dicloxacillin) are specifically designed to resist staphylococcal beta-lactamase and to have strong activity against MSSA. They effectively inhibit cell-wall synthesis and are typically bactericidal against MSSA, which is why they’re the preferred choice for these infections.

Tetracyclines and macrolides, while active against some S. aureus strains, are less reliable due to higher rates of resistance and often slower bactericidal activity. Cephalosporins can cover MSSA but aren’t as consistently dependable as the penicillinase-stable penicillins for serious MSSA infections. Therefore, the antistaphylococcal penicillins provide the best balance of stability to the bacteria’s resistance mechanism and potent activity against MSSA. If MRSA were a concern, different agents would be needed.