Which ointment is a cationic polypeptide used for MRSA?

Which ointment is a cationic polypeptide used for MRSA?

• A. Bacitracin ointment
• B. Erythromycin ointment
• C. Neomycin/Polymyxin/Dexamethasone
• D. Tobramycin/Dexamethasone

Answer: (A)

Cationic polypeptide antibiotics used topically target Gram-positive bacteria, including many Staphylococcus species responsible for skin infections. Bacitracin fits this description: it is a cationic polypeptide antibiotic that disrupts cell wall synthesis by inhibiting dephosphorylation of bactoprenol, making it effective against Staph species when applied as an ointment for superficial skin or ocular infections. This topical use is why it’s the best choice for addressing MRSA in a surface infection setting. Erythromycin ointment is a macrolide that inhibits protein synthesis, not a cationic peptide, and MRSA resistance reduces its utility. The Neomycin/Polymyxin/Dexamethasone combination includes polymyxin B, a cationic peptide, but its primary role is broad coverage including Gram-negatives and it isn’t the classic agent singled out for MRSA among these options. Tobramycin/Dexamethasone contains an aminoglycoside, not a cationic polypeptide.

Cationic polypeptide antibiotics used topically target Gram-positive bacteria, including many Staphylococcus species responsible for skin infections. Bacitracin fits this description: it is a cationic polypeptide antibiotic that disrupts cell wall synthesis by inhibiting dephosphorylation of bactoprenol, making it effective against Staph species when applied as an ointment for superficial skin or ocular infections. This topical use is why it’s the best choice for addressing MRSA in a surface infection setting.

Erythromycin ointment is a macrolide that inhibits protein synthesis, not a cationic peptide, and MRSA resistance reduces its utility. The Neomycin/Polymyxin/Dexamethasone combination includes polymyxin B, a cationic peptide, but its primary role is broad coverage including Gram-negatives and it isn’t the classic agent singled out for MRSA among these options. Tobramycin/Dexamethasone contains an aminoglycoside, not a cationic polypeptide.