Which antibiotic is commonly used to treat primarily Gram-positive infections with some Gram-negative coverage (e.g., E. coli)?

• A. Gentamicin
• B. Tetracycline
• C. Cefazolin
• D. Ciprofloxacin

Answer: (C)

Cefazolin is a first-generation cephalosporin, and its spectrum fits infections that are mainly due to Gram-positive organisms with some Gram-negative coverage. It has excellent activity against streptococci and methicillin-susceptible Staphylococcus aureus, which makes it a go-to for skin and soft tissue infections and for surgical prophylaxis. It also provides limited activity against Enterobacteriaceae, including E. coli, Klebsiella, and Proteus, but this coverage is modest compared with drugs that are stronger on Gram-negatives.

Choosing this drug is ideal when the infection is suspected to be driven by Gram-positive bacteria and you want some backup activity against a common Gram-negative organism like E. coli. In contrast, gentamicin targets Gram-negative bacteria predominantly and is not used as monotherapy for Gram-positive infections; tetracycline has broader activity but isn’t favored for typical E. coli coverage in acute infections due to resistance and other safety considerations; ciprofloxacin offers strong Gram-negative coverage but limited and less reliable Gram-positive activity for common skin/soft tissue infections.