Which sulfonamide antibiotic was mentioned as effective against both gram-positive and gram-negative bacteria?

Sulfisoxazole is a sulfonamide antibiotic that has been noted for its effectiveness against a broad range of bacteria, including both gram-positive and gram-negative strains. As a member of the sulfonamide class, it works by inhibiting bacterial folic acid synthesis, which is necessary for nucleic acid production and ultimately bacterial growth. This mechanism of action allows sulfisoxazole to be effective in treating various bacterial infections caused by organisms such as Escherichia coli (a gram-negative bacterium) and Staphylococcus aureus (a gram-positive bacterium).

The other options do not represent sulfonamide antibiotics and have different mechanisms and spectra of activity. Penicillin primarily targets gram-positive bacteria and some gram-negative bacteria, while ciprofloxacin is a fluoroquinolone that also has broad-spectrum activity but is not a sulfonamide. Clindamycin is effective against many anaerobic bacteria and some gram-positive bacteria, primarily streptococci and staphylococci, but it does not have the same broad spectrum against gram-negative bacteria as sulfisoxazole does. Thus, sulfisoxazole stands out for its relevance to both types of bacteria in the context of sulfonamide antibiotics.