Which antibiotic is active against Pseudomonas species as well as indole-positive Proteus bacteria?

Explanation

Carbenicillin is a broad-spectrum penicillin effective against Pseudomonas and indole-positive Proteus species, while methicillin and oxacillin target primarily Gram-positive bacteria. Lincomycin and erythromycin are less effective against these Gram-negative organisms.