Which penicillin variant targets both Gram-positive and some Gram-negative bacteria?

Piperacillin is a penicillin variant that is especially effective against a broad range of bacteria, including both Gram-positive and some Gram-negative organisms. It belongs to the extended-spectrum penicillin group, which makes it effective against certain Gram-negative bacteria, particularly Pseudomonas aeruginosa and other Enterobacteriaceae. This broad spectrum arises from its ability to resist degradation by some beta-lactamases that certain bacteria produce.

In contrast, the other options have more specialized uses. Cephalosporins are a different class of beta-lactam antibiotics that mainly target Gram-positive bacteria and have variable effectiveness against Gram-negative bacteria, depending on the generation. Nafcillin and Oxacillin are primarily used to treat infections caused by methicillin-sensitive Staphylococcus aureus (MSSA) and focus more on Gram-positive bacteria with limited activity against Gram-negative bacteria.

Thus, the ability of piperacillin to effectively target a wider range of bacteria, including specific Gram-negative species, is why it is the correct answer for this question.