A 75-year-old male develops a cough that produces blood-tinged sputum. He has a fever of 104degF. Gram-positive cocci in clusters are found in a sputum smear. A chest x-ray shows increased density in the right upper lobe. Of the following penicillins, which is most likely to be ineffective?

Ticarcillin resembles carbenicillin and has a high degree of potency against Pseudomonas and Proteusorganisms but is broken down by penicillinase produced by various bacteria, including most staphylococci. Oxacillin, cloxacillin, nafcillin, and dicloxacillin are all resistant to penicillinase and are effective against staphylococci.