A 44-year-old man develops intra-abdominal sepsis after undergoing difficult bowel resection and anastomosis. He is initially given ceftizoxime sodium (Cefizox), which is in effective because of overgrowth of which of the following?

Ceftizoxime (Cefizox) is not effective against many strains of Pseudomonas. If the drug is used, a higher dosage may be indicated, and the antibiotic should be changed if a quick response does not occur. Complications may occur in patients who are allergic to penicillin.