In vitro antibiotic activity of 11 beta-lactam antibiotics in a cancer center.

Two-thousand, five-hundred and twenty-four bacterial isolates were tested against 11 new beta-lactam antibiotics in a prospective study conducted in a cancer center. E. coli, P. aeruginosa, and K. pneumoniae were the most common gram-negative organisms isolated, while S. aureus and Enterococcus were the most common organisms among the gram-positive. The new cephalosporins were more active than the semisynthetic penicillins against E. coli, P. aeruginosa, and K. pneumoniae (p less than 0.001). Mezlocillin had better activity than the other semisynthetic penicillins against most of the gram-negative organisms as well as the enterococci. As a result, mezlocillin was preferred as a beta-lactam agent to be employed with an aminoglycoside as empiric antibiotics for febrile patients with neoplasia.