Cephalosporins Are More Effective Than the Penicillins Against Gram-Negative Bacteria

Cephalosporins are more effective than the penicillins against Gram-negative bacteria because they

A) Are unable to penetrate the outer membrane through the porin molecules
B) Lack a beta-lactam ring
C) Have a longer half-life in vivo
D) Contain Cilastatin, which prevents destruction of the antibiotic by the kidneys
E) Are resistant to ?-lactamase enzyme activity