Cephalosporins are LAME, because they don't cover these organisms:
L listeria monocytogenes
A atypicals (mycoplasma, chlamydia)
Listeria is not susceptible to cephalosporins of any generation.
Cephalosporins have no effect against Legionella, Mycoplasma, Chlamydia (atypicals)
The reason enterococci are resistant to cephalosporins is thought to be mainly due to alterations of penicillin-binding proteins and secondly production of a beta-lactamase.