Listeria monocytogenes (and other Listeria species) is naturally resistant to most cephalosporins.

The mnemonic "LAME" is used to note organisms against which cephalosporins do not have activity: Listeria, Atypicals (including Mycoplasma and Chlamydia), MRSA, and enterococci. Fifth-generation cephalosporins are effective against MRSA, however.