1. Target modification (PBPs)- mutational target modification (Neisseria gonorrhoeae, Streptococcus pneumoniae); chromosomal- acquisition of a new target, PBP2 (Methicillin resistant Staphylococcus aureus); transposon

2. Drug inactivation (lactamases)- plasmid and chromosomal (Enterobacteriacae)

3. Drug uptake/efflux- modification of cell wall/carrier proteins; chromosomal (Pseudomonas aeruginosa)