Mici 4218 lecture 3 january 11, 2021 antimicrobial classes mechanisms of action & resistance. General mechanisms of resistance: altered permeability stop the drug from getting in. Inactivation / destruction of antibiotic: altered binding site, novel (new) binding sites, efflux (pumps) mechanisms, bypass of metabolic pathways. Cell wall synthesis inhibitors: beta lactams, penicillins, glycopeptides, vancomycin (clinical use, fosfomycin, cephalosporins, carbapenems. These are the 3 classes of cell wall synthesis inhibitors: beta lactam, glycopeptides, fosfomycin. The cephalosporin generation are decided based on their spectrum of activity, not that they are newer or older. The general rule of thumb is that as you move up the generations, you gain gram- negative activity, and you lose gram-positive activity. The 1st generation drugs have better gram- positive activity and less gram-negative activity. Lactam is their common structure within the three classes of drug. The image on the right shows the building block of peptidoglycan (a disaccharide - nam and nag - attached to a pentapeptide).