Asked by: Katrine Mellersh, Durham
Lots of chemicals kill bacteria (bacteriocidal compounds), or slow down their replication (bacteriostatic compounds), for example bleach or cyanide. The trick is finding those that don’t do the same to humans. These ‘antibiotics’ can work in many ways: they simply need to disrupt something specific to bacterial biochemistry.
One easily reached feature is the mesh surrounding the bacterium: the cell wall. It’s made by linking together simple sugars and short amino acid chains. Many classes of antibiotics (including cephalosporins and penicillins) work because they strongly bind onto (so clog up) the bacterial machinery that links the chain-ends together. Alternatively, vancomycin binds to the amino acid chain-ends themselves, while bacitracin prevents the bacteria from moving its cell wall chemicals to the outside.
Another major target is the ribosome, that intricate combination of molecules that assembles proteins (the cell’s working machines) from DNA. Bacterial and non-bacterial ribosomes differ quite a lot in molecular structure. Antibiotic drugs like tetracycline, erythromycin, streptomycin and neomycin bind to bacterial ribosomes, clogging them up so that proteins can’t be made. The bacterium eventually stops functioning. Many other antibiotic mechanisms exist. For example, quinolones block the bacterial DNA untangling machinery, while sulfonamides block folate production (needed for making DNA).