Bacterial wall and antibiotic resistance. Illustration of the molecular mechanism of antibiotic resistance. Here, the gram-negative bacterium has developed resistance and is expelling the antibiotic molecules (streptomycin, green) through a membrane protein pump. In this case the protein channel is the TolC efflux pump (purple-blue structure). Antibiotic resistance can occur over time through the overuse of antibiotic drugs. Resistant microbes require alternative drugs or higher doses of antibiotics. For an image showing the molecular mechanism of antibiotic resistance, see F013/1538.