Antibiotic resistance. Illustration of the molecular mechanism of antibiotic resistance. At left, an antibiotic (streptomycin, green) passes through the bacterial wall (white arrow) through the channel protein porin, leading to the death of the bacteria (lower left). At right, the gram-negative bacteria have developed resistance and expel the streptomycin molecules through a membrane protein pump (white arrow), in this case 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.