reduction in the expression/loss of porins. These mutations can result in reduced permeability/ complete exclusion of drugs from porins. Efflux pumps: The permeability of antibiotics is affected by the type and number of efflux pumps present. Some bacteria have MDR efflux pumps which allow bacteria to reject and export toxic compounds and thus can also allow them to resist antibiotics. MDR pumps can be specific to one antibiotic or may target a broad spectrum of antibiotics. A variety of families of efflux pumps are present in bacteria, such as the ATP-binding cassette (ABC) family, the multidrug and toxin extrusion (MATE) family, the major facilitator superfamily (MFS), the small multidrug resistance (SMR) family, the resistance-nodulation-cell division (RND) superfamily and the proteobacterial antimicrobial compound efflux (PACE) family. These pumps are responsible for the majority of induced resistance in bacteria.