efflux pump complex or subunit conferring antibiotic resistance metal transporters with antibiotic efflux ARO:3007657 antibiotic_resistance Efflux pumps also regulate the level of metal ions in the cytoplasm but are toxic when in excess. Metals often act as a facilitator in the proliferation and persistence of antibiotic resistance. Therefore, metal contamination in natural environments could have an important role in maintaining and promoting antibiotic resistance. The presence of metals co-selects for antibiotic resistance and leads to the development of cross-resistance. Micro-organisms adopt various mechanisms that may confer resistance against more than one antimicrobial, of which multidrug efflux systems are the most common.