regulates porin OmpF AcrAB-TolC protein(s) and two-component regulatory system modulating antibiotic efflux ramA antibiotic_resistance ARO:3000823 ramA RamA (resistance antibiotic multiple) is a positive regulator of AcrAB-TolC and leads to high level multidrug resistance in Klebsiella pneumoniae, Salmonella enterica, and Enterobacter aerugenes, increasing the expression of both the mar operon as well as AcrAB. RamA also decreases OmpF expression.