Abstract
Serratia marcescens, normally suppressed by less than 100 ppm., was adapted to grow in 100,000 ppm. alkyl dimethyl benzyl ammonium chloride. Intense staining by Sudan Black B, increase in the ether-alcohol-soluble fraction, decreased electrophoretic mobility, and removal of resistance by lipase action, support the belief that the acquired resistance is dependent on increased lipid content of the resistant cell.