Antimicrobial Actions ofHexachlorophene: Inhibition of Respiration inBacillus megaterium1

Hexachlorophene (HCP)inhibits bothendogenous andexogenousrespiration (oxygen uptake) inBacillus megaterium, without sparing byany ofseveral substrates. Theinhibition ismaximal whenthecells aretreated with8ggofHCP permg ofcells (dry weight), whichcorresponds totheminimal lethal dose. Levels aslowas2Ag/mg areinhibitory butnotlethal. HCPalso inhibits therespiration ofisolated B.megaterium membranes andcan acton several components ofthe electron transport chaininthemembranes andon soluble enzymes.-Although bothformsofnicotinamide adenine dinucleotide, reduced formdehydrogenase andmalic dehydrogenase areinhibited byHCP,they areless susceptible thanis oxygen uptake. Thesite ofmaximalsensitivity isnearertheterminal electron acceptor, buttheexactlocation depends on thecytochrome composition ofthe membranes. Ifcytochromes b,, a,anda, arepresent, butnoto,HCP inhibits electron transport on thesubstrate sideofcytochrome b,; ifcytochromes bl, a,, ando are present, butnota, theinhibition occurs on theoxygen sideof cytochrome b . Exogenous menadione, an analogue ofmenaquinone, reversesthe inhibition inbothcircumstances. Theprimary lethal action ofHCPthus appears toberespiratory i,nhibition ata site within themembrane-bound partofthe electron transport chain.