Nature of the elimination of the penicillinase plasmid from Staphylococcus aureus by surface-active agents

Growth of Stapylococcus aureus in various ionic surface-active agents resulted in loss of the ability to produce penicillinase, whereas growth in nonionic surface-active agents had no effect on penicillinase production. The curing effect of various alkyl sulfates was found to be dependent upon the chain length. Curing by surface-active agents could be inhibited by magnesium. Reciprocal transduction experiments showed that curing by a surface-active agent was a property of the plasmid, not of the bacterial strain in which the plasmic resides.

Effect of polymyxin B on antibiotic-resistant Proteus mirabilis

The surface properties of polymyxin B-resistant Proteus mirabilis are markedly altered by the antibiotic. The effects include the development of susceptibility to surface-active agents such as deoxycholate or tris(hydroxymethyl)aminomethane and a marked increased osmotic fragility. However, cell wall impermeability to various agents such as erythromycin, actinomycin D, bacitracin, lysozyme, and triphenyltetrazolium chloride apparently remains intact. These results support the concept that the actions of the polymyxins on gram-negative bacteria are multiple; the action(s) of the antibiotic responsible for lethality in vitro, presumably at the level of the cytoplasmic membrane, may represent only a portion of the potential therapeutic effects of the antibiotic in vivo.