Self-resistance of Colistin-producing Bacillus colistinus. II. Effect of Colistin on Protoplasts and Liposomes Derived from Colistin-producing Bacillus colistinus

Abstract

Protoplasts of colistin-producing Bacillus colistinus 11-4 were more susceptible to the bactericidal action of colistin than the whole cells. However, protoplasts of strain 11-4 were still moreresistant to the colistin-induced lysis than spheroplasts of colistin-sensitive E. coli. The osmotic sensitivity ofprotoplasts of B. colistinus 11-4 was also resistant to treatment with 100 /zg/ml colistin. Liposomes of lipid extracted from B. colistinus 11-4 were resistant to colistin as compared with those from E. coll. The phospholipid content of the extracted lipid of strain 11-4 was one-half that of E. coli lipid, and the phospholipid content of colistin-sensitive mutants increased with increasing sensitivity. These results suggest that the cytoplasmic membraneof B. colistinus is inherently resistant to colistin and this resistance may be associated with phospholipid.