Colistin-induced surface changes in the cells of Proteus spp.

The effects of colistin on some strains of Proteus mirabilis, P. morganii and P. vulgaris are described. Two strains of P. mirabilis, NCTC 60 and NCTC 4199, took up greater amounts of colistin from solution than did the other strains. Pretreatment of strains 60 and 4199 resulted in osmotic instability and in increased susceptibility to Tris and deoxycholate. Colistin‐induced lysis in Tris could be overcome by means of 0–16 mol/l sodium chloride or 0–33 mol/l sucrose. Pre‐treated, but not control, cells of these two strains exposed to Tris (0–05 mol/l, pH 9) developed surface protuberances (blebs).