A Fluorescent Derivative of Polymyxin: its Preparation and Use in Studying the Site of Action of the Antibiotic

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Abstract
A fluorescent derivative of polymyxin (DANSP) was prepared by coupling 1-dimethylaminonaphthalene-5-sulphonyl chloride with the γ amino group of αγ diaminobutyric acid radicals in the polymyxin molecule. As in the case of polymyxin, DANSP is readily absorbed by polymyxin-sensitive organisms and is rapidly bactericidal; cells can be protected against this bactericidal activity by pretreatment with certain cations. Mechanical disintegration of DANSP-treated cells showed that the fluorescent compound was associated with two fractions: (a) cell walls and (b) small particles. Fractionation of three strains of Pseudomonas aeruginosa showed that the fluorescent conjugate was equally distributed between the two fractions, but in the case of three Gram-positive, lysozyme-sensitive, organisms 90 % of the fluorescent conjugate was found in the small particle fraction; controlled lysozyme treatment of these cells showed that the DANSP was associated with a membrane underlying the cell wall from which the small particle fraction is formed on mechanical disintegration.

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