Antifungal Properties of the Polymyxins

Abstract

Previous investigations with the various polymyxins have established the marked effectiveness of these antibiotics against Gramnegative bacteria( 1-3). In view of the antifungal properties possessed by certain aliphatic fatty acids, the isolation of a fatty acid component from the polymyxins (4) suggested a study of these antibiotics for similar properties. Identification of the acid as an isomer (6-methyl-octan-l-oic acid) of pelargonic acid (5) added further interest in light of the work reported by Rothman and co-workers(6,7), who found pelargonic acid to be quite prominent in a group of highly active normal aliphatic monobasic acids isolated from hair fat of adults.I n the present study, the relative antifungal activities have been determined for polymyxins A, B, D and E. Several known antifungal agents were included for purpose of comparison. While the investigation was in progress, Serri (8) reported on the activity of areosporin (polymyxin B) against a number of dermatomycetes. The antibiotic showed greatest activity against Achorion schoenleini, was less active but equally so against Trichophyton gypseum asteroides, Microsporum audouini, Microsporum felineurn and Sporotrichum gougeroti, and least active against Trichophyton rubrum, Trichophyton craterif orme and A chorion quinqueanurn.Experimental. Preliminary determinations of the antifungal properties of the polymyxins* were carried out by means of 'the agar cup-plate method of Burlingame and Reddish (9). A serial dilution technic was used to ascertain fungicidal activity. Known antifungal agents included in the study were: benzoic acid, salicylic acid, undecylenic acid, * Polymyxin B as bhe sulfate was kindly supplied by Chas. Pfizer and Co. and assayed a t 7625 U/mg. The remaining polymyxins were prepared in our laboratories as the hydrochlorides, by Dr. H. A. Nash wit,h the following potencies: polymyxin A, 9425 U/mg; polymyxin D, 1526 U/mg; polymyxin E, 9500 U/mg. G-4t and A4sterol.: Fungistatic procedure. Sabouraud's maltose agar was used in the agar cup-plaste method, each agent being tested in plain medium and in the medium containing 10% normal horse serum. The diameter of the cup was 1.5 cm. Inocula consisted of 5day-old cultures of the respective test organisms, i.e., Candida albicans, Trichophyton mentagrophytes and Debaryomyces neoformans. Solutions of each agent were made up at a concentration of 0.1% in 95% ethyl alcohol, from which 0.1 cc was pipetted into the cup. Control tests on the alcohol solvent were included in each run. Plates were covered with unglazed clay tops and incubated for 5 days at 28°C. The extent of growth inhibition was measured in millimeters from the edge of the cup to the periphery of the cleared zone. Fungicidal Focedure. The medium consisted of 1% neopeptone and 4% maltose, adjusted to pH 5.6. As in the fungistatic procedure, determinations were made in both plain medium and in broth containing 10% normal horse serum. Stock solutions of the respective test materials were prepared in 95% ethyl alcohol at a concentr...