Mode of origin of sulphonamide-resistant strains inB. dysenteriaeFlexner

Abstract

The change by which a strain ofB. dysenteriaeFlexner becomes resistant to sulphonamides is similar in character to the change inB. coli mutabilefrom white (non-lactose-fermenting) to red (lactosefermenting).The highest proportion of variants are found in papillae, while no variants are found in the growing margin of colonies.Reversion does not take place during growth on sulphonamide-free media.The variation is a direct and heritable response to a chemical stimulus and in adaptation to this part of the environment.The variation described by Reiner Müller ofB. typhosuson rhamnose and of certain coliform bacteria on arabinose may also be of the same nature.Strains ofB. dysenteriaeFlexner resistant to sulphanilamide or sulphaguanidine 1/10,000 are only partially resistant to sulphathiazole 1/100,000 and to sodium sulphapyridine 1/10,000.Technique. The size of (uncrowded) colonies on a plate containing 1/10,000 sulphanilamide or sodium sulphacetamide is a useful criterion of resistance or non-resistance, but a resistant strain must be able to grow on 1/5000 Sa and will not grow on 1/5000 Ssac.The best culture medium for these tests is Lab. Lemco bouillon with agar, but without peptone.In concluding I wish to express my thanks for their help to Prof. H. R. Dean, Prof. C. H. Browning, Drs E. T. C. Spooner, A. MacDonald, J. E. McCartney and R. D. Stuart. The sulphonamides I received through the kindness of the British Pharmacopoeial Commission and of Messrs May and Baker.