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Mode of origin of sulphonamide-resistant strains in B. dysenteriae Flexner
Published online by Cambridge University Press: 15 May 2009
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The change by which a strain of B. dysenteriae Flexner becomes resistant to sulphonamides is similar in character to the change in B. coli mutabile from 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 of B. typhosus on rhamnose and of certain coliform bacteria on arabinose may also be of the same nature.
Strains of B. dysenteriae Flexner 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.
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