The somatic antigens of theCl. welchiigroup of organisms

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Abstract
The complex group of organisms with cultural and biochemical properties closely similar to the classical Cl. welchii are at present differentiated into four types according to the quality and number of the toxins they elaborate in vitro.The present study is concerned with the specific affinities of the bacterial antigens of representative strains from these four types. The experiments confirm earlier reports concerning a wide diversity in the specificity of the somatic antigens of the classical type A strains. The bacterial antigens of the types B, C and D, however, have been shown to possess interesting similarities and affinities:(1) The O antigen of type A (classical Cl. welchii) strains is strictly strain specific.(2) The type B (L.D. bacillus) strains isolated in Great Britain share an identical O antigen but a strain from South Africa had a strictly specific O component.(3) The O antigen of the type C (B. paludis) strains isolated in Great Britain is identical.(4) The type D (B. ovitoxicus) strains exhibit wide diversity in the specificity of their O component. Thirteen strains were placed in not less than seven groups.(5) Cross O reactions between various types is negligible or entirely absent.(6) In addition to the heat-stable O antigen certain strains possess a heat-labile somatic component. This antigen occurs only among those types (B and D) that produce ɛ toxin but it is probably not present in all strains.(7) Colony variants reminiscent of the typical rough forms of Gram-negative organisms are frequently encountered among strains of each type. Certain of these forms appear as stable variants and they are characterized serologically by the loss of O antigen specific for the strain.(8) The rough forms still produce toxins characteristic of the type to which the parent culture belongs.

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