The organisms known as diphtheroid or pseudodiphtheritic bacilli form a loose ubiquitous group, and, owing to the inadequacy of present knowledge, one must still be conservative in regarding them as etiologic factors in the various diseases with which they are associated. Their relationship to the diphtheria bacillus is also unsettled. A number of observers1 have maintained that all the diphtheria-like bacilli, including the solidly staining types such as Bacillus hoffmanni, are variations of the same species, the differences in morphology, cultural characteristics and pathogenicity depending on environmental conditions. Others2 have included as diphtheroid bacilli those organisms that are identical with the Klebs-Loeffler bacillus in every respect except that they are nontoxic. This group has also been considered as an attenuated variety of the diphtheria bacillus which has lost its power of producing toxin.3
That B. diphtheriae is not always restricted to the mucous membranes was noted by
TOW A, WECHSLER HF. DIPHTHEROID BACILLUS AS THE CAUSE OF ACUTE ENDOCARDITIS. Am J Dis Child. 1932;44(1):156–161. doi:10.1001/archpedi.1932.01950080166016
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