We tested the ability of 62 growing strains belonging to the class to reduce the redox indicator and free-radical generator 1,1'-dibenzyl-4,4'-bipyridinium dichloride (benzyl viologen [BV]) to a blue-violet-purple color. BV was reduced by 12 but not by PN525 (T = type strain). BV was also reduced by five of nine and by four of six species. BV was not reduced by 19 species, six species, five unnamed strains belonging to different serogroups, three species, and one unnamed strain. The BV-reducing ability was localized in the membrane of B-PG9 and was dependent on NADH. Reduction of BV could be expressed in mixed cultures, and this activity may be useful for recognizing the contaminating presence of an species. The reductive BV response may have phylogenetic value. We believe that the test described in this paper readily distinguishes all species and some and species from all , and species tested.


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