Corynebacterium hindlerae sp. nov., derived from a human granuloma, which forms black colonies and black halos on modified Tinsdale medium but is not closely related to Corynebacterium diphtheriae and related taxa

Corynebacterium diphtheriae , Corynebacterium belfantii , Corynebacterium rouxii , Corynebacterium ulcerans , Corynebacterium pseudotuberculosis and Corynebacterium silvaticum are the only taxa from among ~121 Corynebacterium species deemed potentially able to harbour diphtheria tox genes. Subsequently tox-gene bearing species may potentially produce diphtheria toxin, which is linked to fatal respiratory distress if a pharyngeal pseudomembrane is formed or toxaemia develops in those unimmunized or under-immunized. Detection of diphtheria toxin-producing species may also invoke a public health response and contact tracing. Recovery of such species from the respiratory tract or other contaminated sources such as non-healing ulcerative wounds are expedited by use of differential and selective media such as modified Tinsdale medium (MTM). This medium is supplemented with potassium tellurite, which supresses most normal flora present in contaminated specimens, as well as l-cystine and thiosulphate. Most diphtheria-tox-gene bearing species grow well on MTM, producing black colonies with a black halo around each colony. This is due to an ability to produce cystinase in the presence of tellurite, cystine and thiosulphate, resulting in black tellurium deposits being observed in the agar. Other Corynebacterium species may/may not be able to grow at all in the presence of tellurite but if able to grow, will have small beige or brownish colonies which do not exhibit black halos. We describe here an unusual non-tox-gene-bearing isolate, NML 93-0612T, recovered from a human wrist granuloma, which produced black colonies with black halos on MTM agar but was otherwise distinguishable from Corynebacterium species which can bear tox genes. Distinctive features included its unusual colony morphology on MTM and sheep blood agar, by proteomic, biochemical and chemotaxonomic properties and by molecular methods. Its genome contained 2 680 694 bytes, a G+C content of 60.65 mol% with features consistent with the genus Corynebacterium and so represents a new species for which we propose the name Corynebacterium hindlerae sp. nov.