Corynebacterium nigricans sp. nov.: proposed name for a black-pigmented Corynebacterium species recovered from the human female urogenital tract

Abstract

Six independent isolates of an unusual black-pigmented Corynebacterium species (strains CN-1, CN-2, CN-3415, W70124, 91-0032, and 92-0360) were recovered from the human female urogenital tract. Four of the six source patients had complications of pregnancy, including spontaneous abortion, preterm labor, and low amniotic fluid volume at the time of the pathogen isolation. One isolate was recovered from a vaginal ulcer. All six strains yielded black-pigmented colonies on sheep blood agar, chocolate agar, and colistin-nalidixic acid agar after 24 to 48 h of incubation at 35 degrees C. The dry, adherent colonies pitted the agar surface. The cells were coccobacillary to rod-shaped, catalase positive, nonmotile, and nonlipophilic. Only five of six isolates were available for characterization. Biochemical and chemotaxonomic studies revealed that the strains belong to the genus Corynebacterium but differ from known corynebacterial species. Comparative 16S rRNA gene sequence analysis showed that the strains are closely related and form a new subline within the genus Corynebacterium. We propose the name Corynebacterium nigricans sp. nov. for this group of coryneforms. The type strain of Corynebacterium nigricans is CN-1. It is deposited in the American Type Culture Collection (assigned strain number ATCC 700975) and in the Institute Pasteur collection (assigned strain number CIP 107346).

FIG. 1.

Black-pigmented colonies of C. nigricans CN-1 strain on a blood agar plate after 24 h. Reprinted with permission from reference .

FIG. 2.

Gram stain of C. nigricans strain CN-3415.

FIG. 3.

Maximum-likelihood cladogram of selected corynebacterial 16S rRNA sequences, including those of newly isolated C. nigricans strains. The 16S rRNA sequence of Mycobacterium tuberculosis (X55588) was chosen as an outgroup for this phylogenetic analysis. Sequences are identified by species name and GenBank accession number, if available. The presented tree is a consensus of 100 bootstrap replicates. Bootstrap values of maximum likelihood (ML) (100 replicates), minimum evolutionary distance (ME) (1,000 replicates), and parsimony analyses (PA) (1,000 replicates) are indicated for strongly supported branch points (i.e., bootstrap value of >75%). Taxa representative of the proposed C. nigricans species are labeled “C. nigricans group.” C. segmentosum and C. tuberculostearicum are not valid species names.