Catabacter hongkongensis gen. nov., sp. nov., isolated from blood cultures of patients from Hong Kong and Canada

Abstract

Four bacterial isolates were recovered from the blood cultures of four patients, two of whom were from Hong Kong and two of whom were from Canada. The two Hong Kong strains were isolated from a 48-year-old man with intestinal obstruction and secondary sepsis (strain HKU16T) and from a 39-year-old man with acute appendicitis (strain HKU17), while the two Canadian strains were isolated from a 74-year-old man with biliary sepsis (strain CA1) and from a 66-year-old woman with metastatic carcinoma and sepsis (strain CA2). While the first three patients survived, the last patient died 2 weeks after the episode of bacteremia. All four isolates are strictly anaerobic, nonsporulating, gram-positive coccobacilli that were unidentified by conventional phenotypic tests and commercial identification systems. They grow on sheep blood agar as nonhemolytic pinpoint colonies after 48 h of incubation at 37 degrees C in an anaerobic environment. All are catalase positive and motile, with flagella. They produce acid from arabinose, glucose, mannose, and xylose. They do not produce indole or reduce nitrate. They are sensitive to penicillin, vancomycin, and metronidazole but resistant to cefotaxime. 16S rRNA gene sequence analysis showed 16.0%, 16.8%, and 21.0% base differences from Clostridium propionicum, Clostridium neopropionicum, and Atopobium minutum, respectively. The G+C content of strain HKU16T is 40.2% +/- 2.2%. Based on their phylogenetic affiliation, unique G+C content, and phenotypic characteristics, we propose a new genus and species, Catabacter hongkongensis gen. nov., sp. nov., to describe the bacterium, for which HKU16 is the type strain, and suggest that it be assigned to a new family, Catabacteriaceae. The gastrointestinal tract was probably the source of the bacterium for at least three of the four patients. The isolation of a catalase-positive, motile, nonsporulating, anaerobic gram-positive bacillus in clinical laboratories should raise the possibility of C. hongkongensis. Further studies should be performed to ascertain the epidemiology and other disease associations of this bacterium.

FIG. 1.

Flagellum stain (a) of Catabacter hongkongensis. The bacterium is a gram-positive coccobacillus with a tuft of flagella inserted on one side (arrows). (b) Scanning electron micrograph of Catabacter hongkongensis. The bacterium is short and straight and tapered at both ends. Cells vary in length from 0.71 to 1.12 μm and in diameter from 0.36 to 0.48 μm (mean, 0.96 μm by 0.42 μm; n = 20). Bar, 0.5 μm.

FIG. 2.

Phylogenetic tree showing the relationships of Catabacter hongkongensis gen. nov., sp. nov., to related anaerobic gram-positive bacteria. The tree was constructed by using the neighbor-joining method, with Bacteroides fragilis as the root. Bootstrap values were calculated from 1,000 trees. Bar, estimated number of substitutions per 100 bases, using the Jukes-Cantor correction. Names and accession numbers are given as cited in the GenBank database.