Bordetella trematum

Characteristics

Bordetella trematum is a Gram-negative, capsulated, non-spore-forming, rod about 0.5 μm wide and 1.0-1.8 μm long, but rods as long as 2.4 μm have been observed. It grows aerobically at temperatures ranging from 25-42 °C, with optimal temperature for growth ranging from 35-37 °C. Microaerobic growth may be observed at optimal temperatures. It is motile via peritrichous flagella. B. trematum is catalase positive. It is unique in being oxidase negative, since all other species of Bordetella are oxidase positive.

Bordetella trematum may be cultured on horse blood agar, MacConkey agar, and Bordet–Gengou agar. When grown on Bordet–Gengou agar, which is the standard agar for Bordetella isolation, colonies are convex, pearly, smooth, almost transparent, and glistening, and are surrounded by a zone of hemolysis. When grown on blood agar, colonies are grayish cream to white, circular, and convex.

Metabolism

Little is known about the metabolism of the species B. trematum since it is relatively newly discovered. Like all Bordetella species, B. trematum is a chemoorganotroph and requires nicotinamide, organic sulfur such as cysteine, and organic nitrogen such as amino acids for growth by respiratory metabolism. Its metabolism is not saccharolytic, meaning it does not use any form sugar for energy. Six of the ten known strains are able to reduce nitrate to nitrite. It is indole negative and urease negative.

Taxonomy

DNA-rRNA hybridization was used to place B. trematum LMG 13506^T in the family Alcaligenaceae. Amplified ribosomal DNA restriction analysis revealed a 94% similarity between the B. trematum reference strain and the Bordatella reference species, B. pertussis. Later, additional evidence to determine placement at the genus level came from DNA-DNA hybridization of B. trematum strains LMG 13506 and LMG 14446 against reference strains of other Bordetella and Alcaligenes species. Results showed the species B. trematum to be most like members of the genus Bordetella. SDS-PAGE analysis of whole-cell proteins allowed for development of a dendrogram displaying that Bordetella is not monophyletic. DNA-rRNA hybridization and 16S rRNA sequence analysis shows a close relationship between Bordetella and Alcaligenes. It is often difficult to differentiate between the two genera; in fact, some species across the genera are phenotypically identical.

Bordetella trematum and B. holmesii are the only species that do not colonize the respiratory tract. B. pertussis and B. parapertussis are respiratory pathogens that cause pertussis. B. bronchiseptica and B. avium are respiratory pathogens of other animals. B. hinzii is not pathogenic and colonizes the respiratory tract of birds. B. holmesii has been isolated from human blood. Members of the genus Alcaligenes colonize humans, but not the respiratory tract, and soil and water.

Genomics

The B. trematum genome was sequenced in 2013, and is currently undergoing annotation. The genome is estimated to possess 4,145 coding sequences with the majority of sequences coding for amino acids, amino acid derivatives, and carbohydrate pathways. About 184 genes are predicted to be involved in membrane transport. It has a 64-65% GC content. The total genome size is not currently known.

Pathogenicity

Bordetella trematum is a nonpathogenic, opportunistic organism whose sole source of isolation is open, human wounds. It can be ridded from the body without medical intervention.

Bordetella endotoxins are unique to the genus, species, and strain. B. trematum is the only Bordetella species with a semirough lipopolysaccharide which contains a single O-unit. The lipid A unit of B. trematum is identical to that of the opportunistic bacterium B. hinzii, but unlike any other Bordetella species.