Brucella canis are non-motile organisms and cannot move independently due to the absence of
flagella. Brucella are also non-
encapsulated, non-spore forming bacteria that replicate in the
ER of their host cells. The bacteria are Gram-negative coccobacilli or short rods measuring 0.6 to 1.5 μm long, and 0.5 to 0.7 μm wide, do not have a capsule, do not form spores, and are aerobic. On blood or
chocolate agar, colonies are small (~0.5-2 mm after 48-72 hours), convex, non-hemolytic and non-pigmented. Often
B. canis colonies can present themselves as rough variants, a reflection of their naturally rough lipopolysaccharide (
LPS) phenotype. The optimal growth temperature for
B. canis is 37°C, but growth is still possible within the range from 20°C to 40°C. Additionally, the pH range in which
B. canis grows most effectively is from pH 6.6-7.4, making this organism neutrophilic in nature. Importantly,
B. canis is a "natural rough"
Brucella. Its
Lipopolysaccharide lacks the O-polysaccharide that is present in smooth strains; an envelope trait that influences colony phenotype and host interaction without implying
a-virulence.
B. canis is also unique from other
Brucella species in that they demonstrate a distinctive phospholipid arrangement that differ greatly from other Gram-negative bacteria. Their envelope incorporates uncommon lipid species such as altered
phosphatidylethanolamine and
lipid A derivatives enriched with long-chain and branched fatty acids; features that reflect evolutionary adaptation to an intracellular lifecycle. Additionally, its phospholipid portion is mainly composed of
cis-vaccenic cyclopropane with small amounts of
lactobaccilic acid. This differs from other
Brucella species, as they demonstrate the opposite composition, with lactobacillic acid making up the majority of the phospholipid fraction.
Brucella is unusual in this composition because lactobacillic acid is typically within Gram-positive organisms but not common within Gram-negative organisms such as
Brucella. These specific envelope features are discussed alongside the organisms hallmark intracellular cycle. After uptake,
Brucella replicate within
ER-derived Brucella containing vacuoles, a niche specific to replication and survival within
B. canis.
Identification B. canis is a
zoonotic organism. The bacteria are
oxidase,
catalase and
urease positive and non-motile. Unlike
haemophilus, which they resemble, they have no requirements for added X (
hemin) and V (
nicotinamide adenine dinucleotide) factors in cultures. Full identification is established by
serology and
PCR. Due to
B. canis being naturally rough (lacking O-polysaccharide), smooth-antigen serology is unreliable. Modern practice uses
B. canis-adapated serological assays such as RSAT/2-ME, IFAT (
Immunofluorescence Antibody test) and
ELISA to make full identification.
B. canis is not acid-fast, but they tend to maintain their color when exposed to weak acids. This results in their red color when stained. When isolated,
B. canis is always in a rough form, with hydrophobic LPS imbedded in its outer membrane.
MALDI-TOF mass spectrometry with validated databases and whole-genome sequencing (WGS) are now increasingly used for definitive confirmation of
B. canis and specific outbreak tracing. Colonies of
Brucella can typically start to be seen after 48 hours. These colonies tend to be 0.5-1.0 mm in diameter, with a convex shape and are typically circular. Growth is often slower than other bacteria, with colonies requiring up to 72 hours for clear visualization.
B. canis also possesses a complete tricarboxylic acid (TCA) cycle, which primarily utilizes oxygen as its terminal electron acceptor within its electron transport chain. In anaerobic conditions, nitrate can also function as a terminal electron acceptor because
B. canis is capable of producing nitrate reductase.
B. canis also exhibits strong urease activity, producing the enzyme urease to hydrolyze urea into ammonia and carbon dioxide. This enzymatic activity is relevant for its role in nitrogen acquisition and as a notable virulence factor, as it helps to neutralize and facilitate survival within surrounding acidic environments. For laboratory identification, a relevant metabolic characteristic of
B. canis is that it does not require supplemental for growth, unlike some other
Brucella species. Additionally,
B. canis has demonstrated growth on media containing thionine, but no growth on media containing basic fuchsin.
Genome B. canis has two distinct circular chromosomes, a structure conserved across the
Brucella genus. For the reference strain ATCC 23365, Chromosome 1 has 2,199 genes, and Chromosome 2 has 1,224 genes. These two circular chromosomes contain multiple distinct shared regions, which can be attributed to horizontal gene transfer. Despite this significant similarity, it is still possible to differentiate between
B. canis and
B. suis using PCR assays targeting specific known genetic variations. The most notable distinguishing factor is the lack of O-polysaccharide in its lipopolysaccharide, causing the naturally "rough" phenotype for
B. canis in contrast to
B. suis which retains the naturally "smooth" phenotype. ==Pathogenicity ==