Pasteurella canis

Nomenclature

“Micrococcus gallicidus” was the first scientific name used for these bacteria. For a short time, the bacteria were unofficially placed in different genera, such as Octopsis, Coccobacillus, and Eucystia. In 1887, genus “Pasteurella” was proposed to honor Louis Pasteur for his critical discoveries in the field of microbiology.

Before molecular technology was available, species were often labeled based on staining and the hosts from where species were isolated. Until 1932, the genus Pasteurella only consisted of the species type Pasteurella multocida. Pasteurella canis sp. nov. was previously classified as P. multocida biotype 6 or “dog-type” strains. In 1985, Pasteurella underwent taxonomic reclassification based on DNA hybridization, resulting in several subspecies of P. multocida and new Pasteurella species, including P. canis.

Pasteurella canis includes two biotypes: biovar 1 originated from canines, whereas biovar 2 originated from bovines. The two biotypes are distinguishable from an indole test: biovar 1 is indole positive whereas biovar 2 is indole negative.

Microbiology

Pasteurella canis is a Gram-negative coccobacillus that shows bipolar staining. It is also nonhaemolytic and nonmotile.

Pasteurella canis is reported as aerobic and facultative anaerobic in different sources. It metabolizes both glucose and sucrose. It can also be indole positive or negative depending on the biotype.

Molecular typing

Molecular analysis of the genome has become the popular method to identify bacteria. The genome of P. canis has yet to be fully sequenced, but several genes and their sequences were already identified. Among them, 16S rRNA, 23S rRNA, RNA polymerase subunit B (rpoB), and manganese-dependent superoxide dismutase (sodA) are used to study Pasteurella phylogeny. However, molecular and biochemical analyses often show conflicting results. For example, research has suggested some P. canis strains were in fact members of P. multocida based on DNA analysis.

Disease

Pasteurella canis is an opportunistic pathogen that can infect both animals and humans.

Animal infections

Pasteurella canis can be found in healthy domesticated, farm-raised, and wild animals, such as dogs, cats, rabbits, horses, sheep, cattle, ferrets, deer, and even California sea lions. The bacteria are normally isolated from the oral cavities and respiratory tracts of these animals. P. canis biotype 1 was shown to secrete a toxin analogous to P. multocida toxin, but its identity is unknown. P. canis is responsible for a number of canine infections, including systemic infection, external otitis, bacterial rhinitis, vertebral osteomyelitis, meningomyelitis (a type of myelitis), bronchopneumonia, tracheitis, paranasal sinus inflammation, and toxicosis. Horses infected with the bacteria may develop arthritis. The bacteria also cause pneumonia in cattle and various infections in sheep, cats, rabbits, and deer.

Human infections

Pasteurella canis usually does not affect humans but may be transmitted from animals to humans through animal bites, scratches, or licking over wounds. In one case, a patient exposed to rabbit secretions was infected with P. canis. Those with rheumatoid arthritis, cirrhosis, and diabetes mellitus are more susceptible to the bacteria. Patients who are immunocompromised also have higher risk of infections.

Pasteurella canis often causes soft-tissue infections and wound infections, as well as systemic bacteremia in humans. Joint prosthetics can also be infected by the bacteria. Less commonly, this bacterium may result in respiratory infections, septic arthritis, endocarditis, and meningitis. Most patients with pulmonary infections caused by this species are elderly with pre-existing chronic lung diseases such as COPD.

Antibiotics treatment and resistance

Many common antibiotics can successfully treat P. canis infections in both humans and animals. P. canis has shown sensitivity to ampicillin (penicillin), cefuroxime (second-generation cephalosporin), most third-generation cephalosporins (cefixime, cefotaxime, ceftriaxone, and cefoperazone), ciprofloxacin (quinolones), trimethoprim/sulfamethoxazole (sulfonamides), chloramphenicol, most aminoglycosides, and tetracycline. However, the bacterium is also resistant to numerous drugs, such as dicloxacillin (penicillin), some aminoglycosides (spectinomycin and neomycin), vancomycin (glycopeptides), cephalexin and cefadoxil (first-generation cephalosporin), erythromycin (macrolides), and imipenem (carbapenem).

References

References

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