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Introduction | Methods | Discussion | References
The third case report, which is the first in Australia, of human infection with Neisseria canis is documented. This is the first case report in which the pathogenicity of this organism for humans is unequivocally demonstrated. Commun Dis Intell 1999;23:221.
IntroductionNeisseria canis (N. canis) was first described by Berger in 1962.1 The bacterium's normal habitat is the throat of the cat and dog. It is regarded as a true Neisseria with phenotypic properties that allow its recognition as a distinct species.2,3 Only two previous case reports of human infection have been found by the authors.4,5 The first case of human infection with N. canis was published by Hoke and Vedros4 in 1982. This isolate came from a cat bite wound on a child. No other clinical details were described. In 1989 N. canis was reported in a mixed culture that included Pasturella multocida (P. multocida) and Eiknella corrodens from a cat bite wound on the arm of a previously healthy 36 year old woman. The wound was inflamed and the patient was successfully treated with amoxycillin. P. multocida was regarded as the primary pathogen in this case.5
Clinical featuresThe patient, a 50 year old male normally in good health, presented with a purulent wound to the sole of his foot, with surrounding cellulitis. The patient recalled having trod on a dog bone a few days previously. A swab for culture was taken and antibiotics commenced (metronidazole and amoxycillin/clavulanic acid). Seven days later he made a complete recovery apart from some residual induration.
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Laboratory diagnosisStandard bacteriologic techniques as outlined in the Manual of Clinical Microbiology6 were used. The Gram stain showed moderate numbers of polymorphs. A moderate pure growth of a small gram negative coccus was obtained on aerobic blood agar, with the formation of yellowish non-haemolytic, 2 - 4 mm slightly flat topped colonies after 48 hours. It grew well on nutrient agar but did not grow on MacConkey agar. The organism was a facultative anaerobe, non-capnophilic and growth at 37oC was better than at 30oC or 42oC. The remainder of the diagnostic tests were consistent with the identification of N. canis, and it was sensitive to benzylpenicillin, erythromycin, and tetracycline but resistant to vancomycin.
A conserved segment (441 base pairs) of the isolate's RNA was subject to molecular studies, using BLAST analysis with the GeneBank7 data bank. A significant similarity was found with a sequence of 422 matching base pairs (95%) with GenBank Accession number L06170 - Neisseria canis ATCC 14687.
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DiscussionIt is considered without doubt that N. canis was pathogenic. Currently the organism is a very rare isolate associated with cat or dog contact, but it may be under reported. The laboratory diagnostic clues are the isolation of an oxidase positive, gram negative, non-fastidious coccus that is very strongly catalase positive and forms dull yellow flat-topped non-haemolytic colonies on Day 2. It is nitrate positive but otherwise essentially asaccharolytic and rather inert in its biochemical reactions. It is described in the literature as galactosidase negative, tributyrin hydrolysis negative, DN'ase negative, nitrite negative and polysaccharide synthesis negative.3,6 Currently there is no reason to suspect that the organism would not be covered by the current Australian Antibiotic Guidelines8 for the management of animal bites.
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References1. Berger U. Uber das vorkommen von neissien bei einigen. Tieren. Z Hyg 1962;148:445-57.
2. Weyant RS, et al. Identification of unusual pathogenic gram- negative aerobic and facultatively anaerobic bacteria. 2nd Ed. Baltimore: Williams and Wilkins, 1995.
3. Krieg NR, Hold JG (Eds). Bergey's manual of systematic bacteriology, Vol 1. Baltimore: Williams and Wilkins, 1984.
4. Hoke C, Vedros NA. Characterization of atypical aerobic gram-negative cocci isolated from humans. J Clin Microbiol 1982;15:906-14.
5. Guibourdenche M, Lambert T, Riou, JY. Isolation of Neisseria canis in a mixed culture from a patient after a cat bite. J Clin Microbiol 1982;27:1673-74.
6. Murray PR (ed). Manual of Clinical Microbiology. 6th Ed. Washington: ASM Press, 1995.
7. Benson DA, et al Nucleic Acids Res 26:1-7.
8. Therapeutic Guidelines Antibiotic, 10th Ed. 1998-1999. Therapeutic Guidelines Limited, Melbourne, 1998.
Author affilliations1. Sullivan and Nicolaides and Partners Pathology, Lismore, New South Wales
2. General Practitioner, Evans Head, New South Wales
This article was published in Communicable Diseases Intelligence Volume 23, No 8, 5 August 1999.