Capnocytophaga spp.

Capnocytophaga genus belongs to the family Flavobacteriaceae.
There are >9 species of Capnocytophaga, which can be divided into two groups – resident of human mouth flora and dog/cat mouth flora.

Species found in the human oral cavity	C. gingivalis, C. granulosa, C. haemolytica, C. leadbetteri, C. ochracea and C. sputigena
Species found in dog/cat oral cavity	C. canimorsus and C. cynodegmi

Risk factors for Capnocytophaga infection:

• Dog bite, cat-scratch
• immunocompromise state, including chemotherapy, biologics and HIV
• asplenia
• cirrhosis
• heavy alcohol use
• diabetes

Disease caused by Capnocytophaga:

• Bacteraemia
• Endocarditis, Pericarditis
• Keratitis, endophthalmitis, meningitis, intracranial abscess
• Chest infection, empyema, mediastinal abscess
• Iliopsoas abscess, peritonitis
• Osteomyelitis
• chorioamnionitis, neonatal sepsis. etc.

C canimorsus infection may result in septic shock, fever, disseminated purpura/purpura fulminans, acute renal failure, and confusion.

Pathogenesis:

Capnocytophaga can evade the immune system, at least at the early stages of infection. These properties have been observed in various strains –

• Failure to interact with toll-like receptor 4,
• Prevent the development of inflammatory responses and
• Resistance to complement-mediated killing and phagocytosis by polymorphonuclear cells.

Laboratory identification

• Slow-growing, capnophilic, facultative anaerobe.
• Grow on blood and chocolate agar but not MacConkey agar.
• Thin, long, often fusiform Gram-negative rod. However, it could be pleomorphic in old cultures.
• Oxidase +ve, Catalase +ve, indole -ve, urease -ve,
• Identification confirmation – 16S rRNA, MALDI-ToF

Antimicrobial susceptibility:

Capnocytophaga spp produces various beta-lactamases – TEM-17, CSP-1, CfxA, conferring resistance to penicillins, cephalosporins, aztreonam and monobactams.

Beta-lactamase production is rare in C canimorsus.

Betalactam-betalactamse combinations (pip-tazobactam, coamoxiclav), and carbapenems are active.

Antibiotics that are active	Betalactam-betalactamse combinations (pip-tazobactam, coamoxiclav), Carbapenems, Clindamycin, Linezolid, Doxycycline, Chloramphenicol
Antibiotics not active	Polymyxin, Fusidic acid, Fosfomycin, Colomycin, Trimethoprim
Antibiotic with variable activity	Erythromycin, Rifampicin, Quinolone, Cephalosporins, Metronidazole, Vancomycin, Aminoglycoside, Aztreonam.