Capnocytophaga Species

Capnocytophaga is a genus in the family Flavobacteriaceae encompassing a group of slow-growing, capnophilic (carbon dioxide−loving), facultative anaerobic, gram-negative fusiform bacilli. Species are divided into two groups, the “human” group (formerly classified as Centers for Disease Control and Prevention [CDC] biogroup dysgenic fermenter [DF]-1), which colonize the oral cavity of humans and 4 species in the zoonotic group (CDC biogroup DF-2), which are distinguishable from human Capnocytophaga because they are catalase positive and generally oxidase positive and colonize the oral cavity of dogs and cats. These two groups are considered separately because the patient population, epidemiology, and clinical features of infection are distinct.

Diagnosis of infection typically is made by isolating Capnocytophaga in culture , a procedure that requires incubation in an environment with enhanced carbon dioxide concentration under aerobic or anaerobic conditions. In blood cultures, growth may be detected first in the anaerobic bottle, and blind subculture on enriched media may be needed because of inhibition of growth in the presence of sodium polyanethol sulfonate. Colonies are detectable after 2–4 days or longer incubation on several media, including blood agar; growth does not occur on MacConkey agar. Generally, species in this genus ferment carbohydrates, except mannitol and xylose. Identification by conventional tests frequently is not successful. Species can be identified by matrix-assisted laser desorption ionization−time of flight (MALDI-TOF) spectrometry, DNA hybridization, 16S rRNA PCR, restriction fragment length polymorphism analysis, or 16S rRNA gene sequencing. ^, Whole-genome next-generation sequencing on plasma and broad spectrum PCR have been used to directly detect C. canimorsus in blood and cerebrospinal fluid (CSF), respectively.