Capnocytophaga includes bacteria previously called DF-J and DF-2 (dysgonic fermenters). Currently, the genus consists of seven species, five of which are normal flora of the oral cavity of humans. Capnocytophaga spp. resemble the HACEK organisms in their requirement for CO2 for enhanced growth and their isolation
from blood cultures. Unlike the members of the HACEK group, Capnocytophaga spp. are not as commonly involved in endocarditis as they are in septicemia in the granulocytopenic patient. Capnocytophaga spp.
are fastidious, facultatively anaerobic, gram-negative bacilli. They are thin and often fusiform (pointed ends) on Gram stain, resembling Fusobacterium spp.; FIGURE 19-21 . Growth of Capnocytophaga organisms on chocolate agar. Notice the spreading away from the center of the colony. Compare this growth to Eikenella (see Figure 19-18).
spindle shaped, coccoid, and curved filaments may also be seen.
Although flagella are usually absent, Capnocytophaga may produce gliding motility on solid surfaces. On agar,
colonies are often adherent and produce a yelloworange pigment; they can resemble colonies of E. corrodens. Most Capnocytophaga isolates are non hemolytic, except for Capnocytophaga haemo/ytica ((3-hemolytic).
Figures 19-21 and 19-22 depict the colonial and micn~ scopic morphology. Capnocytophaga ferment sucrose,
glucose, maltose, and lactose, although triple sugar iron agar (TSIA) may be negative without enrichment. They
are negative for most biochemical reactions, including indole; however, they may reduce nitrates and hydrolyze esculin.
The five normal inhabitants of the human oral cavity, Capnocytophaga ochracea (DF-l), Capnocytophaga gingivalis, Capnocytophaga sputigena, C. haemo/yticus, and Capnocytophaga granu/ose, are all oxidase and catalase negative. C. ochracea, C. gingiva lis, and C sputigena are implicated in periodontitis (Figure 19-23), while the remaining two human species have been isolated from dental plaque. Common sites of clinical isolation include blood cultures from granulocytopenic (neutropenic) patients who have oral ulcers (source of the Capnocytophaga), juvenile periodontal disease, and endocarditis.
C. ochracea is the most common clinical isolate.
Capnocytophaga canimorsus (DF-2) and Capnocytophaga cyodegmi are normal inhabitants of the oral cavity of dogs and cats and are oxidase and catalase positive. C. canimorsus can cause a fulminant, life-threatening infection in humans following a dog or cat bite or through continuous contact.
Capnocytophaga spp. are susceptible to imipenem, erythromycin, c1indamycin, tetracycline, chloramphenicol, quinolones, and (3-lactams, but they are resistant to the aminoglycosides. For C. canimorsus and C. cyodegmi infections, penicillin is the drug of choice.