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September/October 2001
Presented by: Dr. K.N. Brown and Dr. R.S Roman
A 68 year-old man attended his family practitioner two days after
having been bitten on the thumb by his dog. He felt extremely debilitated
and was suffering from intermittent chills. On examination, he had
a fever and appeared to be very ill. Only a small, apparently almost
completely healed lesion was present on his thumb.
The phyisician ordered blood cultures over the next three days.
Three of the four bottles inoculated yielded microorganisms, which
on gram-stain showed small slender gram-negative, slightly curved
rods with pointed ends. The fourth bottle, which was anaerobic,
failed to grow any organisms.
On subcultures to blood agar, small non-haemolytic colonies were
evident in 24 hours. The organism was very slow growing but produced
colonies 2-3 mm. in diameter after 3 days. The colonies were relatively
flat with slightly irregular edges displaying spreading growth.
Growth was augmented by incubation in carbon-dioxide, but was also
seen anaerobically. Growth did not occur on MacConkey agar. The
organism was oxidase and catalase positive. It failed to produce
any biochemical change when submitted to API testing.
Testing showed the organism to be beta-lactamase begative, but because
of its slow growth, disc-diffusion susceptibility testing took three
days to perform despite using a heavy inoculum on the test plates.
Whilst, in the strict sense, uncontrolled, these susceptibility
tests suggested that the organism was resistant to gentamicin and
trimethoprim/sulphamethoxazole, but was sensitive to the penicillins,
cephalosporins, ciprofloxacin, erythromycin and clindamycin.
The organism was referred to a reference laboratory which confirmed
the impressions formed in our own facility.
The patient was treated with oral ampicillin. He was clinically
imporved two days later and appeared to be completely recovered
a week later.
- What genus of organisms is likely implicated in this man's
bacteremia?
- What specific member of this genus is most likely involved?
- Apart from a dog bite, what other animal could result in a
bacteremia from this genus of organisms?
- Would cloxacillin be a useful drug to use in an infection
with this organism?
- What particular group of patients are at increased risk of
mortality when infected with this organism?
This case is an illustration of bacteremia due to Capnocytophaga
canimorsus originating from a dog bite. Capnocytophaga
spp. includes C. gingivalis, C. granulosa, C. haemolytica, C.
ochracea and C. sputigena, which are members of the
human oral flora. Other Capnocytophaga species include
C. canimorsus and C. cynodegmi, which colonize
the oral cavities of cats and dogs. C. canimorsus was previously
called CDC group dysgonic fermenter-2 or CDC group DF-2.
Capnocytophaga spp. are thin, spindle-shaped, gram negative
rods 1-3 mm in length and therefore morphologically resemble Fusobacterium
spp. Curved filaments and coccoid forms can also be seen. Movement
of the organism under the microscope has been described as 'gliding
motility', although most do not have flagella. The organisms grow
best at 35-37ºC. Some isolates will grow better anaerobically
on primary isolation, but they are best described as capnophilic
(grows better in CO2 enriched atmosphere). They are slowing growing,
with very small colonies on blood agar after 1 day of incubation
and reaching 2-3 mm in size only after 2 to 4 days. Colonial morphology
is quite pleomorphic ranging from small discrete colonies to larger
flat colonies with irregular finger-like projections spreading from
the edges representing 'gliding motility'. The organisms do not
grow on MacConkey agar. Colonies are non-hemolytic and often have
a yellowish-orange pigment.
Clues to the identification of Capnocytophaga spp. include
the characteristic gram stain, colonial morphology and growth requirements.
They may be identified with some commercially available anaerobic
identification systems. Capnocytophaga species that colonize
animals (C. canimorsus and C. cynodegmi) are oxidase
positive and catalase positive, while the species colonizing the
oral cavities of humans (C. gingivalis, C. granulosa, C. haemolytica,
C. ochracea and C. sputigena) are oxidase negative
and catalase negative. It can be difficult to differentiate C.
canimorsus and C. cynodegmi with routine phenotypic
testing.
C. canimorsus and C. cynodegmi can cause infectious
complications in humans after animal bites. C. cynodegmi
causes localized wound infections, while C. canimorsus
can cause severe infections with septicemia. Predisposing factors
for severe infection include splenectomy, alcoholism, steroid medication
and other immunocompromising factors. Eighty percent of patients
with fulminant C. canimorsus infections have an underlying
predisposing medical condition. Fulminant illness can include bacteremia,
endocarditis, meningitis, shock, renal failure and peripheral gangrene.
Fulminant C. canimorsus infection has a 25% mortality
rate. Seventy-five percent of cases involve exposure to a dog, through
either ownership or a bite. C. canimorsus is carried in
the oropharynx of 25% of dogs and 15% of cats.
There are no NCCLS guidelines to interpret disk diffusion susceptibility
test results. The organism does not grow well in broth media precluding
the use of broth dilution techniques. Antibiotics expected to be
active against Capnocytophaga spp. include clindamycin,
quinolones, and the expanded spectrum cephalosporins. Activity of
the first generation cephalosporins, aminoglycosides and metronidazole
is variable. They are generally resistant to cloxacillin. Most strains
are still susceptible to penicillin, although recently the prevalence
of beta-lactamase producing isolates is increasing. Because penicillin
is often used as the empiric therapy of choice in possible infections
due to Capnocytophaga spp., testing for beta-lactamase
production should be performed in the laboratory. Testing for beta-lactamase
production has been shown to be predictive of penicillin resistance,
but it does not correlate with resistance to other beta-lactam antibiotics.
- Brenner DJ, Hollis DG, Fanning GR, et al. 1989. Capnocytophaga
canimorsus sp. nov. (formerly CDC group DF-2), a cause
of septicemia following dog bite, and C. cynodegmi
sp. nov., a cause of localized wound infection following dog
bite. J Clin Microbiol 27: 231-235.
- Mossad SB, Lichtin AE, Hall GS, Gordon SM. 1997. Diagnosis:
Capnocytophaga canimorsus septicemia. Clin Infect Dis
Feb; 24 (2): 123-267.
- Pers C, Gahrn-Hansen B, Frederiksen W. 1996. Capnocytophaga
canimorsus septicemia in Denmark, 1982-1995:review of 39
cases. Clin Infect Dis 23(1): 71-75.
- Blanche P, Bloch E, Sicard D. 1998. Capnocytophaga canimorsus
in the oral flora of dogs and cats. J Infect 36(1): 134.
- Ngaage DL, Kotidis KN, Sandoe JA, Unnikrishnan Nair R. 1999.
Do not snog the dog: infective endocarditis due to Capnocytophaga
canimorsus. Eur J Cardiothorac Surg. 16(3): 362-3.
- Jolivet-Gougeon A, Buffet A, Dupuy C, Sixou JL, et al. 2000.
In vitro susceptibilities of Capnocytophagia isolates to beta-lactam
antibiotics and beta-lactamase inhibitors. 44(11): 3186-8
- Bilgrami S, Berstrom SK, Peterson DE, et al. 1992. Capnocytophaga
bacteremia in a patient with Hodgkin's disease following bone
marrow transplantation: case report and review. Clin Infect
Dis. 14(5): 1045-1049.
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