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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?
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