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Arcanobacterium haemolyticum is a bacterium
responsible for cases of both pharyngitis and cutaneous infections
but has also been identified infrequently as a cause of various types
of invasive disease.
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This pleomorphic, nonsporulating, hemolytic gram-positive (sometimes
gram variable) bacillus grows like Corynebacterium diphtheriae on
Loeffler medium but grows poorly on tellurite media. Optimal growth
is achieved on either human or rabbit blood agar, but the organism
will slowly grow on standard blood agar plates. This organism was
formerly classified as Corynebacterium haemolyticum. The
bacterium typically has a black opaque dot in the center of each
colony. A haemolyticum can liberate toxins, including
a dermonecrotic toxin, using a mechanism similar to that for the
production of erythrogenic toxin by group A streptococci (GAS).1
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Humans are the primary reservoir of A haemolyticum,2,3 but
the organism is rarely recovered from healthy individuals.4 Peak
age of illness is in the second decade of life,5 whereas
GAS, which may cause a similar presentation, peaks in the first
decade of life. No seasonal variation occurs. A haemolyticum is responsible
for 0.5% to 2.5% of bacterial pharyngitis cases
in the United States.3,6Disease is spread from
person to person presumably by respiratory droplet, although the mechanism
of spread has yet to be completely determined. The incubation period
is unknown.
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The mechanism for adherence of this organism to pharyngeal mucosa
is unknown. Experimentally, Arcanobacterium can
invade certain types of cells and survive.7 Similar
to group A streptococci, an exotoxin is likely the cause of rash
with this organism.
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Clinical Manifestations
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Presentation of disease caused by A haemolyticum is
similar to GAS pharyngitis with fever, pharyngeal exudate, and lymphadenopathy,
but palatal petechiae and a strawberry tongue are usually absent.1,3,8 In
up to 50% of cases, a rash is present; usually maculopapular,
but may be scarlatiniform.3 The rash begins peripherally
on extensor surfaces of the extremities and spreads centrally sparing
the face, palms, and soles. The rash typically starts 1 to 4 days
after symptoms of the sore throat begin. Occasionally pruritic,
the rash persists for over 2 days in the majority of patients.
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Skin infections, especially chronic ulceration, caused by A
haemolyticum occur mainly in tropical countries. Invasive
infections, including sepsis, brain abscess, meningitis, osteomyelitis,
and pneumonia have been reported.3,9,10
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Adolescents and young adults complaining of sore throat and found
to have a rash should be suspect. Isolation of A haemolyticum from
a clinical specimen is diagnostic. Growth of the Arcanobacterium is
facilitated by culture using human or rabbit blood-agar and incubating the
plates for 24 to 48 hours at 37°C with 5% carbon dioxide.1Microbiology
kits designed to help identify A haemolyticum have
been developed11 but are not generally available
in most clinical laboratories. ...