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Actinomycetes and
Propionibacterium
(Those that form filaments)
Actinomycetes
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Classification
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Order – Actinomycetales
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Show fungus-like characteristics such as branching in
tissues or in culture (look like mycelia).
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The filaments frequently segment during growth to produce
pleomorphic, diphtheroidal, or club shaped cells.
The cell wall and the internal structures are typical of
bacteria rather than fungi.
Some are aerobic and others are anaerobic.
All are slow growing
Actinomycetes
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The anaerobic genera: Actinomyces, Arachnia, and
Bifidobacterium
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Morphology and cultural characteristics
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G+ branching, or diphtheroid-like bacilli
Anaerobic and require CO2 for growth
Non-sporing
Will grow on anaerobic BA or PEA.
A. israelii, the most commonly isolated species,
produces rough, granular colonies that resemble
molars.
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Biochemistry
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ID by gas liquid chromatography (GLC) of metabolic byproducts or fluorescent antibody studies
Actinomycetes
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Clinical significance
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Are part of the NF found in the cavities of humans and
other animals.
All may cause actinomycosis or “lumpy jaw” which is a
cervicofacial infection that used to occur following
tooth extractions or dental surgery which provided
traumatized tissue for growth of the microorganism
which may also invade the bone.
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This is rare today because of prophylactic
antibiotic therapy.
May cause thoracic or abdominal infections
May cause meningitis, endocarditis, or genital
infections
Actinomycetes
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Every kind of infection is characterized by draining
sinuses, usually containing characteristic granules
which are colonies of bacteria that look like dense
rosettes of club-shaped filaments in radial
arrangement
Treatment
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Penicillin
Granules
Actinomycetes
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The aerobic genera: Nocardia, Actinomadura, and
Streptomyces. There are three clinically important
species of Nocardia – N. asteroides, N. brasilensis,
and N. caviae
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Morphology and cultural characteristics
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G+ branching bacillus that may fragment to bacillary or
coccoid forms
Aerobic
Specimens should be inoculated onto 7H10 agar or
Lowenstein-Jensen agar and brain heart infusion agar.
Colonies produced are typically orange, dry, crumbly,
and adherent.
The organisms are weakly acid fast or non acid fast
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Nocardia acid fast stain
Actinomycetes
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Biochemistry
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The organisms are identified based on sugar fermentations
and hydrolysis reactions (caseine, tyrosine, etc.)
Clinical significance
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Mycetoma – organism enters the body through breaks in the
skin and causes a localized infection involving skin,
cutaneous, and subcutaneous tissue.
The three most characteristic features seen are
swelling, draining sinuses and granules.
This disease can also be caused by fungi as well as
Nocardia, Actinomadura, and Streptomyces.
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Actinomycetes
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Nocardiosis – is a localized or disseminated disease
occurring after inhalation of organisms.
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Pulmonary infections resemble tuberculosis and
can remain confined to the lungs or may
disseminate, with a predilection for the brain and
meninges.
 The disease is characterized by multiple confluent
abscesses and intense suppuration.
 It is usually a disease of compromised hosts.
Antimicrobic susceptibility/treatment
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Mycetoma – aminoglycosides
Nocardiosis – sulfonamides or sxt
Propionibacterium
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Classification
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Two species P. acnes and P. granulosum.
Are described as anaerobic diphtheroids, though
some can grow in CO2.
Most clinical isolates are P. acnes which is part of
the NF of skin.
Morphology and cultural characteristics
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Pleomorphic, small G+B, may have Chinese letter
configurations or may be branching.
Propionibacterium
Propionibacterium
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Grow well on CBA, producing tiny translucent to
opaque and white to gray colonies.
Growth may be slow.
Anaerobic, though occasional strains of P.
granulosum grow in CO2
Biochemistry
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Catalase +
Indole +/Ferment glucose
Produce caseinase
Propionibacterium
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Virulance factors
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Protease
Clinical significance –
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Is part of skin NF
Has been implicated in causing acne –
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During adolescence more sebum is produced, and P.
acnes metabolizes it to produce fatty acids.
These may contribute to the inflammatory response seen
in acne.
Has also been isolated from joint infections
Propionibacterium
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Antibiotic susceptibility/treatment
Tetracycline
 Acutane – inhibits sebum formation and is
only used in severe cases of acne because
there are many side effects.
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