Actinomycetes and Propionibacterium

(Those that form filaments)

Actinomycetes

Classification Order – Actinomycetales

Show fungus-like characteristics such as branching in tissues or in culture (look like mycelia).

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

The anaerobic genera: Actinomyces, Arachnia, and Bifidobacterium

Morphology and cultural characteristics 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.

Biochemistry ID by gas liquid chromatography (GLC) of metabolic by-

products or fluorescent antibody studies

Actinomycetes

Clinical significance 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.

This is rare today because of prophylactic antibiotic therapy.

May cause thoracic or abdominal infections May cause meningitis, endocarditis, or genital

infections

Actinomycetes

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 Penicillin

Granules

Actinomycetes

The aerobic genera: Nocardia, Actinomadura, and Streptomyces. There are three clinically important species of Nocardia – N. asteroides, N. brasilensis, and N. caviae

Morphology and cultural characteristics 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

Nocardia acid fast stain

Actinomycetes

Biochemistry The organisms are identified based on sugar fermentations

and hydrolysis reactions (caseine, tyrosine, etc.) Clinical significance

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.

Actinomycetes

Nocardiosis – is a localized or disseminated disease occurring after inhalation of organisms.

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

Mycetoma – aminoglycosides Nocardiosis – sulfonamides or sxt

Propionibacterium

Classification 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

Pleomorphic, small G+B, may have Chinese letter configurations or may be branching.

Propionibacterium

Propionibacterium

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 Catalase + Indole +/- Ferment glucose Produce caseinase

Propionibacterium

Virulance factors Protease

Clinical significance – Is part of skin NF Has been implicated in causing acne –

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

Antibiotic susceptibility/treatmentTetracyclineAcutane – inhibits sebum formation and is

only used in severe cases of acne because there are many side effects.