Actinomycetes and Propionibacterium

1. Actinomycetes and Propionibacterium (Those that form filaments)

2. 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

3. 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

4. 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

5. 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

6. Granules

7. 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

8. Nocardia acid fast stain

9. 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.

10. 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

11. 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.

12. Propionibacterium

13. 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

14. 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

15. Propionibacterium • Antibiotic susceptibility/treatment • Tetracycline • Acutane – inhibits sebum formation and is only used in severe cases of acne because there are many side effects.