1. Aerobic Actinomycetes and Anaerobic Actinomyces

2. Taxonomy of the Aerobic Actinomycetes
Gram-positive branching filaments that sporulate or fragment: the aerobic
Actinomycetes (order Actinomycetales)
Aerobic Actinomycetes whose cell walls contain mycolic acid: Nocardia species and Rhodococcus species (family Nocardiaceae)
Aerobic Actinomycetes whose cell walls lack mycolic acid: Streptomyces species

3. Taxonomy of the Anaerobic Actinomyces
Anaerobic non-sporulating gram-positive rods consist of two groups based on guanosine (G) plus cytosine (C) DNA content: Low mole percent (30-53%) and high mole percent (49-68%)
Actinomyces species member of the high G+C group

4. Taxonomy of the Aerobic Actinomycetes: Pathogenic Genera
Nocardia
Actinomadura
Streptomyces
Rhodococcus
Gordonia
Tsukamurella
Tropheryma whipplei (Non-cultivable)

5. Aerobic Actinomycetes: Natural Habitats
Nocardia species and other aerobic
Actinomycetes ubiquitous in soil and primarily responsible for decomposition of organic plant matter
Rhodococcus species present in the intestinal bacterial flora of grazing herbivores especially horses
Streptomyces species (>3,000) widely distributed in soil

6. Anaerobic Actinomyces: Natural Habitats
Anaerobic Actinomyces species
are normal inhabitants of the
mucous membranes of humans
and animals

7. Aerobic Actinomycetes: Modes of Infection
Nocardia infection acquired by inhalation of or direct skin inoculation (traumatic) by environmental organisms
Rhodococcus infection due primarily to inhalation of organisms by animal handlers (horses, pigs, cattle)
Streptomyces are soil organisms that can infect traumatic wounds especially of the feet

8. Aerobic Actinomycetes: Modes of Infection
Actinomadura species (A. madurae, A. latina, A. pelletieri) produce subcutaneous infections in tropical and subtropical countries with those who walk barefooted
Gordonia and Tsukamurella species are closely related to Rhodococcus, and are soil organisms considered opportunistic pathogens

9. Anaerobic Actinomyces: Modes of Infection
Actinomyces invades normally
sterile tissue from endogenous
mucous membrane sites of
normal colonization

10. Aerobic Actinomycetes: Types of Infectious Disease
Nocardia a facultative intracellular parasite that infects human macrophages and inhibits the fusion of phagosomes containing organisms with lysosomes.
Nocardia infections generally occur in immunocompromised patients or those with underlying pulmonary disease

11. Aerobic Actinomycetes: Types of Infectious Disease
Nocardia asteroides complex: N. asteroides sensu stricto type VI, N. abscessus, N. farcinica, and N. nova, major cause of pulmonary infection
N. otitidiscavarium infrequent cause of systemic infection
N. brasiliensis inoculated into subcutaneous tissue of foot produces actinomycotic mycetomas

12. Aerobic Actinomycetes: Types of Infectious Disease
Nocardial pneumonia occurs primarily in immunocompromised hosts and produces necrotizing pyogranuloma formation.
Extrapulmonary dissemination (~50%) and metastatic brain abscess (~30%) complications of nocardial pneumonia.
Actinomycotic mycetoma (pyogenic subcutaneous infection) causes local tissue destruction including bone

13. Aerobic Actinomycetes: Types of Infectious Disease
Rhodococcus equi infects macrophages inhibiting phagolysosome fusion, and produces pulmonary disease with cavitation. Infection occurs in immunocompromised (especially HIV-infected) individuals who handle horses.
R. equi disseminates to other organs including the brain and subcutaneous tissue

14. Aerobic Actinomycetes: Types of Infectious Disease
Streptomyces (S. anulatus formerly S. griseus, and S. somaliensis) associated with actinomycotic mycetoma in warm climates.
S. somaliensis a frequent cause of actinomycotic mycetomas of the head and neck.

15. Aerobic Actinomycetes: Types of Infectious Disease
Whipple’s disease: diarrhea, weight loss, lymphadenopathy, fever, and arthralgia
Typical histopathology is presence of PAS-positive foamy macrophages infiltrating the lamina propria of the small intestine
Caused by intracellular infection of macrophages by Tropheryma whipplei (non-cultivable, diagnosis by typical histopathology combined with PCR)

16. Anaerobic Actinomyces: Types of Infectious Disease
Actinomyces israelii causes actinomycosis in which chronic granulomas become suppurative. Cervicofacial actinomycosis most common (~60%), followed by abdominal (20%) and pulmonary (15%).
Tissue pus contains sulfur granules, a tangled mass of branching bacteria. Presence of sulfur granules establishes a diagnosis of actinomycosis.

20. Aerobic Actinomycetes: Identification
Nocardia and Rhodococcus (potentially pathogenic) and Streptomyces (less frequently pathogenic) obligate aerobes
Nocardia asteroides complex organisms thin ( m) filaments up to 20 m in length demonstrating beaded gram-positivity
Rhodococcus equi gram-positive coccobacilli

21. Aerobic Actinomycetes: Identification
Nocardia grows in a variety of media including blood and chocolate agars, Sabouraud’s dextrose agar without chloramphenicol, Lowenstein-Jensen slant, Middlebrook agar, and thioglycolate or trypticase soy broth.
Growth is slow requiring 5-7 days up to 3 weeks for colony formation at 25o to 37oC.
Growth in culture of Actinomadura and Streptomyces similar to Nocardia

25. Aerobic Actinomycetes: Identification
Nocardia and Rhodococcus are partially acid-fast positive by modified Kinyoun stain (1% H2SO4 used as decolorizing agent)
Resistance or sensitivity of growth in glycerol broth to lysozyme
Urease activity
Decomposition of the substrates casein, tyrosine, xanthine, and hypoxanthine

28. Aerobic Actinomycetes: Identification
Lysozyme Urease2
Nocardia asteroides
N. brasilensis
N. otitidiscavarium
Streptomyces anulatus – /–
S. somaliensis – –
Actinomadura madura – –
A. pelletieri – –
1Resistance of growth in glyercol broth to lysozyme
2Christensen urea slant

29. Aerobic Actinomycetes: Decomposition of Substrates
Cas Tyr Xan Hyp
Nocardia asteroides – – – –
N. brasilensis –
N. otitidiscavarium – –
Strepomyces anulatus NR2
S. somaliensis –
Actinomadura madura –
A. pelletieri –
1Susceptibility testing required, N. farcinica characteristically resistant to cefotaxime, and demonstrates variable resistance to ceftriaxone.
2NR = not reported.
3A. madura esculin decomposition positive, A. pelletieri esculin decomposition negative.

30. Antimicrobial Susceptibility1 of Nocardia asteroides complex (% Susceptible)
Sul Cip Ami Cef Ctr Imi
N. asteroides
N. farcinica
N. nova
1Sul=sulfamethoxazole,Cip=ciprofloxacin,Ami=amikacin, Cef=cefotaxime,Ctr=ceftriaxone,Imi=imipenem
2Nocardia asteroides sensu stricto type VI
Sorrell, T.C., Mitchell, D.H., and Iredell, J.R.. Chapter Nocardia
species. In Mandell, Douglas, and Bennett’s Principles and Practice of
Infectious Dieseses. G.L. Mandell, J.E. Bennett, R. Dolin, Eds. Elsevier
Churchill Livinstone, 2005.

31. Aerobic Actinomycetes: Identification
Rhodococcus, Gordonia, and Tsukamurella difficult to characterize biochemically with identification based on partial acid-fastness, colony morphology, and 16S rRNA gene sequence analysis
Rhodococcus: slimy, salmon-pink colonies
Gordonia: smooth, beige to salmon-pink colonies
Tsukamurella: cerebroid, cream colonies

32. Anaerobic Actinomyces: Identification
Actinomyces israelii anaerobic with clinical strains varying from obligate anaerobes to microaerophilic
A. israelii definitively identified by detection using gas liquid chromato- graphy (GLC) of acetic and lactic acid as end products of carbohydrate metabolism

33. Recommended Reading Winn, W., Jr., Allen, S., Janda, W., Koneman,
E., Procop, G., Schreckenberger, P., Woods, G.
Koneman’s Color Atlas and Textbook of
Diagnostic Microbiology, Sixth Edition,
Lippincott Williams & Wilkins, 2006:
Chapter 15. Aerobic Actinomycetes
Chapter 16. The Anaerobic Bacteria

34. Recommended Reading
Murray, P., Baron, E., Jorgensen, J., Landry, M., Pfaller, M.
Manual of Clinical Microbiology, 9th Edition, ASM Press,
2007:
Conville, P.S., and Witebsky, F.G. Chapter 35. Nocardia, Rhodococcus, Gordonia, Actinomadura, Streptomyces, and Other Aerobic Actinomycetes
Koenoenen, E., and Wade, W.G. Chapter 56. Propionibacterium, Lactobacillus, Actinomyces, and Other Non-Spore-Forming Anaerobic Gram-Positive Rods