10 aerobic actinomycetes-and_anaerobic_____actinomyces_v1-_3

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Aerobic Actinomycetes and Anaerobic Actinomyces

Dr. John R. WarrenDepartment of PathologyNorthwestern University

Feinberg School of MedicineJune 2007

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

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

Taxonomy of the Aerobic Actinomycetes: Pathogenic Genera

• Nocardia

• Actinomadura

• Streptomyces

• Rhodococcus

• Gordonia

• Tsukamurella

• Tropheryma whipplei (Non-cultivable)

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

Anaerobic Actinomyces: Natural Habitats

Anaerobic Actinomyces species

are normal inhabitants of the

mucous membranes of humans

and animals

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

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

Anaerobic Actinomyces: Modes of Infection

Actinomyces invades normally

sterile tissue from endogenous

mucous membrane sites of

normal colonization

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

• 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

• 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

• 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

• 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.

• 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)

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.

Aerobic Actinomycetes: Identification

• Nocardia and Rhodococcus (potentially pathogenic) and Streptomyces (less frequently pathogenic) obligate aerobes

• Nocardia asteroides complex organisms thin (0.5-1.0 m) filaments up to 20 m in length demonstrating beaded gram-positivity

• Rhodococcus equi gram-positive coccobacilli

• 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

• 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

Aerobic Actinomycetes: Identification Lysozyme1 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

Aerobic Actinomycetes: Decomposition of Substrates

Cas Tyr Xan Hyp Nocardia asteroides1 – – – – N. brasilensis + + – + N. otitidiscavarium – – + +Strepomyces anulatus + + + NR2

S. somaliensis + + – +Actinomadura madura3 + + – +A. pelletieri3 + + – +

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.

Antimicrobial Susceptibility1 of Nocardia asteroides complex (%

Susceptible)Sul Cip Ami Cef Ctr Imi

N. asteroides2 96-99 38-98 100 94-100 94-100 77-98 N. farcinica 89-100 68-88 100 0-7 0-73 64-87N. nova 89-97 0 100 87-100 100 1001Sul=sulfamethoxazole,Cip=ciprofloxacin,Ami=amikacin,

Cef=cefotaxime,Ctr=ceftriaxone,Imi=imipenem2Nocardia asteroides sensu stricto type VI

Sorrell, T.C., Mitchell, D.H., and Iredell, J.R.. Chapter 252. Nocardia species. In Mandell, Douglas, and Bennett’s Principles and Practice ofInfectious Dieseses. G.L. Mandell, J.E. Bennett, R. Dolin, Eds. Elsevier Churchill Livinstone, 2005.

• 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

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

10 aerobic actinomycetes-and_anaerobic_____actinomyces_v1-_3

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