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Nocardia spp.

  • Douglas I. Johnson
Chapter

Abstract

  • Genomics:
    • Nocardia asteroides: chromosome: 6,954,780 bp; 6106 predicted ORFs (Komaki et al. 2014)

    • Nocardia cyriacigeorgica GUH-2: chromosome 6,194,650 bp; 5405 predicted ORFs (Komaki et al. 2014)

    • Nocardia brasiliensis: chromosome: 9,436,348 bp; 8414 predicted ORFs (Vera-Cabrera et al. 2013)

  • Cell morphology:
    • Filamentous hypha-like cells (Fig. 23.1)

  • Gram stain:
    • Gram positive

    • “Beaded,” partially acid-fast appearance; depends on the quantity of mycolic acid in the cell wall

  • Growth:
    • Aerobes; catalase positive.

    • Found primarily in soil and water.

    • >80 species; most are rarely associated with human disease:
      • Antibiotic susceptibilities and molecular characteristics have allowed taxonomic differentiation of previous species into new complexes and clades (Brown-Elliott et al. 2006).

Genomics, Morphologies, and Growth Characteristics

  • Genomics:
    • Nocardia asteroides: chromosome: 6,954,780 bp; 6106 predicted ORFs (Komaki et al. 2014)

    • Nocardia cyriacigeorgica GUH-2: chromosome 6,194,650 bp; 5405 predicted ORFs (Komaki et al. 2014)

    • Nocardia brasiliensis: chromosome: 9,436,348 bp; 8414 predicted ORFs (Vera-Cabrera et al. 2013)

  • Cell morphology:
    • Filamentous hypha-like cells (Fig. 23.1)

  • Gram stain:
    • Gram positive

    • “Beaded,” partially acid-fast appearance; depends on the quantity of mycolic acid in the cell wall

  • Growth:
    • Aerobes; catalase positive

    • Found primarily in soil and water

    • >80 species; most are rarely associated with human disease:
      • Antibiotic susceptibilities and molecular characteristics have allowed taxonomic differentiation of previous species into new complexes and clades (Brown-Elliott et al. 2006)

Fig. 23.1

N. asteroides cells (From: PHIL #4232)

Disease States Associated with Nocardia spp.

  • Nocardiosis (Brown-Elliott et al. 2006; Wilson 2012):
    • Opportunistic pathogens and primary pathogens

    • Inhalation infections; cutaneous infections; catheter-related bacteremia

    • Pulmonary nocardiosis:
      • Opportunistic infection of immunosuppressed individuals

      • Predominantly N. asteroides; also N. cyriacigeorgica, N. brasiliensis

      • Transmission: inhalation of mycelial cells

      • Symptoms: persistent cough with purulent sputum, shortness of breath, chest pain, coughing up blood (hemoptysis), fever, night sweats, weight loss, and progressive fatigue

    • Extrapulmonary nocardiosis:
      • Hematogenous spread; CNS and cerebral nocardiosis are most common

      • Symptoms: abscess formation in the brain; headache, nausea, vomiting, neurological symptoms

    • Primary cutaneous nocardiosis:
      • Primary infection of immunocompetent individuals

      • Predominantly N. brasiliensis; also N. asteroides

      • Transmission: contact with contaminated soil

      • Produces skin abscesses and localized cellulitis; can also lead to mycetomas (Fig. 23.2)

      • Can disseminate to the lymph nodes, resulting in lymphocutaneous nocardiosis; similar to fungal sporotrichosis symptoms

    • Catheter-related bacteremia:
      • Rare but increasingly observed among immunocompromised patients

      • Associated with central venous catheter infections

Fig. 23.2

Mycetoma (From: Vera-Cabrera et al. 2013)

Virulence Factors

  • Many of the virulence factors listed below are predicted based on the genome sequencing and annotation of several Nocardia spp. (Komaki et al. 2014; Vera-Cabrera et al. 2013); experimental verification of many of their activities has yet to be determined

  • Biofilms (Al Akhrass et al. 2011):
    • Excellent biofilm former on catheters

  • Adherence to host cells and invasion:
    • Facultative intracellular pathogens (Vera-Cabrera et al. 2013)

    • Invasin:
      • Protein used to attach to host cells

      • Encoded by O3I_027570 gene

      • Similar to Yersinia pestis Inv

    • Mce proteins (mammalian cell entry):
      • 33 genes encoded in genome

      • Analogous to M. tuberculosis Mce proteins (Gioffre et al. 2005)

    • KatN and KatG (Vera-Cabrera et al. 1999):
      • Five catalase genes

      • Detoxify H2O2 in phagocytes

    • SodA (Alcendor et al. 1995):
      • Two superoxide dismutases

      • Destroys H2O2

    • Cord factor (Crowe et al. 1994):
      • Blocks phagosome–lysosome fusion in phagocytic cells

      • Induces granuloma formation in mice (Han et al. 1998)

      • Analogous to Mycobacterium tuberculosis cord factor

    • Mycolic acids (Beaman and Moring 1988; Nishiuchia et al. 1999):
      • Found in the cell wall; associated with partial acid-fast staining

      • Increases hydrophobicity of cells and provides resistance to harsh environmental conditions

      • Analogous to Mycobacterium tuberculosis mycolic acids

  • Damage to host cells:
    • Phospholipases C (Vera-Cabrera et al. 2013):
      • Five potential PLC genes found in N. brasiliensis (not found in other Nocardia spp.)

      • Cytolytic activity; disrupts host cell membranes

      • Destroys host tissue; may play a role in cutaneous nocardiosis

    • Hemolysins (Barry and Beaman 2007):
      • Two genes identified

      • May be involved in the previously described ability of Nocardia spp. to induce caspase-dependent apoptosis in cultured human cell lines, possibly through activation of the host cell proteasome

  • Iron acquisition:
    • Siderophores:
      • Nocobactin (Hoshino et al. 2011):
        • nbt-like siderophore

        • Similar to M. tuberculosis mycobactin

      • Asterobactin (Nemoto et al. 2002)

References

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Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  • Douglas I. Johnson
    • 1
  1. 1.Department of Microbiology & Molecular GeneticsUniversity of VermontBurlingtonUSA

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