Nocardia, Actinomyces, Rickettsia

• Nocardia


  Gram (+), partially acid-fast rods, which grow slowly in branching chains resembling fungal hyphae

  
• 3 species that cause nearly all human Nocardia infections

  • N. asteroides
  • N. brasiliensis
  • N. caviae

  
• Nocardia species


  • Distinguished by proteolytic and fermentation patterns in culture

  
• Nocardiosis


  The most common manifestation is pneumonia: fever, weight loss, cough, pleuritic chest pain, and dyspnea

  
• Nocardiosis

  • In about 20% of patients there are granulomatous skin lesions and/or CNS abnormalities

  
• Nocardiosis infection

  1. Inhalation of airborne bacilli from an environmental source (soil or organic material)

  2. Disease is not contagious

  
• Skin lesions caused by N. brasiliensis

  Often result from direct inoculation
• Nocardiosis


  • Subverts antimicrobial mechanisms of phagocytes, causing abscess or rarely granuloma formation with hematogenous or lymphatic dissemination to the skin or central nervous system

  
• Mortality is up to 45% even with therapy
• Nocardiosis


  Rare in normal persons, usually occurs in recipients of organ transplants; in patients with leukemia, lymphoma, humoral, or leukocyte defects; or after prolonged steroid therapy

  
• Diagnosis of Nocardiosis

  Gram stain, modified acid-fast stain, and culturing of organisms from sputum, bronchoscopic specimens (washing, brushing), aspirates of abscesses, or by biopsy

  
• Treatment of Nocardiosis


  Prolonged (up to 1 year) therapy with trimethoprim-sulfamethoxazole
• Actinomyces


  Gram (+) rods grow as filaments, branching rods, and diphtheroidal rods
• Actinomyces species associated with humans and animals

  • 19 species
• Typical actinomycosis in humans

  Chronic disease caused by Actinomyces israelii, A gerencseriae and Propionibacterium propionicus (previously Arachnia propionica)
• Actinomycosis infection

  • Characterized by persisting swelling, suppuration, and formation of abscesses with draining sinuses
• Major types of actinomycosis

  • Cervicofacial
  • Thoracic
  • Abdominal
• Actinomyces species

  • Some have also been isolated from other mixed anaerobic infections, eye infections, blood and the urinary tract
• Actinomycosis

  1. Endogenous oral bacteria are introduced into tissue

  2. Abscesses with fibrous walls and pus with sulfur granules develop

  3. Lesions spread by direct extension
• Actinomycosis is endemic; sporadic cases occur worldwide
• Actinomycosis is generally unrelated to age, sex, season, or occupation
• Some Actinomyces spp.

  Associated with other mixed anaerobic infections and in infections in severely compromised patients, can be significant opportunist pathogens
• Actinomycosis


  Suggested by a suppurative lesion with Gram (+) filaments in the exudate, sulfur granules may be present
• Diagnosis of actinomycosis and other infections involving Actinomyces

  Confirmed by isolation and identification of the bacteria
• Good oral hygiene may help in prevention of actinomycosis
• Treatment of actinomycosis

  Antibiotics and surgical drainage of lesions, penicillin is the drug of choice
• Rickettsiae

  Diverse collection of obligately intracellular Gram (-) bacteria found in ticks, lice, fleas, mites, chiggers, and mammals
• Genera of rickettsial pathogens

  • Rickettsiae
  • Ehrlichia
  • Orientia
  • Coxiella
• Rickettsial pathogens


  • Zoonotic, cause infections that disseminate in the blood to many organs
• Rickettsial antigenically defined groups

  • Spotted fever group
  • Typhus group
• Scrub typhus rickettsiae


  Differ in lacking lipopolysaccharide, peptidoglycan, and a slime layer, and belong in the separate, although related, genus Orientia
• Transmission of Rickettsia and Orientia species

  1. By the bite of infected ticks or mites or by the feces of infected lice or fleas

  2. From the portal of entry in the skin, rickettsiae spread via the bloodstream to infect the endothelium and sometimes the vascular smooth muscle cells
• Rickettsia species

  Enter their target cells, multiply by binary fission in the cytosol, and damage heavily parasitized cells directly
• Diseases caused by Rickettsia species


  • Rocky Mountain spotted fever
  • Rickettsialpox
  • Other spotted fevers
  • Epidemic typhus
  • Murine typhus
• Orientia (formerly Rickettsia) tsutsugamushi


  Causes scrub typhus
• Rickettsioses


  • Patients present with febrile exanthems and visceral involvement; symptoms may include nausea, vomiting, abdominal pain, encephalitis, hypotension, acute renal failure, and respiratory distress
• Diagnosis of rickettsioses

  Difficult both clinically and in the laboratory, cultivation requires viable eukaryotic host cells, such as antibiotic-free cell cultures, embryonated eggs, and susceptible animals
• Treatment of rickettsioses

  Rickettsia species are susceptible to the broad-spectrum antibiotics, doxycycline, tetracycline, and chloramphenicol
• Prevention of rickettsioses

  Exposure to infected arthropods offers some protection, a vaccine exists for epidemic typhus but is not readily available