Mycobacteria and Medically Important Fungi

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Mycobacteria and Medically Important Fungi

• Louise S. Thai, M.D.

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? Mycobacterium tuberculosis
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Morphologic and Cultural Characteristics

• Slim, acid-fast rods
• Extremely slow growing
• Media Loewenstein-Jensen
• Cording on 7H-11
• Niacin production
• Resistant to disinfectants, except formaldehyde
  and glutaraldehyde
• Heat and UV sensitive

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Epidemiology

• 1/2 of the world population is infected and 30
  million people have active TB
• 8 million new cases per year and 3 million deaths
  due to TB yearly
• 1 infectious cause of death worldwide 6 of all
  deaths and 26 of avoidable adult deaths
• Susceptibility ?Native Americans Eskimos
• ?Caucasians ?Elderly immunocompromised
• Transmission via aerosols less contagious than
  most viral respiratory infections
• Morbidity Mortality in the U.S. steady ?
• 2002 15,075 cases

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TB Incidence in the U.S.
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Virulence Factors Cord factor
? Toxic to mice
? ?Granuloma formation
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Pathogenesis

• Rapid phagocytosis
• Prevention of phagolysosomal acidification
• pH in phagolysosome remains neutral despite the
  fusion of phagosome and lysosome
• Death of the alveolar macrophages

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Immune Response

• IL-2 and IFN-? produced by Th1 cells activate
  macrophages
• Activated macrophages kill ingested mycobacteria
• Killing by CD8 cells is mediated by IFN-?
• If ??? mycobacteria ????PMN, T-cells
  macrophages ? granuloma
• Macrophage lysosomal enzymes ? tissue damage
• TNF? ? caseous necrosis ? liquefied necrosis ?
  spread to other sites

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Clinical Aspects

• Asymptomatic infection when infected as adult
• Primary TB
• Develops after an initial exposure
• Usually in children lt4 years of age
• Is not infectious
• Secondary TB
• Is a result of reactivation of dormant infection
• Usually in adults
• Is infectious
• Miliary TB

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Diagnosis

• Skin test (PPD) 5 units of PPD are injected
  intradermally
• Positive RX induration of ?10 mm in diameter
  erythema
• Lab Diagnosis
• Direct smears stained by Ziehl-Neelsen
• Radiometric culture in 7H-11 medium with
  14C-palmitic acid ? 14CO2
• Gas chromatography of fatty acids.
• PCR

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Mycobacterium leprae

• Has not been cultured in laboratory
• Grown in mouse footpads and armadillos
• Tissue tropism skin and nerves

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Epidemiology

• Transmission
• Requires prolonged intimate contact
• ??? in nasal secretions
• ??? in the skin lesions
• Worldwide 12 million cases
• U.S. 96 cases in 2002
• lt 10 Native Americans
• The rest Immigrants

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Pathogenesis

• Intracellular Replication
• Two Clinical Forms
• Tuberculoid Low of AFBs, Lepromin
• Lepromatous High of AFBs, Lepromin -

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Clinical Aspects

• Incubation Period YEARS
• Tuberculoid
• Hypopigmented skin lesions
• Thickened nerves
• Anesthesia
• Lepromatous
• Multiple nodular lesions ? lion-like face
• Disfiguration

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Diagnosis and Treatment

• AFBs in skin scrapings
• Triple drug regimen
• Dapsone
• Clofazimine
• Rifampin

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Leprosy patient Before and After
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Medically Important Fungi
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General Characteristics

• Two Types Yeasts and Molds
• Yeasts single cells, reproduce by asexual
  budding or fission
• Molds produce long filaments (hyphae) and can
  reproduce sexually by mating and forming spores
• Most fungi of medical importance grow asexually
  by producing conidia (spores). Shape, color
  arrangement of conidia are the basis for ID.

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Pathogenesis

• No endotoxin in the cell wall
• Toxins
• LSD (lysergic acid diethylamide) produced by
  Claviceps purpura
• aflatoxin, a carcinogen produced by Aspergillus
  flavus
• Granuloma formation
• Fungal antigens ? cell-mediated immune system ?
  delayed type hypersensitivity RX

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Cryptococcus neoformans

• Causes systemic mycosis
• Lung infection
• Meningitis in AIDS patients
• Encapsulated yeasts
• Capsular staining with India ink

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Dimorphic Fungi
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Candida albicans

• Opportunistic
• Causes
• oral thrush
• diaper rash
• vaginosis
• nosocomial infections

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Diagnosis

• Budding yeasts and pseudohyphae in tissues
• Yeasts when cultured on blood agar, Sabouraud
  agar etc.
• Gram
• Germ tubes when incubated in serum- supplemented
  medium _at_ 37? C

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Candida albicans(Dimorphic)
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Coccidioides immitis(Dimorphic)

• Causes systemic mycosis
• Lung infection (fever, cough, chest pain)
• Disseminated coccidioidomycosis
• Spherules in tissue specimens
• Hyphae with arthrospores on Sabouraud agar _at_ 25?C
  
• Skin test

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Histoplasma capsulatum (Dimorphic)

• Causes systemic mycosis
• Pneumonia
• Disseminated histoplasmosis
• Oval budding yeasts inside the macrophages
• Hyphae with tuberculate macroconidia when
  cultured on Sabouraud agar
• Serology (e.g., immunodiffusion test)
• Skin test with histoplasmin

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Aspergillus fumigatus

• Opportunistic
• Causes
• Lung aspergillosis
• Systemic aspergillosis
• Septate branching hyphae
• Conidia (asexual spores)

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Dermatophytes

• Causes diseases of the skin and its appendages
• Direct microscopic examination of KOH preparation
  of the skin and nail scrapings
• Typical hyphae and conidia when cultured on
  Sabouraud agar at 25? C

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Antifungal Treatment

• Fluconazole
• Ketoconazole
• Severe cases of systemic mycoses
• Amphotericin B