mycobacterium and legionella

Question 1

mycobacterium

Answer 1

acid-fast bacilli; divide every 12-24 hours

Question 2

mycobacterium cell wall

Answer 2

acid fast; cell wall is lipid-rich (presence of mycolic acid), hydrophobic, resistant to many disinfectants; requires a lipid-soluble stain to visualize the bacteria; the bacteria resist staining by all other water-soluble stains

Question 3

mycobacterium tuberculosis epidemiology

Answer 3

humans are the only natural reservoir; spread person-to-person via infectoous aerosols; immunocompromised people have the greatest risk for disease; HIV infection greatly increases risk of TB

Question 4

m. tuberculosis virulence factors

Answer 4

can multiply and remain within alveolar macrophages is key to its virulence; the bacteria prevent lysosome-phagosome fusion while in the macrophage

Question 5

m. tuberculosis pathogenesis

Answer 5

TB is spread from person-to-person through the air by way of respiratory droplets; smaller droplets containing the bacteria may reach the alveoli where infection begins - the infectious dose is low

if the bacteris reach the alveoli, they are phagocytized by alveolar macrophages; prevent lysosomes from fusing to the phagosome; within the macrophage the bacteria multiply, forming the primary lesion or tubercle (granuloma)

Question 6

m. tuberculosis disease

Answer 6

primary infection is typically pulmonary; the infected macrophages form a mass surrounded by a dense wall of T cells, NK cells, and macrophages; this structure is called a granuloma; prevents further spread of the bacteria; if the granuloma is small, all bacteria will likely be killed; if the bacteria are not killed early during infection, the bacteria remain within the granuloma in a latent or dormant state; large granulomas become vascularized and are encapsulated in fibrin, protecting the bacteria from being killed; overtime the granulomas may begin to necrotize as their vascularization diminishes; secondary (active) TB develops when the necrotic granuloma meets an airway, forming a cavity which gives the bacteria access to the airway; active disease involves the upper lobe(s) of one or both lungs and includes pneumonitis or abscess formation and cavitation (holes in the lung tissue)

Question 7

Miliary tuberculosis

Answer 7

disseminated tuberculosis; occurs if the necrotic granuloma meets a blood vessel as opposed to an airway; the bacteria spread through the bloodstream; millet-like lesions; miliary TB may occur in other organs (including the brain); characterized by high levels of the bacteria in infected areas

Question 8

Why isn’t BCG vaccine used in the US?

Answer 8

TB is not endemic here so there is little need to protect newborns from the disease; most BCG-vaccinated individuals test positive for exposure to TB in the commonly used skin test- preventing surveillance from exposure to TB

Question 9

mycobacterium leprae

Answer 9

causes leprosy; these bacteria multiply very slowly; symptoms may develop up to 20 years after infection; disease symptoms are primarily from the host’s response to infection

Question 10

m. leprae epidemiology

Answer 10

spread person-to-person through either inhalation or skin contact with respiratory secretions or wound exudates

Question 11

m. leprae disease

Answer 11

chronic infection of the skin and peripheral nerves; the bacteria replicate inside phagocytic cells and never cells; the spectrum of tissue involvement is influenced by the patient’s immune status

Question 12

tuberculoid leprosy

Answer 12

strong cellular immune response; many lymphocytes and granulomas present in the tissue, but few bacteria; characterized by skin macules

Question 13

lepromatous leprosy

Answer 13

strong antibody response, but a weak cellular response; an abundance of bacteria is observed in dermal macrophages and Schwann cells; characterized by disfiguring skin lesions, nodules, plaques, thickened dermis, extensive nerve damage

Question 14

legionella pneumonophila

Answer 14

intracellular replication - replicate in free-living amoebae in nature and host cells during infeciton

Question 15

legionella pneumonopila epidemiology

Answer 15

commonly present in natural bodies of water and in air conditioning cooling towers and condensers and water systems (shower, hut tubs, etc.); human infection is most commonly associated with exposure to contaminated aerosols; person-to-person transmission has never been demonstrated; the bacteria parasitize amoebae in the water and replicate in this protected environment

Question 16

legionella pneumonophila pathogenesis

Answer 16

bacteria enter the respiratory tract through inhaled infectious aerosols; once in the lungs, the bacteria enter macrophages, monocytes, and alveolar epithelial cells of their host; the bacteria prevent the fusion of lysosomes to the phagosome once they are intracellular; infected macrophages release proinflammatory cytokines; the inflammatory response is characteristic of legionella infections

Question 17

legionella pneumonophila disease

Answer 17

pontiac fever: self-limited, febrile illness; influenza-like illness

legionnaire’s disease (legionellosis) - severe form of pneumonia; multi-organ disease is common