- Why the lung is preferentially affected.
- Why the secondary infections start at the apex of the lung.
Acid-Fastness (For Mycobacteria, Gram Positiveness is Only Academic)
- Acid fast bacteria have the ability to retain dyes (fuchsin) when treated with
acid solution (Ziehl-Neelsen stain).
- Useful for the detection of M. tuberculosis in clinical specimens (sputa, pus or
tissues) by microscopy.
Special Nutritional Requirement (Lowenstein-Jensen Medium)
- TB cultures are not routinely done! Need special culture media.
- Requires several weeks to form visible colonies! (DON'T CALL CLINICAL LABS FOR
THE RESULT OF CULTURE NEXT DAY!)
Highly Resistent to Desiccation
- This is why most infections (TB) are initially caused by inhalation of
Facultative Intracellular Pathogen
- Neutrophils or resident macrophages can not kill this organism. M. tuberculosis
prevents the acidification of phagolysomes, thus resists the intracellular microbicidal
mechanisms of phagocytes.
Unique Cellular Constituents (Lipids)
- Stimulate cell-mediated immune response (delayed type hypersensitivity) of the
host (see the pathogenic mechanisms and tuberculin test below).
- þ The constituents listed below are found largely in cell walls. Mycobacterial
cell walls can induce delayed hypersensitivity, and replace whole mycobacterial cells in