Mycobacterium Flashcards
Mycobacteria
Acid-fast (ZN-positive), rods, aerobic, catalase-positive, slow growing, intracellular pathogens, saprophytes (live in environment - water, vegetation), and transmitted from host to host. Cause granulomatous lesions in wide range of animals. Unique cell walls - lipid rich, containing mycolic acids.
Mycobacterium spp. of Clinical Importance
M. tuberculosis - tuberculosis in many animals. M. bovis - tuberculosis in cattle (also man, badgers) M. avium subspp. paratuberculosis - Johne’s dz in rumenants (diarrhea; Peyer’s Patches). M. leprae - leprosy in man, armadillos, mice.
C. perfringens
Enterotoxemia producing. Found in soil, feces, GI tract of animals and man. Canine HGE, Pulpy Kidney in sheep.
Mycobacterium Virulence Factors
MYCOLIC ACIDS: resists phagocytic digestion. SULFATIDES: prevents phagocyte activation and phag-lysosome fusion. LAM: prevents phagocyte activation and digestion. CELL WALL ANTIGENS: induce DTH (delayed-type hypersensitivity), a cell mediated immune response. SOD: superoxide dismutase (breaks down superoxide in phagocyte-lysosome).
Mycobacterium pathogenesis
The ability to mount an effective activated macrophage response determines the outcome. Less than 10% infected develop dz. 1. Infects, killed by imm response, no dz. 2. Infects, lies dormant, no dz (***MOST COMMMON***) 3. Infects, lies dormant, re-activates and causes acute dz. (Johne’s dz - lies dormant for up to 2 years before clinical signs are seen) 4 Infects, causes rapid acute dz. CANNOT spread to young via milk. Vaccines available.
Immune response to Mycobacterial Infection
CMI (cell mediated imm) required to limit the dz and provide protection. Ab response is irrelevant to protection. Mac’s (activated) contain the pathogens, accumulate, formation of a granulomatous response leads to development of tubercles.
Diagnosis of Mycobacterium
Ziehl-Neelsen staining method (bacilli stain red, other material stains blue). Very slow growing cultures - up to three weeks. Tuberculin test - two intradermal injections on neck (purified protein derivatives: one of avian spp. the other bovine), using calipers to test skin thickness before injections and 72 hrs after; if skin around bovine PPD is > 5mm thicker than that of avian PPD = positive test. However, infection with Mycobacterium must happen 30-50 days prior to test so that delayed-type hypersensitivity can develop. If tested before 30 = false negative.
Mycobacterium avium subspp. paratuberculosis
Johne’s dz. Diarrhea, emaciation, death. May take years to develop. Penetration of ileal mucosa and phagocytosis. Inflammatory response and eventual granuloma formation. Thickening of intestine and increased permeability which leads to loss of protein and poor dietary absorption….diarrhea. Ileum thickened and “corrugated” appearance grossly.
