(From Micro, 19 Oct 2000, by Brian Buschman)
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TB is acid-fast (with Norcardia) and infects 1/3 of AIDS patients. They are obligate aerobes and are bacilli.
They have lipids and glycosides called mycolic acid, mycoside and sulfatide.
When infected the immediate response is for macrophages to engulf them and carry them all over the body. They are resistant to macrophage degradation. The secondary response to TB is for them to proliferate all over the body but for a cell-mediated response to kill them. Also at this time the macrophage attack does a number on the local tissues causing caseous necrosis.
PPD tests look for cell-mediated response showing previous or current exposure. A gales negative can be seen in patients without a normal immune response. AIDS, malnutrition, steroids and so on. If you are unsure about the negative then do a Candida PPD test to see if there is response. Since Candida is normal flora you know that it should be positive.
TB gets in and is carried by macrophages as discussed. It can be symptomatic or asymptomatic at this point.
A) Most are asymptomatic as the mycobacterium are so small they seal themselves inside a granulomas which is healed over with fibrosis or calcification.
These are called Ghon focuses in the lungs or Ghon complexes in association with infected LNs.
B) Symptomatic TB is seen with peds, old people and immunocompromised. It created holes in the lungs with a fluid/water interface that is visible on x-ray.
Reactivation of any place seeded has a 10% lifetime chance or if HIV infected 10%/year.
1) Reactivation can occur in the lungs in the lower upper lobe due to higher O2 tension. In the primary infection it is in the upper lower/middle lobes. It shows night sweats, fever and productive bloody cough.
2) Pericardial and pleural TB causes fluid in the spaces. This leads to decreased FEC and/or cardiac tamponade.
3) Scrofalia is the term for LN TB infection.
4) Kidney infections show blood cells but no bacteria on life stain. It takes weeks to get a positive culture.
5) It causes destruction of IV discs.
6) Arthritis, usually only of one joint.
7) Meninges and brain
8) Miliary TB has millet-seed size granulomas all over the body. It can be seen on a chest film.
Diagnose TB with:
1) PPD
2) Chest X-ray for granulomas, Ghon foci, Ghon complexes or old scaring in U.L.
3) Acid-fast sputum.
In the US leprosy is mostly seen among immigrants. The bacteria grow best in cool places like the face, testis and all. There are 5 types but only two are important. The other three are just combinations and mild cases of the two.
1) Lepromatous leprosy which is the worst because patients can’t fight it. They have no delayed-hypersensitivity response (or PPD response). They have deformed skin and leonine faces.
Peripheral nerve damage causes loss of sensation. Loss of sensation leads to trauma and 2o infection.
2) Tuberculoid leprosy (TL) patients have isolated skin legions that sometimes effect the most superficial nerves. It is often self limiting.
M. kansaii has TB like granulomas superficially. They can be gotten from scratches in swimming pools.
M. scrofulaceum causes lymphadenitis in children.
M. avium is seen in immunocompromised patients infected with this bacteria that is everywhere. It is highly resistant to Mycobacterial drugs.
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