Tuberculosis

Lecture 3

bacteria that causes tuberculosis

Mycobacterium tuberculosis

Mycobacterium tuberculosis

long and thin

acid-fast bacillus

strict aerobe (needs oxygen to survive)

slow growing

extremely thick, waxy cell wall

stains magenta/purple

generation time for tb

15-20 hours

how to stain tuberculosis

Ziehl-Neelson staining technique

mycolic acid and wax

gives tuberculosis a thick, waxy cell wall

makes it resistant to drying and disinfectants

also resistant to most antibiotics because of this cell wall

acid fast bacilli

rod-shaped bacteria that have a waxy cell wall rich in mycolic acids, making them resistant to decolorization by acid-alcohol during staining procedures.

Mycobacterium avium Complex (MAC)

tuberculosis infection that spreads to multiple parts of the body

seen in people with AIDS or immunocompromised individuals

transmission of tuberculosis

transmitted thru fine droplets of respiratory mucus suspended in the air

epidemiology of tuberculosis

considered a “disease of poverty” because its presence varies on certain living areas

malnutrition, weakened immune system, little medical care access, lung damage, and genetics raise risk of developing tb

explain what happens once the bacteria enters the lungs

1. bacteria is inhaled and enters the alveoli

2. bacteria is phagocytized by macrophages

3. bacteria prevents the fusion of the lysosome with the phagosome so it can’t be killed

4. cells send out cytokines to get help from nearby immune cells, meanwhile the tb is just multiplying inside the infected cell

5. immune and epithelial cells trap the infected cell so the bacteria can’t spread. this is called a tubercule

tubercule

protective nodule containing macrophages, lymphocytes, fibrous tissue, and a center of caseous necrosis formed by the immune system in response to M. tuberculosis. It represents a contained TB infection

what happens in an immunocompromised person who contracts tb

the bacteria can remain viable in the lungs and begin replicating again. This can either cause bronchopneumonia or the bacteria can spread through the blood and cause other diseases like hepatitis, renal parenchyma fibrosis, meningitis, potts disease, addison disease, or lymphadenitis

primary tuberculosis

bacteria are multiplying in the macrophages but get contained by tubercules. these become necrotic lesions that can become calcified. if the immune system is strong, the bacteria will die. in. an immunocompromised person, however, the bacteria will live and other symptoms occur

organs involved in extrapulmonary tuberculosis

lymph nodes

intestines

kidneys

long bones

genital tract

brain

meninges

secondary tuberculosis

dormant bacteria becomes reactivated even after several years

symptoms: violent coughing with bloody or green sputum, low fever, anorexia/weight loss, fatigue, night sweats, chest pain

60% mortality rate

testing for tuberculosis

mantoux test: protein is injected under the skin, if a raised bump forms that means you have been exposed to the bacteria b/c your T cells are responding to proteins

IGRA: blood test to see T cell reactivity to bacteria

acid fast stain of sputum

chest x-ray to look for tubercules

tuberculosis treatment

first 2 months: rifampin, isoniazid, ethambutol, pyrazinamide

4-7 months: two drugs that testing has shown to be effective

multidrug resistant tuberculosis

resistant to rifampin and isoniazid
requires longer, more intense treatments

extensively drug resistant tuberculosis

resistant to rifampin and isoniazid as well as fluoroquinolones and at least one second-line injectable drug

has very high treatment fail rates