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35 Cards in this Set
- Front
- Back
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What are the characteristics of Mycobacteria?
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1. weakly gram +
2. stain better with acid fast stain 3. obligate aerobe |
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What bacteria cuases TB? what are the problems assoc with TB?
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M. tuberculosis.
TB is a major human disease effecting healthy people which poses a problem for those with AIDS and TB has multiple drug resistance |
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who are M. avium- M. intracellulare complex (M. avium)?
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atypical mycobacteria which generally effects birds and other animals. NOw 50% of AIDS ptnts have MAI (mycobacterium avium-tracellulare)
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who does MAI infect?
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It is a major bacterial opportunist for AIDS patients and carries multiple drug resistance.
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Where does M. bovis come from and where do you find it?
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spread from cattle, and is rarely seen in developed countries.
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What does M. leprae cause and where is it found?
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leprosy, it's is a majory disease of 3rd world and rarely found in developed coutnries.
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What are the general features of M. tuberculosis?
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1. They are obligate aerobes adn therefore grow in lung apex
2. have an extraordinary cell wall which is rich in lipids (reason for acid fast staining). 3. They have slow growth (making culture not the first choice for Dx)--> 3-8wks for pos culture |
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Describe the primary stage of infection
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inhale air droplet which goes to upper airways adn lower lobes of lungs--> proliferate and recongized by macrophages via CR3 &CR4 rec--> bacteria evade harsh conditions inside alveolar macrophage--> most macrophages beocme infectious centers themselves, addeing to the problem while some presnt antigen to Th cells which may illicite IR--> in other cases bacteria penetrate regional lymph node (Gohn focus)and spread to highly oxygenated area [lung, vertebrea, kidney, long bones]
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how is TB transmitted?
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aerosol: coughing, sneeszing, talking and is increased in a closed environemtn.
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What is course of TB if the MQ presents the ag?
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primary infection takes 2-8 wks. supposing MQ is activated it activates T cells which secrete cytokines--> T cell recruitment leads to seclusion of bacteria--> forms a granuloma: circular structure w. immune cells surrounding TB bacteria, called tubercule.
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How do macrophages continue the spread of the primary TB infection?
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They release an enzyme which causes necrosis and can disrupt th bronchus and give the bacteria a tunnel with which to travel to outside of wall where there is air adn can go on to infect others(infection is spread and cavity is formed)
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What follows healing of the primary infection?
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calcification
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What are the 2 options after bacteria is inhaled, mult in MQ and form a lesion?
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1. it will activate macrophage to stop growth and trigger IR
2. reach stationary phase and survive inside granulomas |
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When do you get reactivation?
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bacteria proliferate in MQ and form more lesions which liquefy adn spread bacteria to blood adn organ and may lead to death
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What causes reactivation?
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immunosupression as in AIDS
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How do you Dx TB?
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1. white spot on xray: granuloma, ghon focus, scarring in upper lobes, tb pneumonia
2. PPD skin test (protien purified derivative): indicates past exposure, shows delayed hypersensitivity 3. sputum acid fast stain and culture (slow) 4. PCR- can get false pos |
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What happens 90% adn 10% of the time in primary infection
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90%- asymptomatic, bacteria killed completely
10%- penumonia |
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where do you get reactivation of TB (post primary TB) and what are the chances at various times?
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Reactivation occurs from dormant bacteria at the prmary infection.
5% chance in 1st 2 years 5% throughout life = 10% |
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What causes reactivation?
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immunodeficiency: HIV, chemo, age
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What are the symptoms of the reactivation of TB?
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rever, night sweats, wt loss, cough, hemoptysis, fatigue
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What is a Ghon focus?
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calcified tubercle in middle or lower lung zone
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What is Miliary TB?
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a form of tuberculosis that is characterized by a wide dissemination into the human body and by the tiny size of the lesions (1-5 mm). Its name comes from a distinctive pattern seen on a chest X-ray of many tiny spots distributed throughout the lung fields. Miliary TB may infect any number of organs including the lungs, liver, and spleen. It is a complication of 1-3% of all TB cases.[1]
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Mycolic Acids
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part of mycobacterial cell wall: exremely long chian unique to mycobacteria, nocardia, and cornebacteria
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Cord factor
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mycoside found only in TB, responsible for aggregation of bacteria
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Wax D
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mycoside, part of cell wall that acts as adjuvant (enhances antibody formation to an ag)
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Acid fast stain
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1. Acid fast: when you add die to certain bacteria and wash with acid and it holds the die--> about the same amount that hold the dye form colonies (100%)
2. should not be used instead of culture b/c other bacteria can be seen with staining 3. AFBacteria smears req 10^5 AFB/ml of sputum for recongition by direct microscopy while cutlure req only 10-100 CFU (colony forming units)/ml in sputum 4. AFS is goo for active disease adn when bacterium has access to spatulum, wall. |
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How are stained smears fo sputum helpful?
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1. provides Dx of mycobacterial disease
2. allows most infectious cases (smear +) to be quickly identified 3. may be used to follow success of chemo of TB patients by following titer in sputum 4. impt in assesing risk of comtamination 5. confirm cultures. |
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PCR for Dx of TB
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1. PCR targets 16s rRNA, which differs from species to species so you can make a primer that only recognizes mycobacteria
Advantages: sensitive, specific to type of bacteria, rapid, simple Limitations: No susceptibility, false pos/neg, expensive, infection/disease? |
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What are the characterisitcs of M. tuberculosis culture?
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slow growing, no pigment, culture on medium with ab to prevent growth of non mycobacteria
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What is PPD test?
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purified protein derivate skin test: expose skin adn intorduce ag and w/in 48-72 hrs see redness of IR
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How do u measure resutls of PPD?
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>10mm: exposure to bacteria in past
>15mm: diamerter is larger if you were exposed >5mm: in immunocompromised patietns who were exposed recently but IS yeilds weak response |
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BCG
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bacillus Calmette- Guerin vaccine for TB- given in other countries, debatabley effective, yeilds false positive
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M. tuberculosis VS
M. bovis |
TB: source is droplets, disease is TB of lung, prevention is isolation adn the reservoir are other humans.
Bovis: source is milk, the disease is TB of intestine, it is prevented by pasteruization, and the reservoir is bovine |
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Summarize TB pathogenesis
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Infect lung--> distribute w/in macrophages--> it's facultative intracellular pathogen; inhibits pahgosome-lysosome funsion adn resists lysosomal enzymes.
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Tx for TB?
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bed rest, food, resh air, sun i.e. improve physiological situation
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