Fan - Mycobacteria Flashcards
Kochs postulates
1) the microorganism must be found in abundance in the animal suffering from the disease
2) the microorganism must be isolated from a diseased organism and grown in pure culture
3) the cultured microorganism should cause disease when introduced into a healthy organism
4) the microorganism must be reisolated from the diseased experimental host.
General characteristics of Mycobacterium
Rod shaped Obligate aerobe Non motile Cell wall contains N-glucolylmuramic acid (instead of the usual N-acetylmuramic acid) Acid Fast Slow growing Over 100 species
WHat does it mean to be acid fast?
Being acid fast basically means that the bacteria is resistant to being destained by acids/ethanol during staining procedures. So when we use acid/ethanol do destain during gram staining, it wouldn’t work properly for this genre of bacteria
What types of stains do we use on mycobacterium because they are acid fast?
Ziehl-Neelsen (acid-fast stain)
Fluorochrome stain
Symptoms of TB
Fever, night sweats, anorexia, weight loss, long term cough with pulmonary infection, could cough up blood, pain in chest.
TB transmission route
Droplet nuclei in the air. Eventually the bacilli get to the alveoli of the lungs.
- sneezes, coughs, etc.
Factors affecting probability of transmission?
Susceptibility of exposed person Infectiousness of TB patient Environment in which exposure occurred Exposure length, proximity, and duration Virulence of tubercle bacilli - each strain is different but can cause TB anyway.
Where do tubercle bacilli multiply?
In alveolar macrophages
What occurs once the infection is in the lung?
Within 2-8 weeks, cell mediated immunity develops and activated macrophages surround the tubercle bacilli and create a granuloma that keeps the bacilli contained and under control.
What type of hypersensitivity does TB exhibit?
Type IV Hypersensitivity, which means that it can take 48-72 hours to see the immune system reacting.
What are the two ways to test for TB?
Tuberculin Skin Testing (TST)
Interferon Gamma Release Assays (IGRAs)
Tuberculin Skin Testing (TST)
Inject antigen intradermally. 48-72 hours look for ring of induration (not redness) and measure it. Depending on the level of risk we have different cut offs.
>5 mm cutoff is for people in high risk population - HIV, organ transplant, recent contact with TB person
>10 mm cutoff is for people in moderate risk population - immigrants from countries with a lot of TB
>15 mm cutoff is positive for all people
- this test it preferred in children elbow the age of 5
Interferon Gamma Release Assays
Also test a person’s immune response to Mtb. The benefit of this one is that it works on people who have had a BCG vaccine and the patient doesn’t have to come back a second time to have it read.
What does it mean when you say that the disease is active?
For whatever reason the immune system can’t keep the tubercle bacilli in check and the granuloma breaks down and the organisms escape and disseminate to other parts of the body.
- essentially the patient is become reinfected.
Risk factors for Mtb progression
People w HIV
Infants below age 5
People receiving immunosuppressive therapy
People who were recently infected
People with untreated TB or inadequately treated TB
People with diabetes renal failure, leukemia, lymphoma, or silicosis
People who are malnourished
Cigarette smokers, drug and alcohol abusers
Military TB
Occurs when a TB infected lymph node erodes a vessel wall and tubercle bacilli are spread through the blood stream to other parts of the body and the rest of the lung.
- on an X-ray you will often see what are called millet seeds.
On gross pathology what would you see in the tissues of someone with TB?
Caseous necrosis
Lab diagnosis of mycobacterial infections
1) first you collect specimens from the patient
- RUST Blood Wounds
- Respiratory, urine, stool, tissues, blood, wounds.
2) If the specimen is from a sterile site you can put it straight on media, otherwise you have to decontaminate the subject.
3) You can then attempt to do direct pathogen visualization if you have a large enough sample on either an acid-fast stain or a fluorochrome stain
4) If you didn’t have a large enough sample, say you got a gastric lavage, then you have to cultivate the specimen for about 8 weeks.
5) You can then identify via acid fast stains or Nucleic acid probes.
What is cording?
Something that Mtb does when visualized under a microscope. It looks kind of like a snake. It is due to something within their cell wall.
NAAT
Nucleic acid amplification test
- Used instead of smear/culture but is better due to better spe and sen and quick turnaround time.
What are the two subgroups of mycobacteria
Mycobacteria TB - Mtb
NonTB Mycobacteria - NTMs
NTM classes
Photochromogens - M. Kansasaii, M. Marinum
Scotochromogens - M. Gordonae, M. Xenopi, M. Scrofulaceum
Nonphotochromogens - M. Avium complex (MAC), M. Ulcerans
Rapid growers - M. Abscessus, M. chelonae, M. Fortuitum
M. kansasaii
- Causes chronic pulmonary infection involving upper lobes of the lungs, resembled Mtb clinically.
- tap water is major reservoir
- photochromogen
HINT - KANSAS, they probably have bad tap water of there and I feel like living there will give you lung disease
M. marinum
- cutaneous infection associated with salt/freshwater following trauma
- causes “swimming pool granuloma” or “fish tank granuloma”
- photochromogenic
HINT - MARINA
M. gordonae
- most common NTMs
- found in soil and water
- can colonize respiratory tract
- Scotochromogen
M. xenopi
- grows in hot water
- causes chronic pulmonary disease in adults with underlying lung disease
- Scotochromogen
Mycobacterium avium Complex (MAC)
- most commonly isolated Mycobacterium species
- environmental reservoir
- non-chromogenic
Rapid growing mycobacteria
M. Abscessus is one example.
- growth in less than 7 days
- usually post-traumatic, post-surgical, post-injection would infections.
- causes chronic pulmonary infections
- likes lower temps
- arylsulfatase positive
- antibiotic susceptibility tests are important
M. Leprae
- spread person to person via nasal secretions
- causes anesthetic skin lesions
Photochromogen
Forming pigment on an agar only after exposure to light.
Scotochromogenic
Pigmentation on in the dark or light.
