Myobacterium I Flashcards by Joel Glotfelty

Thin, rod shaped (0.2 to 0.4 x 10 um)

-non-motile

Myobacterium

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What is the aerobic classification of myobacterium?

Obligate anaerobes

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Cell wall contains N-glucolylmuramic acid (instead of N-acetylmuramic acid) and has a very high lipid content

Myobacterium

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Has a slow growing doubling time. Anywhere from 30 h to 4-8 weeks

Myobacterium

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What are the four myobacterial-specific features of the myobacterial outer wall?

) Acyl lipids
) Mycolate
) Arabinogalactan
) Lipoarabinomannan (LAM)

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The lipid-rich myobacterial wall is highly impermeable. It shows up in

Acid fast stain

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Effective therapeutic target for anti-TBs

Lipid-rich wall

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What are the two faces of myobacterium on Gram stain sputum?

Ghosts (complete lack of staining) and Beaded GPR

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Binding of Carbol Fuchsin to mycolic acid is resistant to destrain by acid-alcohol; tissue and non-acid-fast organisms are counterstained with

Methylene blue

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Fluorochromes auramine O (green) and auramine-Rhodamine (orange) bind

Mycolic acid

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What is more sensitive fluorochrome stain or ZN stain?

Fluorochrome stain

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M. tuberculosis, M. bovis, M. bovis BCG, M. africanum, M. microti, and M. canettii make up the

Mtb complex

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All components of the complex cause TB so species level ID is not necessary for routine clinical purposes

Mtb complex

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What type of colonies does the Mtb complex form?

Non-pigmented colonies

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1/3 of the world’s population is infected

-8 million new cases and 2.9 million deaths annually in the world

Mtb disease

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TB is spread person to person through the air via

Droplet nuclei

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Mtb may be expelled when an infectious person:

Coughs, sneezes, speaks, or sings

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Occurs when another person inhales droplet nuclei and the bacilli reach the alveoli of the lungs

Mtb transmission

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Approximately 5% of Mtb infected patients develop transmissable

Pulmonary disease

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Chronic clinical course with delays in diagnosis and treatment contribute to

Mtb transmission

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M. bovis BCG is less transmissible than

M. tuberculosis

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Droplet nuclei containing tubercle bacilli are inhaled, enter the lungs, and travel to

Alveoli

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Then, tubercle bacilli multiply in

Alveolar macrophages

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Within 2 to 8 weeks, cell mediated immunity develops and activated macrophages surround the tubercle bacilli; these cells form a

-Keeps the bacilli contained and under control

Barrier Shell (granuloma)

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The presence of slender acid-fast positive, slightly curved and beaded bacilli, is suggestive of

Myobacteria

In most individuals, TB infection remains latent due to

Immunity (delayed type hypersensitivity)

Can be demonstrated by positive interferon-γ release assay or tuberculin skin test

DTH

The tuberculin skin test (TST) is also known as the

Mantoux test

The antigenic reagent of the Mantoux test is tuberculin (Mtb extract) or a

Purified Protein Derivative (PPD) of Mtb

In the PPD test, at 48-72 hours, we measure the ring of

Induration (not redness)

A PPD test > 15mm: considered positive for

Any persons

A PPD test > 5 mm: considered positive for

High risk populations

Like TSTs, these measure a person's immune reactivity to Mtb

Interferon-γ release assays (IGRAs)

Blood T-lymphocytes from most persons that have been infected with Mtb will release

Interferon-γ (IFN-γ)

Whole blood alone: provides baseline level of

IFN-γ

Whole blood plus Mtb peptides: measures stimulated IFN-γ release in response to

Recombinant specific Mtb antigens

Whole blood plus a non-specific activator of WBCs (mitogen): demonstrates that WBCs are present and capable of secreting

IFN-γ

Performing a second diagnostic test when the initial test is negative is a strategy to increase

Sensitivity

Performing a second diagnostic test when the initial test is negative is a strategy to increase sensitivity, but this may reduce

Specificity

Performing a confirmatory test following an initial positive result is based upon both the evidence that

False positives are common

If the immune system CANNOT keep tubercle bacilli under control, or later becomes compromised (HIV, iatrogenic, age), focal granulomata break down and organisms

Escape, replicate, and can disseminate

Active disease may represent reactivation, reinfection or progressive

Primary infection

What are the intermediate risk factors for disease progression to TB?

Diabetes, Chronic renal failure, and Intravenous drug use

What are some of the high risk factors for disease progression to TB?

HIV infection, immunosuppressive therapy, Silicosis, and abnormal CXR

A person has no symptoms if they have a

Latent TB Infection (LTBI)

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

Miliary TB

Diffuse miliary pattern is associated with appearance of

Millet Seeds

Tissue injury is a consequence of immune response instead of specific

Toxins virulence factors

Sputum*, aspirate, bronchoalveolar lavage (BAL), gastric lavage (GL) are respiratory specimens for

TB testing

TB can also be tested for in the -Does not require 24 hour test

Urine

High volume of urine and tissue and body fluids to test for

In an immunocompromised patient, we can test for TB by testing the

Blood

Specimens collected from normally sterile sites can be directly stained and inoculated to media, typically following a

Concentration step

Specimens from non-sterile sites must first be decontaminated before further

Analysis

Responsible for Liquefaction of non-sterile specimens

N-acetyl-L-cysteine (NALC)

Kills contaminating bacteria

NaOH

What are the two ways for direct pathogen visualization of TB?

Acid-fast stain and Fluorochrome stain

The detection limit of the acid-fast stain is 10^4 AFB. What is the sensitivity of this test?

20-80%

More sensitive than Acid-fast stain -All positives must be confirmed using acid-fast stain or by another observer

Fluorochrome stain

Some AFB do not stain well with

Fluorochromes

Contamination should be an important consideration with

Direct pathogen visualization

A characteristic of Mtb in the acid-fast stain is

Cording

A virulence factor (toxic to phagocytes and other cells)

Cord factor (trehalose dimycolate)

It fluorescences only in lipid environment (e.g., after metabolic incorporation into the outer membrane of mycobacteria) and not in aqueous solutions -Artificial precursor of mycolic acids

Solvatochromic Trehalose

Very fast and does not require any washes

Solvatochromic Trehalose

Staining with Solvatochromic Trehalose requires

Bacterial metabolic activity

What kind of staining will we see with 1. ) Life Mtb 2. ) Dead Mtb 3. ) Effective antibiotic-treated Mtb

1. ) Strong staining 2. ) No signal 3. ) Weak staining

2017 ATS/IDSA/CDC guidelines recommend that both solid media and liquid media be inoculated for all specimens and incubated for

8 weeks

Liquid media reduces

Average turn around time (TAT)

Nucleid acid probes can be used for

Identification of TB

All US clinicians and public health TB programs should have access to molecular tests to aid in the diagnosis of TB. Standard practice should include

NAA testing

Should be performed on at least one respiratory specimen from each patient with signs and symptoms of pulmonary TB

NAAT testing

For NAATs, is similar to that for smear examination but weeks faster than culture

Turn-Around-Time (TAT)

NAATs are superior to smear examinations because they have greater

Specificity (`95% PPV) and Sensitivity

~50-80% of smear negative, culture positive specimens are

NAAT positive

It is recommend that acid-fast bacilli (AFB) smear microscopy be performed in all patients suspected of having

Pulmonary TB

Should both be performed for every specimen obtained from an individual with suspected TB disease

Liquid and solid myobacterial cultures

CDC suggests performing a diagnostic nucleic acid amplification test (NAAT) on the initial respiratory specimen from patients suspected of having

Pulmonary TB

In AFB smear-negative patients with an intermediate to high level of suspicion for disease, what can we use as presumptive evidence of TB disease?

Positive NAAT

Appropriate NAAT include the

MTD test and MTB/Rif test

Ubiquitous environmental organisms that may colonize or infect humans

Non-tuberculous Myobacteria (NTMs)

Pathogenesis may include trauma, inhalation of infectious aerosols or ingestion

NTMs

What are the four clinically important NTMs and Runyon classification?

Group 1: Photochromogens Group 2: Scotochromogens Group 3: Nonphotochromogens Group 4: Rapid growers

M. kansasii and M. marinum (low temp) are two examples of

Photochromogens

M. gordonae, M. xenopi, and M. scrofulaceum are two examples of

Scotochromogens

M. avium complex (MAC) and M. ulcerans (low temp) are two examples of

Nonphotochromogens

M. abscessus, M. chelonae, and M. fortuitum are the three

Rapid growers

Causes chronic pulmonary infection involving upper lobes of the lungs, resembles Mtb clinically

M. Kansasii

A major reservoir for M. Kansasii is

Tap water

Dissemination is rare except in AIDS -Responds quickly to antimicrobial therapy

M. Kansasii

Sometimes cording is observed with M. kansasii but it is ID'd by

DNA probe

M. Kansasii is classified as a

Photochromogen

Cutaneous infection associated with exposure to salt/freshwater following trauma

M. marinum

M. marinum causes which two granulomas?

Swimming pool granuloma and fish tank granuloma

Most common in southern coastal states - Grows slowly at 30 ⁰C (no growth at 37 ⁰C) - Photochromogenic

M. marinum

How do we ID M. marinum?

Biochemical/molecular ID

Most commonly recovered nonpathogenic NTM (no treatment needed)

M. gordonae

Found in soil and water, and it colonizes the respiratrory tract -Long, wide, branching, beaded AFB

M. gordonae

M. gordonae is classified as a -i.e. it has pigmentation in the dark or in the light

Scotochromogen

We use a DNA probe for ID of

M. gordonae