Mycobacteria and Spirochetes Flashcards
Prevention of Lyme disease
Warn people to minimize exposure to ticks: Wear long pants, use tick spray, and check for ticks afterwards. Removal within the first two days is likely to prevent infection.
A Lyme vaccine based on OspA was previously available in the US, but has been withdrawn from the market.
Cellular immunity is not very strong until age _____ in kids
Cellular immunity is not very strong until age ~5 or 6 in kids
What type of immune response is tested in a tuberculin skin test?
Cell-mediated immunity
specifically Helper T cell immunity
Testing for Lyme: What is actually done?
First, a B. burgdorferi antigen ELISA (Sensitive, non-specific, low cost)
If this gives a positive, proceed to:
B. burgdorferi antigen Western blot (Sensitive, Specific, Expensive)
Mycobacteria have the unusual staining property of _____
Mycobacteria have the unusual staining property of retaining basic dyes when treated with acidic solutions.
This is due to the mycobacterial envelope, which contains waxes composed of long-chain branched hydrocarbons.
Mycobacterium tuberculosis epidemiology
- Infects 1/3 of world population
- Especially easily transmitted among populations in crowded living conditions with little native resistance
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Has greatest impact in resource-limited countries where HIV rate is high
*
Primary vs Secondary tuberculosis
Primary: Occurs shortly after infection
Secondary: Occurs later, after a latency period.
Treatment of Lyme disease
Doxycycline for adults, amoxicillin for kids.2-4 week courseforstage I, stage II,andstage III manifesting as arthritis.
Stage III manifesting as neurological symptoms requires intravenous 3rd generation cephalosporine (ceftriaxone).
Immune reconstitution inflammatory syndrome
When an immunocompromised patient has TB and you activate the immune system, the symptoms are exacerbated because immune cells are the major cause of symptoms in TB infection.
Borrelia burgdorferi-mediated disease
Cause Lyme disease. Begins as local infection and spreads to form erythemia migrans (bull’s eye). This is indicative ot stage I Lyme disease.
Within days to weeks, infection may spread via the blood to distant sites. The first metastasis is indicative of stage II Lyme disease. Cardiac involvement may lead to atrioventricular block or myopericarditis.
After months to years of latent infection, spirochetes may appear in the joints, nervous system, or skin. This is indicative of stage III Lyme disease. Repeated episodes of pauciarticular arthritis are a common presentation.
What type of immune cell beside macrophages is most important to the response to M. tuberculosis?
Helper T cells!!!! Which provide help to the macrophages and activate them to kill intracellular tuberculosis.
Primary tuberculosis pathology
Airborn droplet nuclei reach the alveoli. They are engulfed by alveolar macrophages, but mutiply inside and lyse these macrophages (M. tuberculosis is facultative intracellular).
Acute inflammation occurs, bringing in more leukocytes. Some leukocytes bring TB back to regional lymph nodes. May result in Ghon complex, where hilar lymph nodes are enlarged. In nonimmune host, TB then spreads hematogenously. This may result in seeding of the lung apeces. Here progressive primary or secondary disease can occur.
Borrelia burgdorferi-mediated damage
The spirochete persists in infected tissues and elicits an immune response that causes injury to the host.
- Does not produce LPS, but produces a variety of other lipoproteins which stimulate TLRs.
- Spirochetes coat themselves in plasmin to be able to move unrestricted through tissues. This creates the rash expansion.
- Adherence to host ECM is critical to ability to colonize and to virulence.
- Once infection is established, B. burgdorferi may survive for years.
- Binds complement-regulating factors to prevent complement activation.
- Exhibits antigen rotation.
- Reduces expression of OspC for ~one week after entering host to avoid the antibody response.
Important airborne pathogens:
Mycobacterium tuberculosis, measles, and varicella-zoster (chicken pox)
Diagnosis of Borrelia burgdorferi infection
- Culture from infected sites is the gold standard
- The diagnosis of stage 1 Lyme disease depends on erythemia migrans observation with history of tick bite (Often this occurs prior to any detectable antibody titer)
- Serological ELISA is used to diagnose stage 2 and 3 Lyme Disease
Best way to stain Mycobacteria
- Heat with basic red dye fuscin
- Treat with HCl in ethanol to remove from other cells (except mycobacteria and other acid fast bacteria)
- Counterstain with a blue dye
TB Granuloma (necrotizing granulomatous inflammation)
Interpretation of immunological TB assays
- A newly positive test after a previous negative test indicates recent tuberculous infection and is an indication for chemoprophylaxis
- They are most useful for diagnosing latent tuberculous infection
- The tuberculin skin test is much less useful in countries where most of the population is tuberculin positive or has received the bacille Calmette-Guérin (BCG) vaccine
- About 15% of individuals with active TB have negative tests.
- Not useful for immunocompromised persons
Prevention of Mycobacterium tuberculosis infection
Improving the standard of living decreases rates of disease. Currently there is no effective vaccine, mostly because antibodies do not provide protection against tuberculosis.
bacille Calmette-Guérin (BCG) vaccine is an attenuated strain of Mycobacterium bovis.
Not used in the US because it does not provide much protection and decreases the effectiveness of TB screening.
Major assays used to look for TB?
Interferon gamma release assay
PPD test
Gold standard for TB diagnosis
Culture
But, it takes a long time, and you may need an indication sooner.
Borrelia are classified as. . .
obligate intracellular gram-negative spirochetes
They grow very slowly and are difficult to detect in culture
____ is typically the latest manifestation of Lyme disease
arthritis is typically the latest manifestation of Lyme disease
Mycobacteria grow much more ______ than most other bacterial pathogens
Mycobacteria grow much more slowly than most other bacterial pathogens
Stage II Lyme presentations
Meningitis
Carditis
Cranioneuropathy (facial nerve palsy, “drooping face”)
Multiple erythema migrans
Lyme disease diagram
Borrelia burgdorferi toxins
None! Lyme disease does not involve any toxins.
VlsE
Protein in spirochetes that exhibits antigen rotation. This means that antigenic sites on the protein may be varried while maintaining function, and is an excellent way to evade the immune system.
Diagnostic tests for tuberculosis
Tuberculin skin testing: tests for reactivity to TB proteins in skin.
Interferon Gamma Release Assays: Measure the in vitro production of interferon-γ in response to antigens specific for M. tuberculosis
Acid fast stain: can be done directly on samples (sputum). May yield false + due to non-TB mycobacterium.
Active TB culture: Culture sputum in luquid broth 7-14 days. If tubercle bacilli grow, test for antibiotic resistance ~another 6 weeks.
Sensitive nucleic acid amplification: Growing in popularity. Can detect some antibiotic resistances as well.
Pasteurization
Heat to 60oC for 30 minutes
Approximately __% of TB cases worldwide are multidrug resistant
Approximately 7% of TB cases worldwide are multidrug resistant
Source of Borrelia burgdorferi infection
Humans are an accidental host, as B. burgdorferi’s life cycle involves cyclic infection of small mammals and ticks.
____% of patients with latent TB will never develop any disease
90% of patients with latent TB will never develop any disease
Pott disease
Spread of M. tuberculosis infection to vertebral bodies, resulting in chronic back pain. Results more often from secondary tuberculosis.
Progressive Primary Tuberculosis
Occurs when primary TB infection is not controlled. Usually affects the very old, very young, and advanced AIDS patients. Results in progressive pneumonia and possibly bacterial meningitis.
Tuberculosis tree diagram
What stage of the infectious process of B. burgdorferi would be most likely to be directly prevented by a vaccine that elicits antibodies to the OspA protein?
Initial infection!
OspA is expressed on the bacteria within the tick, so very early steps of infection are prevented by antibodies to the protein. The antibodies reach the pathogen when the tick takes a blood meal. OspA is down-regulated when B. burgdorferi enters the human host.
Miliary tuberculosis
Occurs when the primary infection is not contained and tuberculosis invades the bloodstream and disseminates to cause a life-threatening infection.
Results in pockets necrotizing granulomatous inflammation all around the body.
Source of Mycobacterium tuberculosis infection
Almost always acquired from the lung as a result of inhaling particles aerosolized by coughing, sneezing, or talking.
The size of these droplets is ideal for bypassing mucociliary lining. Contageousness roughly correlates to bacterial load. In many cases, the host response to TB creates lung lesions that can contain massive quantities of bacteria.
Treatment of Mycobacterium tuberculosis infection
In any population of tubercle bacilli, mutations associated with resistance to any individual drug are present. Fortunately, the odds that any single oragnism is resistant to two drugs simultaneously are low.
Directly observed therapy for TB has become the standard of care, as regimens are often complicated.
Treatment of latent TB requires only a single drug, as numbers are much lower and less resistant.
Bull’s eye rash. Typical of stage I lyme disease.
Stage III Lyme presentations
Lyme arthritis
Lyme neuritis (pain, numbness, STM loss)
Secondary Tuberculosis pathology
Usually occurs within 2 years of initial infection. Any impairment of the cellular immune system can render a person vulnerable to reactivation of latent mycobacteria. This may include infection with HIV or iatrigenic/procedural immunosuppression. Correlated more or less with specific HLA types. The most common site for reactivation is the apex of the lung.
Results in persistent fever, weight loss, and drenching night sweats. May lead to Pott disease.
Mycobacterium tuberculosis-mediated damage
TB elicits a cellular immune response, with antibodies playing no apparent role. Prevent acidification of the phagolysosome in phagocytes.
Elicits a CD4 response, inducing Type I monocytic inflammation, which typically manifests as necrotizing granulomatous inflammation. Caseous necrosis fluid in the lungs blocks gas exchange. This response often also elicits a Delayed-Type Hypersensitivity to tuberculin.
Persistent acute phase reaction mediated by TNF and IL-1 results in fever, weight loss, and night sweats.
Its waxy coat makes M. tuberculosis resistant to ____, but not ___.
Its waxy coat makes M. tuberculosis resistant to drying, chemicals and killing by phagocytes, but not heat.
Ixodes scapularis
The deer tick
Typically undetected by hosts. If undetected, may feed for 3-5 days continuously. Spirochete transmission does not typically occur until ~day 3. This is because spirochetes are dormant until reanimated by nutrients from tick feeding reperfusing the tick midgut.
