Podcast
Questions and Answers
Why does Legionella pneumophila require a specialized growth medium containing high concentrations of iron and L-cysteine?
Why does Legionella pneumophila require a specialized growth medium containing high concentrations of iron and L-cysteine?
- These nutrients are essential for the bacterium's metabolic pathways and enzyme function, which cannot be synthesized otherwise. (correct)
- These substances are needed to facilitate the bacterium's entry into host cells by mimicking host cell surface receptors.
- The bacterium uses iron and L-cysteine to neutralize reactive oxygen species produced by the host's immune cells.
- These components are required for the synthesis of the bacterium's protective capsule, which is essential for its survival in the host.
How does the intracellular lifestyle of Legionella pneumophila contribute to the pathogenesis of Legionnaires' disease?
How does the intracellular lifestyle of Legionella pneumophila contribute to the pathogenesis of Legionnaires' disease?
- Intracellular proliferation allows the bacteria to evade detection by antibiotics, making treatment more challenging.
- Intracellular survival promotes the secretion of toxins that directly damage the lung tissue, causing acute respiratory distress.
- The intracellular niche protects the bacteria from antibody-mediated neutralization and complement-mediated lysis. (correct)
- Replication within macrophages prevents the activation of the adaptive immune response, leading to chronic infection.
Why is urinary antigen testing a useful diagnostic tool for Legionnaires' disease?
Why is urinary antigen testing a useful diagnostic tool for Legionnaires' disease?
- The test identifies volatile organic compounds released by _Legionella_ in the lungs that are excreted in the urine.
- The test identifies specific antibodies produced by the host in response to _Legionella_ infection, indicating prior exposure.
- The test measures the level of _Legionella_ DNA in the urine, providing a quantitative assessment of the bacterial load.
- The test detects a unique _Legionella_ antigen that is shed into the urine during active infection, even before pneumonia is evident on X-rays. (correct)
What is the significance of observing numerous neutrophils but no bacteria on a Gram stain of a clinical sputum sample from a patient suspected of having Legionnaires' disease?
What is the significance of observing numerous neutrophils but no bacteria on a Gram stain of a clinical sputum sample from a patient suspected of having Legionnaires' disease?
What is the most critical factor that differentiates Legionnaires' disease from Pontiac fever, both caused by Legionella pneumophila?
What is the most critical factor that differentiates Legionnaires' disease from Pontiac fever, both caused by Legionella pneumophila?
Why are individuals with AIDS at an elevated risk of contracting Legionnaires' disease?
Why are individuals with AIDS at an elevated risk of contracting Legionnaires' disease?
Why is beta-lactam antibiotic monotherapy generally ineffective against Legionella pneumophila?
Why is beta-lactam antibiotic monotherapy generally ineffective against Legionella pneumophila?
What is the role of amoebas in the transmission and pathogenesis of Legionella pneumophila?
What is the role of amoebas in the transmission and pathogenesis of Legionella pneumophila?
How does Legionella pneumophila induce hyponatremia in infected individuals, and what is the underlying mechanism?
How does Legionella pneumophila induce hyponatremia in infected individuals, and what is the underlying mechanism?
Why is it important to consider environmental sampling and testing when investigating potential outbreaks of Legionnaires' disease, rather than relying solely on clinical diagnostics?
Why is it important to consider environmental sampling and testing when investigating potential outbreaks of Legionnaires' disease, rather than relying solely on clinical diagnostics?
Flashcards
Legionella pneumophilia
Legionella pneumophilia
Causes Legionnaire’s disease, leading to atypical pneumonia in immunocompromised individuals. Requires iron and L-cysteine for growth.
Legionella Risk Factors
Legionella Risk Factors
Older men who smoke/drink heavily, cancer, AIDS, transplant recipients, or those on corticosteroids.
Legionella Transmission
Legionella Transmission
Air conditioners, water towers, hospital water taps/showers. Transmission via inhalation of aerosolized organisms.
Pontiac Fever
Pontiac Fever
A mild, flu-like form of Legionella infection that does NOT cause pneumonia.
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Legionella Diagnosis
Legionella Diagnosis
Hyponatremia, clinical sputum with neutrophils but no bacteria on Gram stain, urinary antigen test.
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Legionella Treatment
Legionella Treatment
Azithromycin, erythromycin (±rifampin), levofloxacin, or trovafloxacin.
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- Legionella pneumophilia causes Legionnaire’s disease, an atypical pneumonia, mainly in immunocompromised individuals, and shows as bilateral interstitial opacities on X-ray.
- High-risk groups include older men who smoke, consume alcohol, individuals with cancer or AIDS, transplant recipients, and those on corticosteroids.
- It necessitates a high iron and L-cysteine concentration to grow.
- Gram-negative, facultative intracellular, obligate aerobe, pleomorphic bacilli, unencapsulated, and possesses endotoxin (LPS).
- Spreads via environmental water sources like air conditioners and water towers or hospital water systems, transmission occurs through inhaling organisms aerosolized within amoebas.
- Person-to-person transfer does not occur.
- Mental confusion may arise as a symptom.
- Nonbloody diarrhea may occur.
- Microscopic hematuria and proteinuria may also occur.
- A cough arises that yields nonpurulent sputum.
- Legionella usually resolves spontaneously in 7 to 10 days.
- It can be fatal in immunocompromised individuals.
- Pontiac fever, a mild, flu-like form, derived its name from Pontiac, Michigan (site of a 1968 outbreak) and does not result in pneumonia
- Notable findings include hyponatremia, clinical sputum with neutrophils but no visible bacteria (on regular stains), and growth on special yeast agar after 3-5 days, with a positive urinary antigen test.
- Azithromycin or erythromycin (with/without rifampin) OR levofloxacin and trovafloxacin are the treatments of choice.
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