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Which method is commonly used to assess the toxigenicity of bacteria?
Which biomarker may indicate a worse prognosis in a patient?
Which of the following conditions closely mimics Corynebacterium diphtheria?
Who is at increased risk for contracting diphtheria?
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What is the primary method of preventing diphtheria?
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What is the primary agent responsible for causing tuberculosis?
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Which of the following symptoms is NOT typically associated with active tuberculosis?
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What is the characteristic structure of the cell wall of Mycobacterium species?
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How long does the cell division of Mycobacterium tuberculosis take?
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What is the primary symptom associated with diphtheria?
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What role does mycolic acid play in Mycobacterium tuberculosis?
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Which fragment of the diphtheria toxin is responsible for inhibiting protein synthesis?
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Which of the following antibiotics is NOT typically used in the treatment of tuberculosis?
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What type of bacteria is Corynebacterium diphtheriae?
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What is the main reason for the use of multiple antimicrobial drugs in tuberculosis treatment?
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Which of the following substances is particularly required for the growth of Corynebacterium diphtheriae?
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Which diagnostic method is most commonly used for identifying tuberculosis?
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What characterizes toxigenic strains of Corynebacterium diphtheriae?
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What are the biotypes of Corynebacterium diphtheriae based on?
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How does diphtheria toxin affect eukaryotic cells?
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What is the purpose of immunization with diphtheria toxoid?
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What is a primary factor limiting patient compliance with tuberculosis treatment?
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What does MDR-TB stand for?
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Which of the following conditions is NOT caused by systemic miliary tuberculosis?
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What is the primary virulence factor of Mycobacterium tuberculosis?
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Why is the BCG vaccine not widely used in the United States?
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What is the role of directly observed therapy (DOT) in tuberculosis treatment?
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What type of organism is Mycobacterium leprae?
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What is a common factor affecting the clinical course of leprosy?
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Study Notes
Mycobacterium tuberculosis
- Mycobacterium tuberculosis is a slow-growing, aerobic, acid-fast bacterium that causes tuberculosis.
- Tuberculosis is a chronic, progressive infection that primarily affects the lungs.
- M. tuberculosis is a weakly gram-positive, non-motile, rod-shaped bacterium.
- It is an obligate aerobe and a facultative intracellular parasite. This explains why tuberculosis typically affects the lungs.
- The cell wall of mycobacterium is primarily composed of lipids. The lipid layer makes it impervious to gram staining, resulting in a variable gram reaction.
- M. tuberculosis has a slow generation time (18-24 hours) due to the mycolic acid layer in its cell wall, which inhibits nutrient diffusion and protects it from immune cells.
- Symptoms of active TB include: coughing (lasting more than 3 weeks), coughing up blood, chest pain, unintentional weight loss, fatigue, fever, night sweats, chills, and loss of appetite.
- Antibiotic treatment involves a combination therapy with isoniazid (INH), rifampin (RIF), pyrazinamide (PZA), ethambutol (EMB), or streptomycin (SM) for at least 4 months.
- Treatment of M. tuberculosis can be challenging due to its slow growth rate, the long treatment duration (6-9 months), and potential side effects of the antibiotics.
- Directly observed therapy (DOT) is used to ensure patient compliance.
- Antibiotic resistance is a concern, with multi-drug resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) strains emerging.
- A BCG vaccine is available but is not particularly effective and is not used in the United States.
- M. tuberculosis does not produce toxins or exoenzymes that damage tissue. The protective waxes in the cell wall are its primary virulence factor.
- Damage caused by tuberculosis stems from the immune response to the bacteria.
- Systemic miliary tuberculosis can spread causing: meningitis, sterile pyuria, Pott's disease (spinal tuberculosis), Addison's disease, hepatitis, and lymphadenitis.
Mycobacterium leprae
- Mycobacterium leprae and Mycobacterium lepromatosis cause leprosy.
- Leprosy is an obligate intracellular organism that parasitizes histiocytes (skin macrophages) and Schwann cells in the peripheral nerves.
- Multidrug therapy is available for treating leprosy, but some patients experience relapses or prolonged symptoms.
- Immune responses to bacterial components influence the range of symptoms.
Corynebacterium diphtheriae
- Corynebacterium diphtheriae infects the nasopharynx or skin.
- Toxigenic strains produce a potent exotoxin causing diphtheria.
- Diphtheria symptoms include pharyngitis, fever, swelling of the neck or skin lesion.
- Diphtheritic lesions are covered by a pseudomembrane.
- The toxin can spread through the circulatory system, impacting distant organs and leading to paralysis and congestive heart failure.
- Corynebacterium diphtheriae is a nonmotile, noncapsulated, club-shaped, gram-positive bacillus.
- Toxigenic strains are lysogenic for corynebacteriophages carrying the gene for diphtheria toxin.
- C. diphtheriae biotypes include mitis, intermedius, and gravis, classified based on colony morphology and lysotype.
- Optimal diphtheria toxin production requires a medium supplemented with amino acids and low iron content.
- Asymptomatic nasopharyngeal carriage is common in endemic regions.
- In susceptible individuals, toxigenic strains multiply and secrete diphtheria toxin in nasopharyngeal or skin lesions.
- The diphtheritic lesion is often covered by a pseudomembrane.
- Diphtheria toxin is cleaved into two fragments: Fragment A (catalytic domain) and Fragment B (transmembrane and receptor binding domains).
- Fragment A inhibits protein synthesis in eukaryotic cells by ADP-ribosylation of elongation factor 2.
- Fragment B binds to cell surface receptors to deliver Fragment A to the cytosol.
- Protection against diphtheria involves antibody responses to diphtheria toxin or toxoid (formaldehyde-inactivated toxin).
- Diagnosis relies on culture-proven toxigenic C. diphtheriae infection in the skin, nose, or throat, and clinical signs of nasopharyngeal diphtheria.
- Toxigenicity is identified by in vitro or in vivo methods.
- Elevated biomarkers like total leukocyte count and serum glutamic oxalo-acetic transaminase levels (SGOT) can indicate a worse prognosis and correlate with disease severity.
- Corynebacterium diphtheria has many similarities with other diseases, such as viral pharyngitis, streptococcal pharyngitis, acute epiglottitis, infectious mononucleosis, oral candidiasis, infective endocarditis, angioedema, epiglottitis, and retropharyngeal abscess.
- Risk of diphtheria is higher in unvaccinated children and adults, people living in crowded conditions, and people travelling to areas with high diphtheria prevalence.
- Antibiotics like penicillin or erythromycin help clear up infections.
- Antitoxin is used to counteract diphtheria toxin in the body.
- Immunization with diphtheria toxoid is highly effective.
- Diphtheria patients require prompt treatment with antitoxin to neutralize circulating toxin.
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Description
This quiz explores the characteristics, symptoms, and treatment of Mycobacterium tuberculosis, the bacterium responsible for tuberculosis. It covers the bacterium's biology, including its classification as a slow-growing and aerobic microorganism, and the impact of its lipid-rich cell wall on antibiotic resistance. Test your knowledge on this significant public health issue.
