L22- Human Diseases Caused by Bacteria

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Q: How are airborne bacteria typically transmitted?

A: Aerosolized by infected individuals and inhaled by recipients

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Q: Which organ system is most commonly affected by airborne bacteria?

A: Lungs

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Q: How can airborne bacteria affect organs beyond the lungs?

A: They can enter the bloodstream and spread to other organs

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Q: What type of bacterium is Chlamydia pneumoniae?

A: Gram-negative obligate intracellular parasite

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Q: What infectious form of C. pneumoniae enters the host?

A: Elementary bodies

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Q: What happens to elementary bodies after phagocytosis by host cells?

A: They are retained in inclusion bodies and convert to reticulate bodies

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Q: How long after infection do reticulate bodies begin dividing?

A: ~10 hours

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Q: How long does replication of reticulate bodies last?

A: About 24 hours

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Q: What happens after reticulate bodies replicate?

A: They convert back into elementary bodies and are released

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Q: Common symptoms of Chlamydia pneumoniae infection?

A: Mild pharyngitis, bronchitis, sinusitis, fever, cough, sore throat, laryngitis

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Q: How common are antibodies against C. pneumoniae in adults?

A: ~50% have IgM antibodies

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Q: How long can symptoms persist?

A: Weeks after onset

Q: How is Chlamydia pneumoniae diagnosed?

A: IgM antibody detection and PCR

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Q: First-line treatment for Chlamydia pneumoniae?

A: Macrolides (erythromycin – ribosome target)

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Q: Alternative treatments for Chlamydia pneumoniae?

A: Tetracycline and fluoroquinolones (target gyrase)

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Q: What bacterium causes diphtheria?

A: Corynebacterium diphtheriae

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Q: Gram status and morphology of C. diphtheriae?

A: Gram-positive, highly pleomorphic

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Q: What are volutin granules and why are they important?

A: Cytoplasmic phosphate storage granules; identifying feature of C. diphtheriae

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Q: How is diphtheria transmitted?

A: Nasopharyngeal mucus

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Q: Which organs can diphtheria spread to via the bloodstream?

A: Heart, kidney, nervous system

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Q: Which strains of C. diphtheriae produce toxin?

A: Lysogenic strains carrying the tox gene

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Q: What type of toxin does diphtheria produce?

A: AB exotoxin

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Q: Function of the B subunit of diphtheria toxin?

A: Binds eukaryotic cell receptors and mediates endocytosis

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Q: What happens to diphtheria toxin inside the host cell?

A: Acidification releases the A subunit

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Q: How does the A subunit cause disease?

A: ADP-ribosylates elongation factor-2 → inhibits protein synthesis

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Q: Symptoms of diphtheria?

A: Thick nasal discharge with pus, fever, cough, paralysis

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Q: Cardinal diagnostic sign of diphtheria?

A: Thick gray pseudomembrane on the pharynx

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Q: What staining method identifies volutin granules?

A: Albert stain

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Q: What vaccine prevents diphtheria?

A: Toxoid vaccine (inactivated toxin)

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Q: Diphtheria is most common in which individuals?

A: Non-immunized individuals

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Q: What bacterium causes Legionnaires disease?

A: Legionella pneumophila

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Q: Key structural features of Legionella pneumophila?

A: Gram-negative, rod-shaped, aerobic, fastidious

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Q: Where does Legionella normally reside?

A: Protozoa or amoeba

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Q: How do Legionnaires outbreaks commonly occur?

A: Contaminated air-conditioning water systems

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Q: Is Legionnaires disease spread person-to-person?

A: No

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Q: Where does Legionella reside in humans?

A: Alveolar macrophages

Q: How does Legionella damage host tissue?

A: Cytotoxic exoprotease destroys host tissue

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Q: Who is most at risk for Legionnaires disease?

A: Elderly and immunocompromised individuals

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Q: Symptoms of Legionnaires disease?

A: High fever, cough, headache, dyspnea, bronchopneumonia, diarrhea

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Q: How is Legionnaires disease diagnosed?

A: Isolation of bacteria, antibody detection, antigen in urine

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Q: Treatment for Legionnaires disease?

A: Supportive care + macrolides (azithromycin) or fluoroquinolones

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Q: Mortality rate of Legionnaires disease?

A: Up to 30%

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Q: Which bacteria most commonly cause bacterial meningitis?

A: Streptococcus pneumoniae and Neisseria meningitidis

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Q: Characteristics of Streptococcus pneumoniae?

A: Gram-positive, spherical, facultative anaerobe, diplococcus

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Q: Where is S. pneumoniae normally found?

A: Normal respiratory tract

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Q: Which Neisseria serotypes cause meningitis?

A: A, B, C, Y, W-135

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Q: Which serotype causes outbreaks in Africa?

A: Serotype A

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Q: How do meningitis bacteria enter the CNS?

A: Attach to nasopharynx via pili → bloodstream → blood-brain barrier

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Q: Symptoms of meningitis?

A: Vomiting, headache, lethargy, confusion, stiff neck, purple rash, septic shock

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Q: What tissue is inflamed in meningitis?

A: Brain and spinal cord meninges

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Q: What diagnostic procedure is required for meningitis?

A: Spinal tap

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Q: CSF findings in bacterial meningitis?

A: Low glucose, high leukocytes

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Q: What is aseptic meningitis?

A: Meningitis with no detectable bacteria (often viral/protozoan)

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Q: Primary treatment for bacterial meningitis?

A: Ceftriaxone (3rd-gen cephalosporin – cell wall)

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Q: Alternative treatment if bacteria is sensitive?

A: Penicillin

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Q: Prophylactic treatment for close contacts?

A: Ciprofloxacin

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Q: Members of the TB complex?

A: M. tuberculosis, M. bovis, M. africanum

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Q: Unique structural feature of Mycobacterium?

A: Mycolic acid (waxy outer coat)

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Q: Who discovered TB?

A: Robert Koch

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Q: How many bacteria are needed to cause TB infection?

A: ~10 cells

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Q: Incubation period of TB?

A: 4–12 weeks

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Q: How does TB survive inside macrophages?

A: Blocks lysosomal fusion

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Q: What immune response forms granulomas in TB?

A: Th1 cells and cytotoxic T cells

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Q: Difference between latent and active TB?

A: Latent = contained in granuloma; Active = bacteria released

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Q: Pulmonary symptoms of TB?

A: Chronic cough, chest pain, shortness of breath

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Q: Extrapulmonary TB symptoms?

A: Fever, night sweats, weight loss, lymphadenopathy, headache, confusion

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Q: How is TB diagnosed?

A: Tuberculin skin test + chest X-ray

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Q: What does a positive TB skin test indicate?

A: Prior exposure or vaccination

Q: TB treatment strategy?

A: Combination antibiotic therapy

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Q: Causes of multidrug-resistant TB?

A: Mutations, monotherapy, poor compliance, low doses

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Q: What bacterium causes pertussis?

A: Bordetella pertussis

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Q: Morphology of B. pertussis?

A: Gram-negative coccobacillus

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Q: Mode of transmission of pertussis?

A: Respiratory droplets

Q: Why have pertussis cases increased in the US?

A: Switch from whole-cell to acellular vaccine

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Q: Classic symptoms of pertussis?

A: Severe coughing fits followed by gasping (“whooping cough”)

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Q: Why is pertussis more dangerous in children?

A: Severe disease in unvaccinated children

Q: Mechanism of pertussis AB toxin?

A: ADP-ribosylates Gi → ↑ adenyl cyclase → ↑ cAMP

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Q: Effect of increased cAMP in pertussis?

A: Increased mucin secretion and altered electrolyte balance

Q: Additional toxins produced by B. pertussis?

A: Tracheal cytotoxin, dermonecrotic toxin, nitric oxide

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Q: How is pertussis diagnosed?

A: Culture, PCR, antibody testing

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Q: How is pertussis prevented?

A: Vaccine combined with tetanus and diphtheria (Tdap booster)