Podcast
Questions and Answers
What type of media is preferred for the culture of Haemophilus ducreyi?
What type of media is preferred for the culture of Haemophilus ducreyi?
Which of the following statements about meningococcal infections is true?
Which of the following statements about meningococcal infections is true?
Which of the following treatment options is NOT effective for chancroid caused by Haemophilus ducreyi?
Which of the following treatment options is NOT effective for chancroid caused by Haemophilus ducreyi?
Which identifying characteristic is associated with Haemophilus aegyptius infections?
Which identifying characteristic is associated with Haemophilus aegyptius infections?
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In the clinical investigation of Haemophilus infections, which specimen is least likely to yield positive results?
In the clinical investigation of Haemophilus infections, which specimen is least likely to yield positive results?
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What is the major virulence factor of Haemophilus influenzae?
What is the major virulence factor of Haemophilus influenzae?
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Which of the following serotypes of Haemophilus influenzae is most commonly associated with invasive disease?
Which of the following serotypes of Haemophilus influenzae is most commonly associated with invasive disease?
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What type of immune response does the anti-PRP antibody facilitate?
What type of immune response does the anti-PRP antibody facilitate?
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What is the recommended method to prevent Haemophilus influenzae type b disease in children?
What is the recommended method to prevent Haemophilus influenzae type b disease in children?
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Which factor is necessary for the growth of Haemophilus influenzae in culture?
Which factor is necessary for the growth of Haemophilus influenzae in culture?
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What age group shows the peak incidence of invasive disease caused by Haemophilus influenzae type b?
What age group shows the peak incidence of invasive disease caused by Haemophilus influenzae type b?
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How does Haemophilus influenzae primarily spread among individuals?
How does Haemophilus influenzae primarily spread among individuals?
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What consequence can occur due to the absence of anti-PRP antibody?
What consequence can occur due to the absence of anti-PRP antibody?
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Study Notes
Haemophilus Species Overview
- Haemophilus species are small, gram-negative, pleomorphic bacteria.
- They require enriched media for growth.
- Includes H. influenzae, H. ducreyi, H. aegyptius, and H. aphrophilus.
Haemophilus influenzae
- Found in the upper respiratory tract of humans.
- Aerobic, small, pleomorphic gram-negative coccobacilli.
- Contains a polysaccharide capsule.
- Six serotypes (a-f) based on capsular polysaccharide antigenicity.
- Type b is responsible for 95% of invasive diseases.
- Type b capsule composed of polyribitol phosphates.
- Unencapsulated/untypeable strains can cause sinusitis and otitis media.
- Growth requires heme (X factor) and nicotinamide adenine dinucleotide (NAD) (V factor).
- Infects only humans.
- Adhesion, colonization, cell damage, and impaired ciliary function are steps in invasion.
- IgA1 protease facilitates colonization.
- Lipid A (from LPS) causes meningeal inflammation.
- Can enter the bloodstream (bacteremia) and spread to meninges.
- Pathogenesis involves anti-phagocytic capsule and endotoxin; no exotoxin.
- Key virulence factor: antiphagocytic polysaccharide capsule (PRP).
- Maternal antibodies provide protection (enhance phagocytosis & complement-mediated bacteriocidal activity).
- Absence of anti-PRP antibody can lead to invasion, bacteremia.
- Peak incidence in children aged 5 months to 1 year.
- Transmission is person-to-person via respiratory route.
- Prevented by Haemophilus b conjugated vaccine.
Haemophilus aegyptius
- Formerly known as Koch-Weeks bacillus.
- Associated with highly contagious conjunctivitis.
- Causes Brazilian purpuric fever in children (fever, purpura, shock, death).
Haemophilus aphrophilus
- Associated with infective endocarditis and pneumonia.
- Part of the normal oral and respiratory tract flora.
Haemophilus ducreyi
- Causes chancroid (sexually transmitted disease).
- Characterized by ragged genital ulcers and swelling.
- Requires X factor but not V factor.
- Treatable with antibiotics (ceftriaxone, trimethoprim-sulfamethoxazole, erythromycin).
Clinical Investigations
- Specimens: Oral swabs (avoid contamination), lower respiratory tract sputum, direct needle aspiration, cerebrospinal fluid (CSF), blood (bacteria count >107/ml).
- Microscopy: Gram-negative bacilli in CSF (before antibiotic treatment) in >80% cases.
- Culture: Chocolate agar preferred (enriched media) with added X and V factors.
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Description
Explore the key characteristics of Haemophilus species, focusing on their classification, growth requirements, and pathogenicity. Learn about significant strains like H. influenzae and their role in human diseases. This quiz covers important aspects of these gram-negative bacteria.
