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Questions and Answers
What is the most common serotype of Haemophilus influenzae found in serious infections?
Which capsule type is unique to H. influenzae type b?
At what age group do the majority of H. influenzae infections occur?
What impact have conjugate vaccines had on H. influenzae type b infections in children?
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Which of the following is NOT classified as a Haemophilus disease state?
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Which age group is most affected by systemic and life-threatening H. influenzae infections?
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What is a common consequence of H. influenzae type b infections in developing countries?
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Which of the following conditions is associated with Haemophilus influenzae infections?
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What does the acronym HACEK stand for in relation to specific bacteria?
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What is the role of the X factor and V factor in the growth of Haemophilus species?
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Which of the following best describes the significance of satellitism in growing Haemophilus?
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Which of the following organisms is identified as a part of the HACEK group?
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How do typeable and non-typeable strains of H.influenzae differ?
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What media components are essential for the growth of Haemophilus species?
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Which trait would best differentiate HACEK organisms from Enterobacteriaceae?
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What is a common disease associated with H.influenzae?
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What condition is associated with genital and perianal ulcers and can cause tender inguinal lymphadenopathy?
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What is the usual outcome of Haemophilus influenzae type b infection in a maternal-fetal context?
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Which characteristic is true for the ulcers caused by Ducreyi?
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Which organism primarily causes endocarditis in young to middle-aged adults?
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What symptom is typical in the early stages of meningitis caused by H.influenzae type b?
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At what age range is epiglottitis most commonly presented?
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What is a common cause of Brazilian purpuric fever?
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What type of infections can occur with pre-existing conditions in association with Ducreyi?
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Which of the following organisms is the most common cause of acute ear infections?
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What is a typical complication of Brazilian purpuric fever?
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What is the relationship between viral sinus infections and bacterial sinusitis?
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In children with H.influenzae meningitis, what other symptoms are commonly present?
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Which condition is most frequently associated with H.influenzae type b?
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Which of the following describes the commonality of H.influenzae in sinusitis cases?
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What is the initial presentation of tracheobronchitis?
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Which type of infections cause more severe symptoms than Haemophilus or S.pneumoniae in sinusitis?
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What type of agar is required for the growth of Aggregatibacter aphrophilus?
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Which virulence factor does Aggregatibacter actinomycetemcomitans produce that affects immune cells?
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What is a clinical condition associated with Aggregatibacter segnis?
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Which feature differentiates Aggregatibacter actinomycetemcomitans from Aggregatibacter segnis?
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What is a common portal of entry for Aggregatibacter actinomycetemcomitans?
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What test result would you expect from Aggregatibacter actinomycetemcomitans in the nitrate reduction test?
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Which of the following statements is true regarding Aggregatibacter segnis?
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Which sugar fermentation result is typically weakly positive for Aggregatibacter segnis?
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Study Notes
HACEK Group
- The HACEK group consists of 6 fastidious Gram-negative bacilli
- These organisms are typically found in the normal upper respiratory tract flora and can cause endocarditis, particularly in individuals with pre-existing valvular heart disease
- HACEK group includes:
- Haemophilus species (H. influenzae, H. parainfluenzae, H. ducreyi)
- Cardiobacterium species (C. hominis, C. valvarum)
- Eikenella corrodens
- Aggregatibacter species (A. aphrophilus, A. paraphrophilus, A. segnis, A. influenzae)
- Kingella species (K. kingae, K. denitrificans)
Haemophilus Species
- Haemophilus species are obligate parasites, meaning they require specific growth factors:
- X factor (haemin)
- Found in blood
- V factor (nicotinamide adenine dinucleotide, NAD)
- Also found in blood
- X factor (haemin)
- Haemophilus species can be differentiated based on their growth requirements and biochemical reactions:
- H. influenzae: requires both X and V factor
- H. parainfluenzae: requires only V factor
- H. ducreyi: does not require X or V factor
- H. influenzae strains are classified into six types (a-f) based on their capsular antigens:
- Type b is the most common serotype associated with serious infections
- Type b is the only serotype with a polyribosyl-ribitol-phosphate (PRP) capsule that contributes to its virulence
- Conjugate vaccines (PRP bound to a protein carrier) have significantly reduced the incidence of H. influenzae type b infections in children
- Common clinical manifestations of Haemophilus infections:
- Meningitis: Most common in children (2-5 years old) although nonencapsulated forms are common in adults
- Epiglottitis: Second most common Haemophilus infection, primarily found in children (2-4 years old)
- Otitis media: S. pneumoniae and H. influenzae are the most common causes of acute ear infections, primarily affecting children (6 months-2 years old)
- Sinusitis: Common in both children and adults
- Upper respiratory tract infections (URIs): Frequently associated with prior influenza virus infections
- Tracheobronchitis: Often caused by H. influenzae and S. ducreyi, characterized by inflammation of the trachea and bronchi
- Pneumonia: H. influenzae type b is the primary cause, while nontypeable H. influenzae is associated with pneumonia in older individuals
- Endocarditis: HACEK group organisms can cause endocarditis, particularly A. aphrophilus
- Bacteremia: Often occurs in the early stages of meningitis and can be linked to dental disease, dog bites or piercings
- Brazilian purpuric fever: Rare, severe and fatal infection caused by a biogroup of H. aphrophilus
Aggregatibacter Segnis
- Frequently found in dental plaque and the upper respiratory tract
- Requires V factor for growth
- Forms greyish-white to opaque colonies on CHOC agar after 48 hours
- Does not grow on SBA
- Positive catalase (variable)
- Negative indole
- Positive ALA-porphyrin test
- Weakly positive for galactose, glucose, maltose, fructose and sucrose fermentation
- Common clinical manifestations:
- Endocarditis
- Periodontal infections
Aggregatibacter Actinomycetemcomitans
- Formerly known as Actinobacillus
- Normal flora of the mouth
- Small, Gram-negative, non-motile coccobacillus
- Requires neither X nor V factor for growth
- Forms star-shaped colonies after 1 week on SBA, CHOC and BHI
- Negative for oxidase, urease, and indole
- Does not ferment lysine, ornithine or arginine
- Ferments glucose, fructose and mannose
- Positive for catalase
- Positive for nitrate reduction
- Common clinical manifestations:
- Abscesses
- Subacute bacterial endocarditis
- Localized juvenile periodontitis
- Virulence factors include a leukotoxin (kills neutrophils, monocytes and T-lymphocytes) and collagenase (toxic to PMNs and monocytes)
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Description
This quiz covers the HACEK group of fastidious Gram-negative bacilli and the specific characteristics of Haemophilus species. It delves into their role in human health, particularly in relation to endocarditis and the unique growth requirements of Haemophilus. Test your knowledge on these important microorganisms and their clinical significance.
