HACEK Group and Haemophilus Species

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Questions and Answers

What is the most common serotype of Haemophilus influenzae found in serious infections?

Type d

Type c

Type b (correct)

Type a

Which capsule type is unique to H. influenzae type b?

Polyribosyl-ribitol-phosphate (PRP) capsule (correct)

Polysaccharide capsule

Polyglycerol phosphate capsule

Polyethylene glycol capsule

At what age group do the majority of H. influenzae infections occur?

Elderly above 65 years

Adults aged 18 to 40 years

Newborns up to 2 months

Children aged 2 months to 5 years (correct)

What impact have conjugate vaccines had on H. influenzae type b infections in children?

Dramatically lowered infection rates Signup and view all the answers

Which of the following is NOT classified as a Haemophilus disease state?

Bronchitis Signup and view all the answers

Which age group is most affected by systemic and life-threatening H. influenzae infections?

Infants under 2 years Signup and view all the answers

What is a common consequence of H. influenzae type b infections in developing countries?

Bacterial pneumonia deaths and meningitis Signup and view all the answers

Which of the following conditions is associated with Haemophilus influenzae infections?

Chancroid Signup and view all the answers

What does the acronym HACEK stand for in relation to specific bacteria?

Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella Signup and view all the answers

What is the role of the X factor and V factor in the growth of Haemophilus species?

X factor is hemin and V factor is nicotinamide adenine dinucleotide. Signup and view all the answers

Which of the following best describes the significance of satellitism in growing Haemophilus?

It requires the presence of nearby bacteria that provide V factor. Signup and view all the answers

Which of the following organisms is identified as a part of the HACEK group?

Eikenella corrodens Signup and view all the answers

How do typeable and non-typeable strains of H.influenzae differ?

Typeable strains possess a capsule, while non-typeable strains lack one. Signup and view all the answers

What media components are essential for the growth of Haemophilus species?

Blood agar and enrichment broth Signup and view all the answers

Which trait would best differentiate HACEK organisms from Enterobacteriaceae?

Distinct colony morphology and biochemical reactions Signup and view all the answers

What is a common disease associated with H.influenzae?

Meningitis Signup and view all the answers

What condition is associated with genital and perianal ulcers and can cause tender inguinal lymphadenopathy?

Chancroid Signup and view all the answers

What is the usual outcome of Haemophilus influenzae type b infection in a maternal-fetal context?

Bacteremia Signup and view all the answers

Which characteristic is true for the ulcers caused by Ducreyi?

Gray to yellowish exudate Signup and view all the answers

Which organism primarily causes endocarditis in young to middle-aged adults?

HACEK organisms Signup and view all the answers

What symptom is typical in the early stages of meningitis caused by H.influenzae type b?

High fever Signup and view all the answers

At what age range is epiglottitis most commonly presented?

2 years to 4 years Signup and view all the answers

What is a common cause of Brazilian purpuric fever?

One biogroup of Haemophilus Signup and view all the answers

What type of infections can occur with pre-existing conditions in association with Ducreyi?

Opportunistic infections Signup and view all the answers

Which of the following organisms is the most common cause of acute ear infections?

S.pneumoniae Signup and view all the answers

What is a typical complication of Brazilian purpuric fever?

Hypotensive shock Signup and view all the answers

What is the relationship between viral sinus infections and bacterial sinusitis?

Bacterial sinusitis usually stems from viral sinus infections. Signup and view all the answers

In children with H.influenzae meningitis, what other symptoms are commonly present?

Symptoms of upper respiratory infection and otitis media Signup and view all the answers

Which condition is most frequently associated with H.influenzae type b?

Pneumonia Signup and view all the answers

Which of the following describes the commonality of H.influenzae in sinusitis cases?

It is frequently the cause of sinusitis in both children and adults. Signup and view all the answers

What is the initial presentation of tracheobronchitis?

Chronic bronchitis Signup and view all the answers

Which type of infections cause more severe symptoms than Haemophilus or S.pneumoniae in sinusitis?

Anaerobic infections Signup and view all the answers

What type of agar is required for the growth of Aggregatibacter aphrophilus?

Chocolate agar Signup and view all the answers

Which virulence factor does Aggregatibacter actinomycetemcomitans produce that affects immune cells?

Leukotoxin Signup and view all the answers

What is a clinical condition associated with Aggregatibacter segnis?

Dental plaque and upper respiratory tract infections Signup and view all the answers

Which feature differentiates Aggregatibacter actinomycetemcomitans from Aggregatibacter segnis?

The requirement for V factor Signup and view all the answers

What is a common portal of entry for Aggregatibacter actinomycetemcomitans?

Urinary tract instrumentation Signup and view all the answers

What test result would you expect from Aggregatibacter actinomycetemcomitans in the nitrate reduction test?

Positive Signup and view all the answers

Which of the following statements is true regarding Aggregatibacter segnis?

It is a pleomorphic rod. Signup and view all the answers

Which sugar fermentation result is typically weakly positive for Aggregatibacter segnis?

Maltose Signup and view all the answers

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
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.