Haemophilus Influenzae Flashcards
What is the gram strain and morphology of H. influenzae?
Gram-negative coccobacillus
T/F. H. influeza is nonmotile and non-spore-forming.
True
What does the genus name Haemophilus mean?
Blood-loving
What two supplements are required for the aerobic growth of H. influenza?
X factor and V factor
This is a heat-stable iron-containing pigment required for H. influenzae to make cytochromes. Provides protoporphyrins, essential for heme biosynthesis.
X factor
This is a heat-labile coenzyme required for metabolic processes. Can be NAD or NADP. Found inside red blood cells.
V factor
Why does H. influenzae exhibit satellitism around colonies of hemolytic S. aureus?
It provides V factor
What are the key characteristics of Haemophilus influenzae colonies?
Granular, transparent (or slightly opaque), circular, and dome-shaped
How do encapsulated strains of H. influenzae appear?
Mucoid and iridescent
Which capsular type is an important invasive pathogen in humans?
Capsular type b
What is H. influenzae’s capsule made of?
Polyribosylribitol phosphate
Why are some H. influenzae strains called nontypeable?
Because they lack a polysaccharide capsule
For which antibody does H. influenzae has a protease?
IgA
T/F. H. influenzae is exclusively recovered from humans.
True
How is Haemophilus influenzae transmitted?
- Airborne droplets
- Direct contact with secretions
What is the first step in Haemophilus influenzae infection leading to otitis media?
Colonization of the upper respiratory tract
What molecules does H. influenzae use to adhere to host cells?
Adhesins
How do type b strains of H. influenzae spread in the body?
They can get access to the bloodstream
How do nontypeable strains of H. influenzae primarily cause disease?
Local invasion of mucosal surfaces
What bacterial components released by H. influenzae trigger host inflammation in otitis media?
- Lipooligosaccharide
- Lipoproteins
- Peptidoglycan fragments
What key virulence genes are more common in otitis media strains of H. influenzae?
- Lipooligosaccharide synthesis gene (lic2B)
- Histidine operon
- Urease operon
What mechanism allows nontypeable H. influenzae to rapidly and reversibly regulate virulence gene expression?
Phase variation (involves methylation of DNA)
What are the most common diseases caused by nontypeable H. influenzae?
- Otitis media
- Sinusitis
- Conjunctivitis
- Tracheobronchitis
- Pneumonia
What are the most common diseases caused by H. influenzae type b?
- Meningitis
- Epiglottitis
- Bacteremia
T/F. Pneumonia caused by H. influenzae type b is now less common due to vaccination.
True
Where is Haemophilus influenzae found in biofilm form?
Middle ear
What part of the respiratory tract is chronically colonized by nontypeable H. influenzae in COPD patients?
Lower respiratory tract
What is the most common bacterial cause of COPD exacerbations?
Nontypeable H. influenzae
In which age group is otitis media most common for nontypeable H. influenzae?
Children aged 6 months to 5 years
What are the symptoms of otitis media in infants?
Fever, irritability and ear pain
Compared to S. pneumoniae, what symptoms are less likely in nontypeable H. influenzae otitis media?
Fever and otorrhea
In which populations is nontypeable H. influenzae a common cause of pneumonia?
- Older adults
- Individuals with COPD
- Those with immunodefficiency
What condition is nontypeable H. influenzae a common cause of in the sinuses?
Acute maxillary sinusitis
What is the most serious acute manifestation of systemic H. influenzae type b infection?
Meningitis
What symptoms often precede H. influenzae type b meningitis?
Upper respiratory infection symptoms
In which adults is H. influenzae type b meningitis more likely to occur?
Those with:
* Recent or remote head trauma
* Prior neurosurgery
* Paranasal sinusitis
* Otitis
* CSF leak
What are the common signs of H. influenzae type b meningitis?
- Fever
- Altered CNS function
Why can nuchal rigidity be absent in young children with H. influenzae type b meningitis?
Because they often lack specific meningeal signs early in the disease.
What complications may develop as H. influenzae type b meningitis progresses?
- Seizures
- Coma
- Subdural effusion
What signs should clinicians look for in older children with H. influenzae type b meningitis?
- Papilledema
- Altered mental status
Acute respiratory obstruction caused by cellulitis of supraglottic tissues, a potentially lethal disease with fulminating onset. Caused by H. influenzae type b.
Epiglottitis
What age group is primarily affected by H. influenzae type b acute respiratory obstruction?
Children aged 2-7 years
What is the characteristic appearance of the epiglottis in H. influenzae type b acute respiratory obstruction?
Cherry red epiglottis
In which age group are primary lung infections by H. influenzae type b most common?
Children aged 4 months to 4 years
During which seasons does H. influenzae type b pneumonia most commonly occur?
Winter or spring
What type of pneumonia does H. influenzae type b typically cause?
Severe consolidative pneumonia
How does H. influenzae type b pneumonia differ from other bacterial pneumonias (e.g., S. aureus, S. pneumoniae)?
- More insidious onset
- Severe dyspnea
- Tachycardia
- Pericarditis
Diagnosis for nontypeable H. influenzae.
Culture
From which samples can microbiologic studies be made to diagnose H. influenzae type b?
- Blood
- CSF
- Other sterile fluids
Active oral antibiotics against nontypeable H. influenzae.
- Amoxicillin-clavulanate
- Fluoroquinolones
- Macrolides
- Cephalosporins
Antibiotics prescribed fot mores serious infections caused by nontypeable H. influenzae.
Parenteral agents:
* Cephalosporins
* Ampicillin-sulbactam
* Fluoroquinolones
First-line regimen for H. influenzae type b.
Cefotaxime or ceftriaxone
T/F. There is currently a conjugated vaccine available for H. influenzae type b.
True
