hemophilus 2 Flashcards
What specific laboratory technique is used to confirm Haemophilus influenzae type b (Hib) in CSF?
Latex agglutination test for PRP capsular antigen, which is rapid and specific for Hib in CSF and useful even after antibiotic treatment.
How does Haemophilus influenzae evade the immune system in mucosal surfaces?
It produces IgA protease, which degrades IgA antibodies, facilitating colonization on mucosal surfaces by reducing immune detection.
What makes the polysaccharide capsule in Hib critical for its virulence?
The polyribitol phosphate (PRP) component provides resistance to phagocytosis and enhances the bacterium’s invasiveness, particularly in systemic infections.
What is the significance of the Hib capsule’s PRP component in vaccine development?
Conjugated PRP vaccines are used to induce immunity against Hib by creating antibodies specific to PRP, preventing invasive disease.
What factors increase susceptibility to Haemophilus influenzae type b infection?
Patients without anti-PRP antibodies (e.g., infants lacking maternal antibodies), those with immunosuppression, complement deficiency, or asplenia are at higher risk.
How does Haemophilus influenzae type b cause meningitis?
Hib enters through the respiratory tract, crosses into the bloodstream, and can invade the meninges, leading to inflammation and potentially severe complications like deafness.
Which age group is most susceptible to invasive H. influenzae type b (Hib) infections?
Infants and young children under 5 years, especially those under 2, due to immature immune systems and lack of sufficient anti-PRP antibodies.
What role do pili and adhesins play in Haemophilus influenzae infections?
They aid in adherence to the respiratory mucosa, allowing colonization of the nasopharynx and initial stages of infection.
What is the “thumb sign” and its significance in H. influenzae infections?
The “thumb sign” is observed on lateral neck X-rays and indicates swollen epiglottis in cases of Hib-induced epiglottitis, a potentially life-threatening condition.
Why is chocolate agar specifically used for culturing Haemophilus influenzae?
Chocolate agar provides both X (hemin) and V (NAD) factors, which are necessary for the growth of H. influenzae and support the fastidious nature of this bacterium.
How did the introduction of the Hib vaccine impact the incidence of Haemophilus influenzae type b disease?
It dramatically reduced cases of Hib-associated invasive diseases like meningitis and epiglottitis, especially in children.
What is the antibiotic of choice for treating severe H. influenzae type b infections, and why?
Ceftriaxone (or other third-generation cephalosporins), as it penetrates the central nervous system effectively and is bactericidal against H. influenzae.
Describe the satellite phenomenon observed with Haemophilus influenzae on blood agar plates.
H. influenzae grows as satellite colonies around Staphylococcus aureus colonies on blood agar because S. aureus lyses red blood cells, releasing X and V factors that support H. influenzae growth.
Why are non-typeable H. influenzae strains typically less invasive?
Non-typeable strains lack a polysaccharide capsule, which limits their ability to evade immune responses and invade deeper tissues.
What is the clinical significance of non-typeable H. influenzae strains in adults?
They often cause respiratory infections like chronic obstructive pulmonary disease (COPD) exacerbations, otitis media, and sinusitis rather than invasive diseases.
