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Questions and Answers
What is the primary purpose of using PCR techniques in the context of H.influenzae?
What is the primary purpose of using PCR techniques in the context of H.influenzae?
Why is Ceftriaxone considered the first choice antibiotic for serious H.influenzae infections?
Why is Ceftriaxone considered the first choice antibiotic for serious H.influenzae infections?
What is the reason for using a conjugated vaccine for H.influenzae type b?
What is the reason for using a conjugated vaccine for H.influenzae type b?
What is the recommended course of action for household members of a person with serious Hib infection?
What is the recommended course of action for household members of a person with serious Hib infection?
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What age group is particularly encouraged to receive the Hib vaccination due to increased risk?
What age group is particularly encouraged to receive the Hib vaccination due to increased risk?
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What factors are essential for the growth of Haemophilus species in the laboratory?
What factors are essential for the growth of Haemophilus species in the laboratory?
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Which of the following statements about Haemophilus influenzae is correct?
Which of the following statements about Haemophilus influenzae is correct?
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What is the primary antigenic serotype of Haemophilus influenzae responsible for systemic disease?
What is the primary antigenic serotype of Haemophilus influenzae responsible for systemic disease?
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What is the role of the polysaccharide capsule found on some strains of H.influenzae?
What is the role of the polysaccharide capsule found on some strains of H.influenzae?
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How is H.influenzae type b primarily transmitted among humans?
How is H.influenzae type b primarily transmitted among humans?
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What specifically must sheep blood agar undergo to effectively support the growth of Haemophilus species?
What specifically must sheep blood agar undergo to effectively support the growth of Haemophilus species?
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What percentage of healthy individuals may carry non-capsulated strains of H.influenzae in their nasopharynx?
What percentage of healthy individuals may carry non-capsulated strains of H.influenzae in their nasopharynx?
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Which of the following best describes the classification of Haemophilus species?
Which of the following best describes the classification of Haemophilus species?
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What is the peak incidence age for pediatric meningitis caused by H.influenzae type b?
What is the peak incidence age for pediatric meningitis caused by H.influenzae type b?
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Which method is most sensitive for detecting Haemophilus influenzae in CSF specimens?
Which method is most sensitive for detecting Haemophilus influenzae in CSF specimens?
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What is a common laboratory specimen that should not be collected in suspected epiglottitis cases?
What is a common laboratory specimen that should not be collected in suspected epiglottitis cases?
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Which of the following factors are required for the growth of H.influenzae?
Which of the following factors are required for the growth of H.influenzae?
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What is the characteristic odor associated with colonies of H.influenzae on chocolate agar?
What is the characteristic odor associated with colonies of H.influenzae on chocolate agar?
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Which of the following is true about the Quellung reaction?
Which of the following is true about the Quellung reaction?
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What is one of the common serotypes that may share similar antigens with H.influenzae type b?
What is one of the common serotypes that may share similar antigens with H.influenzae type b?
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In which atmosphere should cultures for H.influenzae be incubated?
In which atmosphere should cultures for H.influenzae be incubated?
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What is the primary route of transmission for H. influenzae type b?
What is the primary route of transmission for H. influenzae type b?
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Which virulence factor is most significant for H. influenzae type b?
Which virulence factor is most significant for H. influenzae type b?
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Which clinical condition is not associated with non-invasive H. influenzae type b infection?
Which clinical condition is not associated with non-invasive H. influenzae type b infection?
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Which of the following factors significantly increases the risk of invasive disease caused by H. influenzae type b?
Which of the following factors significantly increases the risk of invasive disease caused by H. influenzae type b?
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How does H. influenzae type b facilitate colonization in the respiratory tract?
How does H. influenzae type b facilitate colonization in the respiratory tract?
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Which component of H. influenzae type b induces meningeal inflammation?
Which component of H. influenzae type b induces meningeal inflammation?
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What is the estimated annual number of fatalities caused by H. influenzae type b in children worldwide?
What is the estimated annual number of fatalities caused by H. influenzae type b in children worldwide?
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Which of the following infections is categorized as invasive caused by H. influenzae type b?
Which of the following infections is categorized as invasive caused by H. influenzae type b?
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Study Notes
Fastidious Bacteria
- Fastidious bacteria require specific nutrients and environmental conditions for growth, making them difficult to cultivate in laboratories.
Haemophilus
- Haemophilus species are small, pleomorphic, gram-negative rods or coccobacilli.
- They are blood-loving, non-motile, and mostly oxidase positive.
- Facultative anaerobes that ferment sugars.
- Require enriched media for isolation, specifically X and/or V factors for growth.
- Grow better in a CO2-enriched environment.
Haemophilus influenzae
- First isolated during the 1918 influenza pandemic by Richard Pfeiffer.
- It is a secondary invader and the first living organism to have its genome fully sequenced.
- Requires haemin (X factor) for the synthesis of cytochrome C and other iron-containing enzymes.
- Also requires nicotinamide adenine dinucleotide NAD(P) (V factor) essential for oxidation-reduction processes in cellular metabolism.
- Both X and V factors are present in blood-enriched media.
Haemophilus influenzae capsule
- The capsule is a major virulence factor in Haemophilus influenzae.
- Six antigenic serotypes (a-f) with type b being the most virulent, containing polyribitol phosphate (PRP) in the capsule.
- Antibodies against the capsule enhance phagocytosis and complement-mediated bactericidal activity.
- These antibodies are acquired through natural infection, vaccination with purified PRP, or passive transfer of maternal antibodies.
Haemophilus influenzae epidemiology
- Exclusively found in humans, primarily in the respiratory tract.
- No animal or environmental reservoirs.
- Non-capsulated strains colonize the nasopharynx or throat in 25-80% of healthy individuals.
- Capsulated strains (half are type b) are found in 5-10%.
- H. influenzae type b was the leading cause of systemic disease in children before the vaccine.
- After the vaccine, other serotypes of encapsulated bacteria and non-encapsulated strains became more prevalent.
Haemophilus influenzae pathogenesis
- Transmitted through respiratory droplets or direct contact with contaminated secretions.
- Enters the body through the upper respiratory tract, colonizing asymptomatically or causing infections like sinusitis, otitis media, or pneumonia.
- Produces IgA protease that degrades secretory IgA, facilitating its attachment to the respiratory mucosa.
- Encapsulated organisms can invade blood capillaries directly and reach the meninges.
- Nontypable strains, although less invasive, also induce an inflammatory response causing disease.
- No exotoxins are produced.
- Outbreaks are common in nurseries and childcare centers.
Haemophilus influenzae virulence factors
- Pili and non-pilus adhesins mediate colonization of the oropharynx with H. influenzae.
- Cell wall components like lipopolysaccharide and glycopeptide impair ciliary function, damaging the respiratory epithelium.
- PrP capsule is a major virulence factor in H. influenzae type b.
- Lipopolysaccharide lipid A component induces meningeal inflammation.
- Immunoglobulin IgA1 proteases are produced by both encapsulated and non-encapsulated strains, interfering with humoral immunity and facilitating colonization.
Haemophilus influenzae clinical diseases
- Invasive infections: meningitis, epiglottitis, pneumonia, cellulitis, septic arthritis, and osteomyelitis.
- Non-invasive infections: otitis media, sinusitis, acute exacerbation of COPD, and conjunctivitis.
Risk factors for Haemophilus influenzae invasive disease
- Lack of anti-PRP antibodies
- Complement depletion
- Splenectomy
- Immunosuppression
- Hypogammaglobuliemia
Haemophilus influenzae Meningitis
- Formerly the most common cause of pediatric meningitis.
- Peak incidence between 3 to 18 months.
- More prevalent during winter months.
- Increased risk among household contacts of cases under 5 years, especially those under 6 months.
- High case fatality rate.
Laboratory diagnosis of Haemophilus influenzae
- Specimens include CSF, sputum, blood, joint, or pleural fluid.
- Meningitis: blood and CSF.
- Epiglottitis, cellulitis, and arthritis: blood cultures.
- Avoid posterior pharyngeal swabs in patients with suspected epiglottitis to prevent coughing and airway obstruction.
Haemophilus influenzae microscopy
- Sensitive and specific method.
- Detected in over 80% of CSF specimens from patients with untreated Haemophilus meningitis.
Haemophilus influenzae antigen detection
- Rapid latex agglutination test is rapid and sensitive.
- Detects less than 1 ng/ml of PRP capsular antigen in clinical specimens.
- Specific to H. influenzae type b.
- Useful in specimens taken after antibiotic treatment, but cross-reactivity with other serotypes of S. pneumoniae and E. coli is possible.
Haemophilus influenzae culture
- Chocolate agar (overheating destroys V factor) is used.
- Incubated in an aerobic atmosphere enriched with 5-10% CO2.
- 1-2mm smooth, opaque colonies appear after 24 hours.
- Emits a "mousy" or "bleach-like" odor.
- Blood cultures are delayed and may not contain optimal X and V factor concentrations.
Haemophilus influenzae identification
- Identification is based on growth on nutrient agar with V, X, and XV factors.
- H. influenzae requires both X and V factors.
- H. parainfluenzae requires V factor alone.
- H. ducreyi requires X factor alone.
Additional Haemophilus influenzae tests
- Quellung reaction (capsule swelling test): antibodies bind to the capsule, making it opaque and enlarged under a microscope. Specific for H. influenzae type b.
- Satellite phenomenon: H. influenzae grows around colonies of S. aureus on blood agar, lysing red blood cells and releasing X factor and V factor.
- PCR techniques: used to identify Haemophilus species in clinical specimens and confirm isolate identification.
- Capsular type determination: slide agglutination or PCR.
Haemophilus influenzae treatment
- Mortality rate in untreated meningitis or epiglottitis approaches 100%.
- Serious infections are treated with third-generation cephalosporins like ceftriaxone.
- Less severe infections, like sinusitis and otitis, can be treated with oral antibiotics like amoxicillin, azithromycin, or clarithromycin.
Haemophilus influenzae prevention and control
- Vaccination: purified PRP conjugated (protein carrier) vaccine is given at 2, 3, and 4 months. It is highly effective in reducing H. influenzae type b disease and colonization.
- Antibiotic prophylaxis: Rifampin orally once daily for 4 days eradicates H. influenzae carriage.
- Household members of individuals with serious Hib infection at increased risk, particularly children based on age and those with splenic dysfunction.
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Description
This quiz covers the unique characteristics of fastidious bacteria, with a focus on Haemophilus species. Explore their growth requirements, historical significance, and metabolic needs essential for laboratory cultivation. Test your knowledge on the specific nutrients and conditions these organisms require for isolation.
