L.6 Haemophilus Flashcards
(44 cards)
What are the clinically significant species of Haemophilus?
H. influenzae, H. ducreyi, H. parainfluenzae
H. parainfluenzae is considered opportunistic
What are the basic characteristics of Haemophilus species?
- Small gram negative coccobacilli
- Part of Upper Resp Tract normal flora
These characteristics are essential for identification and understanding their ecological niche
What are the two types of Haemophilus based on capsule presence?
- Encapsulated
- Non-Encapsulated
Encapsulated strains have serotypes A-F, while non-encapsulated strains are non-typable.
Which serotype of H. influenzae is traditionally associated with most virulent infections?
Serotype b
Serotype b is traditionally associated with 95% of bloodstream and meningeal infections.
What is the role of the capsule in Haemophilus virulence?
Anti-phagocytic properties
The capsule helps the bacteria avoid being engulfed by immune cells.
What are pili and HMW1+2 adhesion proteins used for in Haemophilus species?
Helps the bacteria attach to host cells
This attachment is critical for infection establishment.
What is the function of LOS (lipooligosaccharides) in Haemophilus?
Inhibits mucociliary clearance
This mechanism is utilized by bronchi to remove bacteria from the respiratory tract.
What does IgA protease do in Haemophilus species?
Breaks down IgA
This action helps bacteria evade the immune response.
What is phase variation in Haemophilus?
Ability to change the oligosaccharides expressed on the outer membrane
This adaptation helps bacteria avoid detection by the immune system.
What is the role of biofilm in Haemophilus virulence?
Evade immune defenses and antibiotics
Biofilms protect bacteria from being targeted by the immune system and treatment.
What type of infections do encapsulated strains cause?
Invasive infections including:
* Epiglottitis
* Cellulitis
* BSI (meningitis, osteomyelitis, septic arthritis)
Encapsulated strains are more virulent due to their ability to evade the immune response.
What type of infections do non-encapsulated strains cause?
Mucosal infections including:
* Otitis media
* Sinusitis
* Bronchitis/pneumonia
Non-encapsulated strains are less severe and more common in adults who have developed antibodies.
Why are children more likely to develop invasive infections from encapsulated strains?
Children have no antibodies developed against encapsulated strains.
This lack of immunity makes them more susceptible to serious infections.
What is the most common cause of meningitis in infants aged 6 months to 2 years?
HiB (Haemophilus influenzae type b)
HiB accounts for 50-60% of meningitis cases in this age group.
What is the mortality rate associated with HiB meningitis?
5% mortality rate.
Additionally, 15-30% of cases result in hearing impairments or neurological defects.
When did HiB vaccination become part of the Irish routine immunization programme?
1992.
Since the introduction of the vaccine, there has been a 98% decrease in HiB cases.
What has been observed since 2022 regarding HiB infections?
A slow increase in cases of non-typable and non-typed strains.
This suggests potential changes in epidemiology post-vaccination.
What is the first step in lab investigation for HiB?
Direct specimen - Antigen Detection.
This method allows rapid identification of serious invasive infections.
What method is used for rapid identification of Hib antigens?
Latex agglutination.
Latex beads coated with antisera for serotype b are used.
What type of specimen sample is used for Hib antigen detection?
CSF (Cerebrospinal Fluid).
CSF is the preferred specimen for diagnosing meningitis.
What growth factors are required for in vitro growth of HiB?
Accessory growth factors:
* X factor (haemin) – heat stable
* V factor (NAD) – heat labile
These factors are essential for the cultivation of the organism.
What are the growth conditions for HiB?
Capnophilic - grows in 5-10% CO2, 37°C, for 24-48 hours.
This specific environment is necessary for optimal growth.
What type of agar is required for growing HiB?
Chocolate agar.
Chocolate agar releases V factor and destroys NADase, which is crucial for HiB growth.
