Haemophilus, Bordetella, Brucella Flashcards
(49 cards)
General characteristics of Haemophilus
◾ Gram-negative coccobacilli
◾ facultative anaerobes
◾ non-motile
◾ non-sporing
◾ oxidase positive
◾ catalase positive
Briefly discuss Haemophilus accessory growth factors.
(1) Factor X (Hemin): This is porphyin compound [similar to haem]. It is required for the synthesis of cytochrome and other enzymes e.g. catalase, peroxidase and oxidase. It is heat stable.
(2) Factor V (NAD or NADP): These are hydrogen acceptors in cellular metabolism. They are heat labile (destroyed at 120°C).
Briefly discuss Haemophilus virulence factors.
✔ Capsule: contains PRP (polyribosyl-ribitol phosphate), which prevents phagocytosis and opsonisation. This is the main virulence factor.
✔ Pili; adherence factor
✔ Outer membrane proteins e.g. porins, adhesins
✔ Lipooligosaccharide; may trigger strong inflammatory response
✔ IgA protease
How are Haemophilus influenzae serotypes classified?
H. influenzae strains are broadly classified as either:
(1) Encapsulated: These are further classified into six serotypes (a-f) based on the capsular polysaccharide. [These serotypes are not considered strains.]
(2) Non-encapsulated (NTHi): These lack a capsule and are not classified into serotypes.
✔ Strains: Both encapsulated (within a serotype) and non-encapsulated H. influenzae can be further classified into strains. Strains are defined primarily by genetic differences.
✔ Biotype: strains are futher subdivided into 8 biotypes (I-VIII) based on biochemical characteristics: urease activity, ornithine decarboxylase activity, and indole production.
Comment briefly on the epidemiology of H. influenzae.
◾ Mucosal organism spread through respiratory droplets.
◾ Present in 30-50% of healthy persons.
◾ Infections are seen frequently in children aged from six months to 4 years of age.
◾ In adults, it may produce secondary complications of severe primary illnesses.
◾ Immunocompromised adults are also at risk of developing infections.
Which Haemophilus influenzae serotype is responsible for majority of invasive diseases?
serotype b
Where is NTHi commonly found?
normal microbial flora of the upper respiratory tract
What types of infections are most commonly associated with NTHi?
It is usually involved in respiratory tract infections in children, otitis media, sinusitis, bronchitis and pneumonia.
Briefly describe the key steps in the pathogenesis of Haemophilus influenzae.
(1) H. influenzae attaches to the respiratory mucosa using adhesins and pili.
(2) The bacteria evade the host’s immune response via:
✔ IgA proteases (degrade IgA antibodies)
✔ Microcolony formation
✔ Phase/Antigenic variation (changes in surface antigens)
✔ Intracellular survival/invasion (in some cases)
(3) Encapsulated strains resist phagocytosis due to their capsule, allowing them to enter the bloodstream and cause invasive infections like, meningitis, epiglottitis, and septicaemia.
appropriate specimens for laboratory investigation of H. influenzae
Depends on the type of infection:
✔ Meningitis: CSF
✔ Epiglottitis: blood
✔ Pneumonia: sputum/tracheal aspirates
✔ Others: joint fluid, pleural fluid, middle ear fluid
State the most suitable agar for culturing of H. influenzae, and explain why it is preferred over other media.
Chocolate blood agar (CBA)
CBA is a nutrient agar enriched with heated blood, which releases Factor X and Factor V, making them available for the bacteria to grow.
Further notes:
Blood agar: While it contains blood, the red blood cells remain intact, and Factor X is not readily available. H. influenzae may grow on blood agar only as tiny satellite colonies around other bacteria that can lyse the red blood cells and release Factor X.
MacConkey agar: This is a selective medium for gram-negative bacteria, but it does not provide the necessary growth factors for H. influenzae.
What is the basis of the satellitism test for identifying Haemophilus influenzae?
◾ The satellitism test relies on the fact that H. influenzae requires specific growth factors, primarily NAD (nicotinamide adenine dinucleotide or Factor V), which it cannot produce on its own.
◾ Staphylococcus aureus produces NAD as a byproduct of its metabolism.
◾ Therefore, when the two bacteria are co-cultured, H. influenzae will grow as small “satellite” colonies only near the S. aureus streak.
[Image 1] [Image 2]
main prevention method against H. influenzae
Vaccination. Currently the only available H. influenzae vaccine is the Hib vaccine.
What is Haemophilus influenzae biogroup aegyptius (Hae), and what is its primary clinical manifestation?
◾ Hae is a biogroup of non-typeable H. influenzae (NTHi) with a strong predilection for the conjunctiva.
◾ Its primary clinical manifestation is acute purulent conjunctivitis, a contagious eye infection characterized by pus discharge, often occurring in seasonal epidemics.
Besides conjunctivitis, what other, less common, disease is associated with Haemophilus influenzae biogroup aegyptius?
Brazilian Purpuric Fever: conjunctivitis, high fever, haemorrhagic skin lesions, abdominal pain, nausea, vomiting, septic shock, death [Image]
Briefly discuss clinical implications of Haemophilus ducreyi infection.
◾ Causative agent of chancroid: a sexually transmitted ulcer
◾ May cause lymphadenitis and bubo [large, tender lymph nodes in the groin] formation
◾ Can spread to other sites through autoinoculation
Progression and clinical presentation of chancroid
✔ Tender erythematous papule: The initial lesion usually appears as a small, red, and tender bump (papule) at the site of infection [4-7 days after exposure to H. ducreyi].
✔ Papule develops into a pustule
✔ Pustule ruptures within 2-3 days, forming a painful, shallow ulcer
✔ The ulcer has a soft, raised border, and a base covered with a grayish or yellowish, pus-like exudate
common sites for chancroid lesions in men and women
List the HACEK organisms.
◾ Haemophilus species [other than H. influenzae]
◾ Aggregatibacter species
◾ Cardiobacterium hominis
◾ Eikenella corrodens
◾ Kingella species
What do the HACEK organisms have in common?
◾ They are all part of the normal flora of the oral cavity.
◾ They are opportunistic microorganisms; require immunocompromised host.
◾ They can enter the bloodstream and cause infection, particularly in people with damaged heart valves or other underlying health conditions.
◾ The are responsible for 3% of cases of infective endocarditis, and are often a cause of culture-negative endocarditis.
3 clinically relevant Bordetella species
✔ Bordetella pertussis
✔ Bordetella parapertussis
✔ Bordetella bronchiseptica
general characteristics of Bordetella
◾ small, Gram-negative coccobacilli
◾ strict aerobes
◾ non-motile [B. bronchiseptica is motile]
◾ capsulated
◾ non-spore forming
Bordetella virulence factors
(1) Adhesins: filamentous haemagglutinin (FHA), pertactin, fimbriae
(2) Toxins: pertussis toxin, adenylate cyclase (CyaA) toxin, dermonecrotic toxin, tracheal cytotoxin
(3) Secretion systems: Type III secretion system, Type IV secretion system
Make a brief note on the important virulence secretion systems in Bordetella.
✔ Type III secretion system: Bordetella species possess a T3SS, a needle-like structure that allows them to inject effector proteins directly into the cytoplasm of host cells.
✔ Type IV secretion system: The T4SS forms a channel through which PT is transported across the bacterial outer membrane.
