Hemophilus Flashcards
general characterstics?
Haemophilus= blood loving
Gram-negative coccobacilll
Non-motile
Non-sporing
Facultative anaerobes
Oxidase positive
Catalase positive
accessory growth factors
X Factor (Haemin)
• A component of the iron-containing part of hemoglobin.
• Heat stable.
• Helps make cytochrome and enzymes like catalase, peroxidase, and oxidase.
V Factor (NAD/NADP)
• Acts as a hydrogen acceptor in metabolism.
• Heat labile (destroyed at 120°C).
• Found inside red blood cells (RBCs).
• Some fungi and bacteria can produce it.
Haemophilus influenzae – X & V Factors
Requires X factor (Hemin) & V factor (NAD) for growth
Grows on chocolate agar (not blood agar)
Causes respiratory infections, meningitis, otitis media
Encapsulated strains (e.g., type b, Hib) are more virulent
Virulence factors?
Capsule
-Contains PRP (polyribosyl-ribitol phosphate) – prevents phagocytosis and opsonisation
-Main virulence factor
Adhesion proteins
Outer membrane proteins
IgA₁ protease – H. influenzae
Lipooligosaccharide (LOS)
Epidemiology
Mucosal organism
Spread by airborne droplets and contact with secretions
H. influenzae infections are seen frequently in children aged 6m-4yrs
in adults: 2nd complications of severe 1° illness
Which serotype causes majority of disease?
H.influenza type b
Pathogenesis
Pathogenesis of Haemophilus influenzae
- Mucociliary Interactions
H. influenzae disrupts normal mucociliary clearance, helping it colonize the respiratory tract.
- Attachment to Respiratory Mucosa
Adhesins: Surface proteins that help the bacteria attach to epithelial cells.
Pili: Hair-like structures that enhance bacterial adherence to host tissues.
- Evasion of Mucosal Immunity
Proteases: Includes IgA₁ protease, which degrades host IgA, weakening mucosal immunity.
Microcolony Formation: Clusters of bacteria protect against immune attack.
Phase Variation/Antigenic Shift: Allows H. influenzae to alter its surface antigens, avoiding immune recognition.
Intracellular Survival/Invasion: Some strains invade epithelial cells and survive inside host tissues, contributing to chronic infections.
This combination of strategies makes H. influenzae a significant pathogen in respiratory infections, including otitis media, pneumonia, and meningitis (especially type b, Hib).
Examples of localised infections caused by (non-encapsulated) strains
otitis media
pneumonia
Examples of invasive infections? (caused by capsulated strains)
meningitis
epiglottitis
septicemia
Specimen?
CSF, blood, pus aspirates,
Microscopic examination? (gram stain)
Gram stain: very small pleomorphic gram-negative coccobacilli or rod
Capsule surrounding rod may be observed
https://images.app.goo.gl/nF4hjgzsZagfbM1c8
Culture? (media and appearance)
Chocolate agar
Semi-opaque, gray-white, convex, mucoid colonies
https://images.app.goo.gl/uhggw7ja3PLrS2wE6
Biochemical tests?
oxidase +ve
Catalase +ve
What do we use for demonstration of growth factor requirements?
X- and V-factor requirement
Satellitism (grows on BA with presence of S.aureus)
review page 775 slides
Treatment and prevention?
Ampicillin
Cephalosporins
prevention-Hib conjugate vaccine in use
Info on H.aegyptius
strain of NTHi
targets conjuctiva
Brazillian Purpuric Fever
Characteristics of Brazillian Purpuric Fever?
Hemorrhagic mucosal lesions
fever
vomitting
septic shock
Info on H.ducreyi?
causes sexually transmitted ulcer
clinicals:
Painful shallow ulcers with granulomatous bases and purulent exudates
HACEK
Haemophilus spp. H.parainfluenzae
Aggregatibacter spp. (formerly Actinobacillus) ¢ A.actinomycetemcomitans ¢ A.segnis ¢ A.aphrophilus ¢
Cardiobacterium spp. ¢ C.hominis ¢ C.valvarum ¢
Eikenella corrodens ¢
Kingella spp. « K.kingae
Info on HACEK?
normal flore of oral cavity
can cause endocarditis
are opportunistic
