Article available in PDF
- Haemophilus influenzae is found along the bacteria lineage: kindgom name:Bacteria,
- phylum name:Proteobacteria,
- class name:Gamma Proteobacteria;
- order:Pasteurellales,
- family name:Pasteurellaceae;
- genus name Haemophilus.
- The specie name is haemophilus influenzae
Haemophilus influenzae has other names by which it can be identifed as it was formely known as the Pfeiffer's bacillus or Bacillus influenzae. it is also known as haemophilus meningitidis,Mycobacterium influenzae,Influenza-bacillus to name a few.
other species that fall under the same genus name are: haemophilus ducreyi and haemophilus influenzae aegyptius
Characteristics
- It's Slender, short, gram negative rods or coccobacillus
- Measures 3-0.5 um X 0.5-1 um with rounded ends.
- Prolonged counterstaining for 5-15 minutes with very dilute carbol fuschin often gives satisfactory results.
- It is Non-Motile, No flagella or pilli
- It has Capsules which is important in pathogenicity.
- Encapsulated form are coccobacilli, CSF Sample while Non-Capsulated are pleomorphic, long, thread, filamentous
- It is Fastidious Microorganism require enriched media for growth.
- This is a group of small gram-negative, non-spore forming,
- Growth is enhanced in CO2 enriched atmosphere.
- Present in upper respiratory tract as a normal microbial flora
- in healthy people.
These are Fastidious microorganism requiring specific nutrient to be culture.These nutrients are Factor X (Hematin) and V (Diphosphopyridine nucleotide).
X-Factor (Hemin)
- Hemin, plays a role as an enzyme in respiration.
- Use human transferrin as a sole source of iron
- Provide protophyrin IX, iron can be obtained from another source
V-Factor (NAD)
- Present in the tissue of plants and animals.
- Heating blood agar to about 75˚C, until it acquires a chocolate agar, releases V-Factor from Red cells and also inactivates NADase activity.
- aureus release V-Factor during growth, which defuses into the surrounding medium, enhancing the growth of H. influenzae.
- influenzae will show Satellitism.
- V-Factor is involved in oxidation-reduction process in the growing bacterial cell.
- influenzae requires pantothenic acid, thiamine and uracil.
Growth factor required Haemophilus species
- X and V factor : H. influenzae, H. aegyptius, H. hemolyticus
- X factor : H. ducreyii
- V factor : H. parainfluenzae, H. parahemolyticus
Habitat
- It is found in the Mucous membrane of the upper respiratory tract of humans.
- Also Found in the nasopharynx of approx. 75% of healthy peoples.
The main species of medical importance are:
- H. influenzae
- H. ducreyii
- H. aegyptius
H. ducreyii
- Slender, gram-negative, ovoid bacilli, slightly larger than H.influenzae.
- Bacteria enmass have configuration of ‘shoals of fish”.
- It causes chancroid (tender genital ulcer).
- Cultured in special enriched media (20-30% rabbit blood agar) with colonic morphology of small grey glistening colonies surrounded by zone of hemolysis.
- It is treated by erythromycin, cotrimoxazole and third generation cephalosporins.
H. aegyptius
- It causes contagious conjunctivitis.
Haemophilus influenzae
Characteristics:
- Gram-negative cocobacilli.
- Fastidious bacteria requiring growth factors for isolation.
- Found in upper respiratory tract as normal flora in healthy people
Antigenic structure
- Capsular polysaccharide,There are six serotypes of H. influenzae, A-F.
. Capsular antigen type b is composed of
polyribose ribitol phosphate. H. influenzae type b is the most common cause of disease in humans.It is the main virulence factor which provides anti-phagocytic property.
- Outer membrane protein
- Lipo-oligosaccharide
Clinical features:
The bacteria causes disease most commonly in young children.
- Acute pyogenic meningitis
- Acute epiglottis
- Pneumonia
- Otitis media
- Siusitis
- Cellulitis
- Acute pyogenic arthritis
Mechanism
- Encapsulated organisms –> penetrate the epithelium of the nasopharynx –> invade the blood capillaries –> infection.
- Capsule resists phagocytosis and complement mediated lysis.
- May be opportunistic
- Transmitted by direct contact, inhalation of the respiratory tract droplets.
Laboratory diagnosis:
Specimen: Cerebrospinal fluid, sputum, blood, pus
Smear: Gram-negative short rods.
Culture:
Chocolate agar contain both X and V factor; blood agar contain only X factor.
On Blood Agar: translucent, low, convex or flat pin point colonies, Satellitism.
On Chocolate Agar: Grayish, Transparent, smooth, low, convex or flat with a slightly splayed out, entire edge, mucoid, pale.
Satellitism test is used to identify H. influenzae in blood agar.
Methods:
- Mix a loopful of haemophilus growth in 2ml of sterile saline.
- Inoculate the bacteria suspension on a plate of blood agar using a sterile swab.
- Streak a pure culture of S. aureus across the inoculated plate which provides V-factor for H. influenzae.
- incubate the plate over night in a CO2 -enriched environment at 35-37 Oc.
- Look for growth and satellite colonies in next morning.
NB: Colonies are largest nearest to the S. aureus column of growth.
Serology: Quellung reaction (using specific antisera)
Immunofluorescence stain
Biochemical Tests
| Test | Reaction |
| Catalase | + |
| Oxidase | + |
| Indole | +/- |
| Urease | +/- |
| Haemolysis | – |
| Fermentation | Reaction |
| Glucose | + |
| Fructose | – |
| Galactose | + |
| Lactose | – |
| Mannose | – |
| Sucrose | – |
| Trehalose | – |
| Xylose | + |
Treatment:
- Ampicillin
- Chloramphenicol
- Cotrimoxazole
- Third generation cephalosporins
Article available in PDF