Haemophilus influenzae

Haemophilus influenzae


Habitat

  • Mucous membrane of the upper respiratory tract of humans.
  • Found in the nasopharynx of approx. 75% of healthy peoples.

Morphology

  • Slender, short, gram-negative rods or coccobacillus
  • Non-Motile, No flagella or pilli
  • Capsules are present and important in pathogenicity.
  • Encapsulated form are coccobacilli.
  • Non-Capsulated are pleomorphic, long, thread, filamentous
  • Fastidious Microorganism
  • It is the first free-living organisms to have its entire genome sequenced; 1,830,140 bp of DNA and 1740 Genes.

Cultural characteristics

Culture

Characteristics

On Blood Agar

  • Translucent, low, convex or flat pinpoint colonies
  • Satellitism

On Chocolate Agar

  • Grayish, Transparent, smooth, low, convex or flat with a slightly splayed out, entire edge, mucoid, pale

Levinthal’s Broth or Filde’s Broth

  • Uniform Turbidi
  •  Facultative anaerobes and aerobic, grow also in 5% CO2.
  • Optimum Temperature: 35-37oC, Min: 20-25oC, Optimum pH: 7.6
  • Killed at 55oC for 30 minutes of heating
  • Fastidious,requires 2 accessory growth factors:
    • X-Factor
    • V-Factor

X-Factor(Hemin)

  • A head stable growth promoting substances present in Red Blood Cells 
  • Hemin, plays a role as an enzyme in respiration.

V-Factor(NAD)

  • A heat labile vitamin like substances.
  • V-Factor is involved in oxidation-reduction process in the growing bacterial cell.
  • Heating blood agar to about 75oC, until it acquires a chocolate agar, releases V-Factor from Red cells and also inactivates NADase activity.
  • Satellitism
    • On blood agar colonies of S Aureus release V-Factor during growth
    • Which defuses into the surrounding medium
    • Enhancing the growth of H. influenzae.
  • Influenzae requires pantothenic acid, thiamine and uracil.

Biochemical reaction

Test

Reaction

Catalase

+

Oxidase

+

Haemolysis

Fermentation:

Glucose 

 

+

Fructose

Galactose

+

Lactose

Mannose

Sucrose

Trehalose

Xylose

+

Antigenic Properties 

  • Capsular polysaccharide
    • Major antigenic determinant
    • based on which, it is typed into six capsular types a to f 
    • While noncapsulated strains are nontypable
    • Isolates from acute invasive infections belong to ‘b” mainly.
    • Type b capsule has unique structure containing pentose sugar (ribose and ribitol) in the form of Polyribosyl ribitol phosphate (PRP)
    •  Hib PRP is used in vaccine
  • Outer membrane protein (OMP)
  • Lipo-oligosaccharide
  • Serotyping of H. influenzae ie done by agglutination or quelling reaction 

Mechanism

Encapsulated organisms → penetrate the epithelium of the nasopharynx → invade the blood capillaries → infection. 

  • Capsule resists phagocytosis and complement-mediated lysis.
  • Maybe opportunistic
  • Transmitted by direct contact, inhalation of the respiratory tract droplets.

Pathogenicity

Haemophilus influenza b (Hib)

  • Major cause of childhood infectious disease.
  • Meningitis: 
    • M.C invasive disease of H influenza
    • children age 5 months to 5 years.
    • MC Complication of its meningitis – Subdural effusion
  • Primary bacteremia
  • Post-splenectomy infection(rare)
  • Pneumonia
  • Acute epiglottitis
  • Arthritis.
  • Acute bacterial rhinitis:
    • MC cause of bacterial rhinitis

Non-Capsulated influenzae (Nc-hi) 

  • Causes otitis media, conjunctivitis and sinusitis
  • Causes chronic bronchitis in adults

Diagnosis

  • Meningitis
    • CSF gram’s stain and culture on iso Vitale X-enriched chocolate agar
    • If culture negative – Detection of PRP
  • Respiratory tract infection
    • Suggested by the predominance of gram-negative coccobacilli among abundant polymorphonuclear leukocytes in sputum.

Treatment

  • DOC for H. influenzae meningitis is –> Third generation cephalosporin.
  • Ceftriaxone or cefotaxime
  • Also in other invasive infection

Vaccination

  • Hib conjugate vaccine
  • First dose: 2 months
  • Rest of primary series: 2-6 months
  • Booster Dose: 12-15 months

Exam Important

Habitat

  • Mucous membrane of the upper respiratory tract of humans.

Morphology

  • Slender, short, gram-negative rods or coccobacillus
  • Capsules are present and important in pathogenicity.

Cultural characteristics

  • Requires 2 accessory growth factors:
    • A head stable growth promoting substances present in Red Blood Cells (X-Factor) 
    • A heat labile vitamin like substances (V-Factor).

Antigenic Properties  

  • Major surface antigen
  1. Capsular polysaccharideOuter membrane protein (OMP)
    • Major antigenic determinant
    • Based on which, it is typed into six capsular types a to f 
    • While noncapsulated strains are nontypable
    • Isolates from acute invasive infections belong to ‘b” mainly.
  2. Lipo-oligosaccharide
  • Serotyping of H. influenzae ie done by agglutination or quelling reaction 

Pathogenicity

Haemophilus influenza b (Hib)

  • Major cause of childhood infectious disease.
  • Meningitis: Primary bacteremia
    • M.C invasive disease of H influenza
    • children age 5 months to 5 years.
    • MC Complication of its meningitis – Subdural effusion
  • Post-splenectomy infection(rare)
  • Pneumonia
  • Acute epiglottitis
  • Arthritis.
  • Acute bacterial rhinitis:
    • MC cause of bacterial rhinitis

Non-Capsulated influenzae (Nc-hi) 

  • Causes otitis media, conjunctivitis and sinusitis
  • Causes chronic bronchitis in adults

Treatment

  • DOC for H. influenzae meningitis Cs –> Third generation cephalosporin.
  • Ceftriaxone or cefotaxime

 

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