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Haemophilus influenzae

Haemophilus influenzae. The genus haemophilus organisms are small gram negative cocco -bacilli (because rounded at ends). Long filamentous forms also seen. Some strains are capsulated. The commonest is Haemophilus influenzae . The other species of the genus haemophilus are.

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Haemophilus influenzae

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  1. Haemophilus influenzae

  2. The genus haemophilus organisms are small gram negative cocco-bacilli (because rounded at ends). • Long filamentous forms also seen. • Some strains are capsulated. • The commonest is Haemophilusinfluenzae. • The other species of the genus haemophilus are. 1. H. ducreyi 2. H. parainfleunziae 3. H. aegyptius

  3. Properties: • It is a gram negative rod ( coccobacillus). • A facultative anaerobe which grows best in media enriched with co2. • Temperature requirements 32-37 degree celcius • Has got a polysaccharide capsule. • Non capsulated forms also exist. • On the basis of type of capsule there are six serotypes numbered as a,b,c,d,e and f.

  4. Serotype b is most virulent type • Organism found only in humans.

  5. Pathogenecity: • Enters the body through respiratory tract • Two types of behaviours. 1. Asymptomatic colonization 2. Infections such as sinusitis, otitis media or pneumonia. • Organism produces IgA protease which neutralizes respiratory mucosal IgA. • This helps in its attachment to respiratory mucosa.

  6. After attachment to respiratory mucosa it can enter blood stream and cause. • Bacteremia and meningitis. • 95% of encapsulated forms (type b) responsible for these diseases. • Non capsulated forms are responsible for otitis media, sinusitis and pneumonia.

  7. In children the age group 6 months -6 years is most prone to infection by the organism. • Peak incidence is from 6 months- 1 year. • Virulence factors are polysaccharide capsule and endotoxin.

  8. Clinical features: 1.Meningitis is same in features to that caused by meningococcus and pneumococcus except that the onset of other symptoms along with drowsiness is rapid. 2.Otitis media and sinusitis cause pain in affected areas and redness and bulging of tympanic membrane.

  9. 3.Septic arthritis, cellulitis and sepsis (specially in splenectomized patients). 4.Rarely epiglotitis in young children. 5.Pneumonia in elderly specially those with chronic respiratory disease.

  10. Lab diagnosis: • Gram staining • Organism is grown on chocolate agar. • Chocolate agar is enriched with two factors. 1. Factor X (haematin) 2. Factor V (NAD). • Other species do not require both factors The colonies will be greyish-white, small and mucoid.

  11. Definitive diagnosis can be made with Quellung test • Additional means of identifying encapsulated strains include fluorescent-antibody staining of the organism and latex agglutination tests, which detect the capsular polysaccharide.

  12. Treatment: • Ceftriaxone is drug of choice in meningitis and other serious infections • Otitis media and sinusitis are treated with co-amoxiclav. • Prevention: • It is by vacination. • The vaccine given is called Hib • It is in conjugated form. Conjugated with a carrier protein.

  13. Given in between 2-15 months. • Conjugated is more effective than un conjugated one. • Rifampicin is given in close contacts

  14. Bordetella

  15. The genus Bordetella contains seven species. B. pertussis is by far the most important causative agent of whooping cough • Other important ones are B. parapertussis, B. bronchoseptica. • Properties: • B. pertussis is a tiny (0.5 to 1.0 m), gram-negative cocco-bacillary rod.

  16. Encapsulated • Obligate aerobe • The organism is also very susceptible to environmental changes and survives for little time outside the human respiratory tract. • Oxidase and Catalase positive. • The pilli of cell wail contain a protein called filamentous haemagglutinin(fha)

  17. Epidemiology: • B. pertussis is spread by droplets produced by patients in the early stages of illness. • It is highly contagious, infecting 80 to 100% of exposed susceptible persons. • Pathogenesis: • B. pertussis is a strict human pathogen • Primarily a disease of infants and children

  18. The organism attaches to the respiratory mucosa with the help of filamentous haemaglutinin (fha). • Once attached, the bacteria immobilize the cilia and begin a sequence in which the ciliated cells are progressively destroyed and extruded from the epithelial border

  19. B. pertussis does not directly invade the cells of the respiratory tract or spread to deeper tissue sites. • Including filamentous haemagglutinin it produces four virulence factors. 1.Pertussis toxin ( Exotoxin) is a single antigen causing local tissue damage associated with inflammation. • This exotoxin has a B subunit that binds to target cell receptors, "unlocks" the cell, allowing entry of the A subunit.

  20. The A subunit activates cell-membrane-bound G regulatory proteins,which in turn activate adenylate cyclase. This results in production and outpouring of cAMP, which activates protein kinase and other intracellular messengers. • It causes promotion of lymphocytosis and inhibition of phagocytosis.

  21. 2.Extra cytoplasmic adenylate cyclase: • The organisms also synthesize and export adenylate cyclase. This enzyme, when taken up by phagocytic cells can inhibit their bactericidal activity. 3)Tracheal cytotoxin: is a fragment of the bacterial peptidoglycan that damages ciliated cells of the respiratory tract.

  22. Tracheal cytotoxin appears to act along with endotoxin to induce nitric oxide, which kills the ciliated epithelial cells. • Clinical Findings: • Whooping cough is an acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by a severe paroxysmal cough, which lasts from 1 to 4 weeks.

  23. Occurs in three distinct stages: • Catarrhal stage: mild upper respiratory tract infection • Paroxysmal stage: extends to the lower respiratory tract, with severe cough • Convalescent stage: less severe cough that may persist for several months

  24. Lab diagnosis: • Gram staining. • The organism can be isolated from nasopharyngeal swabs taken during the paroxysmal stage. Bordet-Gengou medium or Regan-Lowe is used for the culture. • Direct fluorescent-antibody staining of the nasopharyngeal specimens is often used for diagnosis.

  25. Polymerase Chain Reaction • Treatment: • Erythromycin reduces the number of organisms in the throat and decreases the risk of secondary complications • Prevention: • By vaccination

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