بسم الله الرحمن الرحيم
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بسم الله الرحمن الرحيم. Haemophilus influenzae. Diseases. Sinusitis, otitis media & pneumonia are common. Epiglottitis is uncommon. H. influenzae used to be a leading cause of meningitis , but vaccine has greatly reduced number of cases. Haemophilus influenzae. Characteristics.

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بسم الله الرحمن الرحيم

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بسم الله الرحمن الرحيم


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Haemophilusinfluenzae

Diseases

  • Sinusitis, otitis media & pneumonia are common.

  • Epiglottitis is uncommon.

  • H. influenzae used to be a leading cause of meningitis, but vaccine has greatly reduced number of cases.


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Haemophilusinfluenzae

Characteristics

  • Small gram-negative (coccobacillary) rods.

  • Requires factors X (hemin) & V (NAD) for growth.

  • Of six capsular polysaccharide types, type b causes 95% of invasive disease.

  • Type b capsule is polyribitol phosphate.

Habitat and Transmission

  • Habitat is the upper respiratory tract.

  • Transmission is via respiratory droplets.


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Haemophilusinfluenzae

Pathogenesis

  • Polysaccharide capsule is the most important determinant of virulence.

  • Unencapsulated ("untypeable") strains cause mucosal infections but not invasive infections.

  • IgA protease is produced.

  • Most cases of meningitis occur in children younger than 2 years of age, because maternal antibody has waned & immune response of child to capsular polysaccharides can be inadequate.


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Haemophilusinfluenzae

Laboratory Diagnosis

  • Gram-stained smear plus culture on chocolate agar.

  • Growth requires both factors X & V.

  • Determine serotype by using antiserum in various tests, e.g., latex agglutination.

  • Capsular antigen can be detected in serum or cerebrospinal fluid.


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Haemophilusinfluenzae

Treatment

  • Ceftriaxone is the treatment of choice for meningitis.

  • Approximately 25% of strains produce β  -lactamase.

Prevention

  • Vaccine containing type b capsular polysaccharide conjugated to diphtheria toxoid or other protein is given between 2 & 18 months of age.

  • Rifampin can prevent meningitis in close contacts.


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Bordetella pertussis

Diseases

Whooping cough (pertussis).

Characteristics

Small gram-negative rods.

Habitat and Transmission

  • Habitat is the human respiratory tract.

  • Transmission is via respiratory droplets.


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Bordetella pertussis

Pathogenesis

  • Pertussis toxinstimulates adenylate cyclase by adding ADP-ribose onto inhibitory G protein.

  • Toxin has two components:

  • - Subunit A: has ADP-ribosylating activity

  • - Subunit B:binds toxin to cell surface receptors.

  • Pertussis toxin causes lymphocytosis in blood by inhibiting chemokine receptors prevents lymphocytes from entering tissue, resulting in large numbers being retained in blood.


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Bordetella pertussis

Pathogenesis

  • Inhibition of chemokine receptors occurs because pertussis toxin ADP-ribosylates inhibitory G protein prevents signal transduction within cell

  • Extracellular adenylate cyclase is produced

  • inhibit killing by phagocytes.

  • Tracheal cytotoxin damages ciliated epithelium of respiratory tract.


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Bordetella pertussis

  • Whooping cough is acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by severe paroxysmal cough, which lasts from 1 to 4 weeks.

  • Paroxysmal pattern is characterized by series of hacking coughs, accompanied by production of copious amounts of mucus, that end with inspiratory "whoop" as air rushes past narrowed glottis.

  • In adults, B. pertussis infection often manifests as paroxysmal cough of varying severity lasting weeks. The characteristic whoop is often absent. Adults with a cough lasting several weeks (often called the 100-day cough) should be evaluated for infection with B. pertussis.


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Bordetella pertussis

Laboratory Diagnosis

  • Gram-stained smear plus culture on Bordet-Gengou agar.

  • Identified by biochemical reactions & slide agglutination with known antisera.

  • PCR tests are both sensitive & specific.

Colonies of Bordetella pertussis growing on Bordet-Gengou agarThis fastidious bacterium grows as small colonies with a pearl-like sheen on this medium.


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Bordetella pertussis

Treatment

Erythromycin.

Prevention

  • Acellular vaccine containing pertussis toxoid & four purified proteins (recommended).

  • Killed vaccine: contains whole organisms.

  • Given to children in combination with diphtheria & tetanus toxoids (DTaP).


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Legionella pneumophila

Diseases

Legionnaires' disease ("atypical" pneumonia).

  • Clinical picture vary from mild influenzalike illness to severe pneumonia accompanied by mental confusion, nonbloody diarrhea, proteinuria & microscopic hematuria.

  • Cough with scanty & nonpurulent sputum.

  • Most cases resolve spontaneously in 7 to 10 days, but in older or immunocompromised patients, infection can be fatal.

  • Pontiac fever is mild, flulike form of Legionella infection that does not result in pneumonia.


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Legionella pneumophila

Characteristics

  • Gram-negative rods (stain poorly with standard Gram stain)

  • Require iron & cysteine for growth in culture.

Habitat and Transmission

  • Habitat is environmental water sources.

  • Transmission is via aerosol from the water source.

  • Person-to-person transmission does not occur.


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Legionella pneumophila

Pathogenesis

  • It has endotoxin.

  • Predisposing factors include:

  • - Older than 55 years of age

  • - Smoking damages alveolar macrophages

  • - High alcohol intake.

  • -Immunosuppressed patients (renal transplant recipients)

  • Organism replicates intracellularly, so cell-mediated immunity is important host defense.


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Legionella pneumophila


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Legionella pneumophila

Laboratory Diagnosis

  • Microscopy with silver impregnation stain or fluorescent antibody.

  • Culture on charcoal yeast extract agar containing increased amounts of iron & cysteine.

  • Urinary antigen provides rapid diagnosis.

  • Serologically by detecting rise in antibody titer in patient's serum.

  • Hyponatremia (serum sodium ≤ 130 mEq/L) is important laboratory finding that occurs more often in Legionella pneumonia than in pneumonia caused by other bacteria.


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Legionella pneumophila

H & E stained lung sections of patient from whom legionella pneumophila was isolated stained with CDC's modification of Dieterle silver impregnation procedure. small, blunt pleomorphic intracellular & extracellular bacilli which stain brown to black against a pale yellow background (500X)

Legionella pneumophila growing on GVPC agar

Charcoal yeast extract agar


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Legionella pneumophila

Treatment

  • Azithromycin or erythromycin.

  • Rifampin can be added in severe cases.

Prevention

No vaccine or prophylactic drug is available.


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