Haemophilus influenzae
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The genus haemophilus organisms are small
gram negative cocco-bacilli (because rounded
at ends).
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Long filamentous forms also seen.
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Some strains are capsulated.
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The commonest is Haemophilus influenzae.
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The other species of the genus haemophilus
are.
1. H. ducreyi
2. H. parainfleunziae 3. H. aegyptius
Properties:
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It is a gram negative rod ( coccobacillus).
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A facultative anaerobe which grows best in
media enriched with co2.
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Temperature requirements 32-37 degree
celcius
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Has got a polysaccharide capsule.
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Non capsulated forms also exist.
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On the basis of type of capsule there are six
serotypes numbered as a,b,c,d,e and f.
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Serotype b is most virulent type
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Organism found only in humans.
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Pathogenecity:
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Enters the body through respiratory tract
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Two types of behaviours.
1. Asymptomatic colonization
2. Infections such as sinusitis, otitis media
or pneumonia.
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Organism produces IgA protease which
neutralizes respiratory mucosal IgA.
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This helps in its attachment to
respiratory mucosa.
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After attachment to respiratory mucosa it
can enter blood stream and cause.
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Bacteremia and meningitis.
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95% of encapsulated forms
(type b) responsible for these diseases.
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Non capsulated forms are responsible for
otitis media, sinusitis and pneumonia.
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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.
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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.
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.
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Lab diagnosis:
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Gram staining
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Organism is grown on chocolate agar.
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Chocolate agar is enriched with two factors.
1. Factor X (haematin)
2. Factor V (NAD).
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Other species do not require both factors
The colonies will be greyish-white, small and
mucoid.
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Definitive diagnosis can be made with Quellung
test
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Additional means of identifying encapsulated
strains include fluorescent-antibody staining of
the organism and latex agglutination tests,
which detect the capsular polysaccharide.
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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.
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Given in between 2-15 months.
Conjugated is more effective than un
conjugated one.
Rifampicin is given in close contacts
Bordetella
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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.
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Encapsulated
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Obligate aerobe
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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)
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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
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The organism attaches to the respiratory
mucosa with the help of filamentous
haemaglutinin (fha).
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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
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.
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The A subunit activates cell-membranebound 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.
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It causes promotion of lymphocytosis and
inhibition of phagocytosis.
2.Extra cytoplasmic adenylate cyclase:
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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.
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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.
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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
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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.
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Polymerase Chain Reaction
Treatment:
Erythromycin reduces the number of
organisms in the throat and decreases
the risk of secondary complications
Prevention:
By vaccination