Transcript Pasteurellaceae Pasteurellaceae  Classification – includes three medically important genera     Haemophilus Pasteurella Actinobacillus (we won’t be discussing this rare clinical isolate) Haemophilus species – these are fastidious “blood loving”

Pasteurellaceae
Pasteurellaceae
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Classification – includes three medically
important genera
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Haemophilus
Pasteurella
Actinobacillus (we won’t be discussing this rare
clinical isolate)
Haemophilus species – these are fastidious
“blood loving” organisms that require one or
both of two factors present in blood:
Haemophilus
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X=hemin - is necessary for the synthesis of iron
containing respiratory enzymes such as
cytochrome, cytochrome oxidase, catalase, and
peroxidase.
V=NAD - is a coenzyme required for oxidationreduction reactions
X is heat stable while V is heat labile
Morphology and cultural characteristics
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G-coccobacilli to g- filamentous rods (seen on Gram stains
of rough colonies)
Optimal growth is at 35-370 C, with an atmosphere of 510% CO2.
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H. ducreyi grows best at 33-350 C
Microscopic appearance of
Haemophilus
Gram stain of Haemophilus
Haemophilus
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With the exceptions of H. ducreyi (requires 4 days) and H.
aegyptius (requires 2-3 days), most grow in 18-24 hours.
On conventional sheep blood agar, X factor diffuses from
the RBCs into the medium, but the small amount of V
factor that diffuses out is destroyed by the NADase activity
that is present in the blood agar.
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Therefore, most will grow poorly or not at all on CBA plates.
Many will produce small colonies on CBA plates
surrounding colonies of Staph. aureus or Pseudomonas
which produce and secrete large amounts of NAD into the
medium.
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This phenomena is known as satelliting.
Satelliting
Haemophilus
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Haemophilus sp. grow best on chocolate agar.
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Heating (800 C for 15 min.) destroys the NADase activity
and releases the NAD from the RBCs.
Why would heating for too long be detrimental for the growth
of some Haemophilus sp.?
If a specimen is likely to be contaminated with large
amounts of NF, chocolate agar can be made selective for
H. influenzae by adding bacitracin, vancomycin, and
clindamycin.
Colonies on chocolate agar are grayish.
The hemolytic species are beta hemolytic
Colonies with capsules are smooth and non-encapsulated
organisms produce rough colonies
Haemophilus influenzae on Choc agar
Haemophilus
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The organisms are very susceptible to drying and chilling
(are autolytic) so specimens should not be refrigerated
and they should be processed quickly to avoid killing the
organisms
There are 10 different species that may be found in clinical
specimens: Influenzae, parainfluenzae, haemolyticus,
parahaemolyticus, aphrophilus, paraphrophilus,
paraphrohaemolyticus, aegyptius, ducreyi, and segnis
Biochemistry
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Are all oxidase +
Haemophilus
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Are speciated on the basis of hemolysis and X
and V factor requirements.
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Fermentation and catalase production are also used.
Which species require both X and V, and which
require only V?
H. ducreyi is the only species that requires only X,
though H. aphrophilus may require it on initial isolation
V factor requirement
X factor requirement
X and V factor requirements
Speciation of Haemophilus
Haemophilus
H. influenzae can be differentiated from H.
aegyptius by its fermentation of xylose (H.
aegyptius is -)
 H. influenzae is further subdivided into 7
biotypes, with type I being associated with more
invasive disease.
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Immunoserologic ID
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H. influenzae is divided into 6 serotypes based
on capsular polysaccharide.
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Type b is the most virulent.
Haemophilus
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Mechanisms of pathogenicity
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Capsule – the type b serotype, in particular, is poorly
immunogenic and antiphagocytic
Adhesions – both pili and outer membrane proteins may
act as adhesions
IgA protease
Endotoxin
Clinical significance – H. influenzae
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Nonencapsulated H. influenzae is part of the NF of the
nasopharynx in 75% of children and a lower % of adults.
H. influenzae type b (Hib) is a major pathogen, particularly
in children where the initial focus of infection is the
nasopharynx followed by invasion of local tissue and
sometimes the bloodstream.
Haemophilus
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Meningitis – occurs in individuals between 2 months and
three years of age.
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Epiglottitis – occurs in 2-4 year olds with mostly boys
being affected.
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Before 2 months the infant is protected by residual
antibodies from mom and after 3 years active immunity has
occurred.
Following infection, long term sequelae such as deafness,
speech impairment, and behavior abnormalities may occur.
Starts as a sore throat and progresses to cough and fever
and then to respiratory distress with blockage of the air
passage and death from suffocation.
Pneumonia - frequently associated with otitis media,
meningitis, and septicemia
Haemophilus
Septic arthritis, cellulitis, and pericarditis in
children under 2 years of age
 In adults and children, nonencapsulated
varieties may cause secondary infections of
acute sinusitis or bronchitis.
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Clinical significance-H. aegyptius (KochWeeks bacillus)
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Causes acute and contagious conjunctivitis
(commonly called pink eye)
Haemophilus
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Clinical significance-H. ducreyi
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Causes a venereal disease called chancroid or
soft chancre which is transmitted by direct
contact and is more commonly seen in hot,
tropical countries.
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After an incubation of 4-7 days, lesions appear on
genitals or adjacent areas.
The lesions are small, tender, and red, but they rapidly
become pustular, eroded, and ulcerated.
They may spread to neighboring lymphatics causing
buboes, but they do not spread further.
The chancre is autoinoculable, resulting in multiple
lesions.
Chancroid
Haemophilus
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Clinical significance – other species
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May be part of the NF of the oropharynx and may
occasionally cause endocarditis, meningitis, sinusitis, or
pneumonia.
Can cause invasive disease following a human bite.
Antimicrobial therapy and treatment
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Many strains of H. influenzae now produce beta lactamase
so testing is necessary.
Chloramphenicl or tetracycline are usually effective
There is a Hib vaccine given to infants
For chancroid - sxt or erythromycin is effective
Pasteurellaceae
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Pasteurella
Is a small Gram-negative bacillus
 Is fermentative, but anaerogenic, nonmotile, and oxidase +.
 P. multocida is the most commonly isolated
species.
 The organisms are usually associated with
animals other than man
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Pasteurella
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P. multocida won’t grow on a Mac plate and
may exhibit bipolar staining
Pasteurella
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TSI results may be confusing because of weak acid
production
Virulence factors
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Capsule
Endotoxin
Clinical significance
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P. multocida is NF in the respiratory tract of a wide variety
of organisms including dogs and cats.
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Clinical isolates in humans usually from a localized infection
produced after a dog or cat bite or scratch.
It may occasionally progress to osteomyelitis or arthritis.
Pasteurella
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Antimicrobial sensitivity
Is exquisitely sensitive to penicillin (Sensitivity to
2U of penicillin may be used for presumptive ID)
 Tetracycline and chloramphenicol may also be
used
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