Pasteurellaceae Lecture 20 Flashcards
Pasteurellaceae
Haemophilis, aggregatibacter, actinobacillus, pasteurell
small gram negative rods, can be pleomorphic
facultative anaerobe
most require enriched media for isolation
of this family, haemophilus are most commonly isolated human pathogen
haemophilus
relatively few species pathogenic to humans
nearly all human disease due to strains of haemophilus influenzae
colonize the upper respiratory tract in the first few months of life
other significant species: H influenzae biogroup aegyptis infeciton results in acute purulent conjuctivitis. H aphophilus and parainfluenza associated with endocarditis and infections in aimmunocomrpomised hosts.
Haemophilus influenzae
Haemophilus means blood loving
indicates requirement for blood factors for growth.
Hemin or x factor:heat stable iron containing protoporphyrin essential for electron transport chain and important for aerobic growth
v factor (v for vitamin): coenzyme nicotinamide adenine dinucleotide NAD
both present in blood enriched media but must be gently heated to destroy the inhibitors of V facotr. use heated blood agar, “chocolate” agar for isolation
Haemophilus influenzae physical features and things
capsulated or unencapsulated. Capsulated is typable and unencapsulated are non typable
strains without polysaccharide capsules (non-typable) cause infections of mucosal surfaces. OM, sinusitis, bronchitis, and pneumonia. Rarely diseminate
capsular polysaccharides: encapsulated strains (typable) cause majority of invasive disease. Composed of polyribitol phosophate (PRP). can express one of six polysaccharide capsules (A, B, C, D, E, or F). Haemophilus inflenza type B (HiB) accounts for 95% of all strains taht cause invasvie disease.
Type B strains of H flu features
dd
Pathogenesis and immunity: mucosal colonization. H. Flu
transmission from carrier to new host.
colonization must overcome nonsepcific mucociliary defenses
outer membrane proteins (OMP) p2 and p5 promote bacterial binding to mucous
LPS damages ciliated cells
adhesins and pili mediate direct adherence to nonciliated epithelial cells
IgA proteases cleave IgA
invasion into cells and subepithelial space
biding and uptake of iron and heme allow organisms to persist
Pathogenesis and immunity: mucosal infections H. Flu
disease due to unencapsulated (non-typable strains)
direct movement of organisms: through nasal ostia to the sinuses
eustachian tubes to middle ear to cause otitis media
down bronchi to cause bronchitis and pneumonia
precipitating factors cigarette smoke, allergic disease, and viral infection
Pathogenesis and immunity: invasive disease H. Flu
mucosa to bloodstream to distal sites
caused by typable strains (most HiB)
invade mucosa by separating apical tight junctions of columnar epithelium and moving intercellularly
bacteremia initially low in concentration but increases in matter of hours
polysaccharide capsule is antiphagocytic and major virulence factor
Pathogenesis and immunity: invasive disease: H. Flu
severity of infection related to rate of clearance of bacter.ia. When bacterial Conc. > 10^4/ MI metastatic seeding occurs.
antibodies directed against the capsule stimulate phagocytosis and complement mediated activity. Antibodies formed following natural infection, vaccination, or passive maternal transfer.
risk of meningitis and epiglottitis increased in patients with no anti PRP antibodies, complement deficiency, or post splenectomy
Epidemiology H. Flu
humans are only natural host
most children colonized during the first 5 years of life
person to perosn transmission through respiratory droplets
bimodal seasonal pattern with peaks Sept-Dec and march -may
children between 6-18 months at highest risk of invasive disease
prior to vaccination estimated 20,000 cases of invasive HiB anually in children <5.
worldwide HiB remains major childhood pathogen with 3 million cases and 700,000 fatalities annually
Clinical syndromes: meningitis H.Flu
prior to routine vaccination was most common cause of pediatric meningitis
nonspecific signs and symptoms especially in younger children. 1-3 day history of mild upper respiratory disease. Irritability, fever, lethargy
older children may have headache, photophobia, and meningismus
fulminant disease: rapid neurological deterioration
Clinical syndromes: meningitis 2 H.Flu
complications include seizures, cerebral edema, empyema, SIADH and herniation
mortality rate approximately 5%
long term sequelae include hearing loss, development delay, and visual impairments.
Clinical syndromes: epiglottitis H.FLu
cellulitis and swelling of supraglottic tissues
can result in acute upper airway obstruction
peak incidence of disease in 2-4 years olds
rare in the post vaccine era
abrupt onset of high fever, sore throat, dysphagia and sepsis
airway managemnt crucial. Keep child calm. emergency nasotracheal intubation in OR (in case need of trach) by ENT or anesthesia
Clinical syndromes: cellulitis H.FLu
relatively uncommon form of HiB disease
in pre vaccine era seen mostly in children <2
most located in cheek, periorbital region, or neck
manifests as fever with unilateral raised warm and tender area. may progress to violaceous hue
secondary focus may be present in 10-15% of patient
Clinical syndromes: arthritis H. Flu
prevaccine leading cause of septic arthritis in children <2
most often affects single large joint
disease due to bacteremic spread
presents with fever, decreased range of motion, warmth and sweling
10-20% with contiguous osteomyelitis
requires surgical drainage and IV antibiotic therapy
can occur in older populations but usually immunocompromised.