Haemophilus genus Flashcards
General features and habitat of Haemophilus Influenzae
Gram –
Coccobacillus
Habitat- can be part of the upper respiratory flora
Biochemical Properties of Haemophilus Influenzae
Polysaccharide Capsule (A-F)- most important is serotype B (= E. coli K100 antigen)
Fastidious- requires special factors
Pathogenesis of Haemophilus Influenzae
Transmitted by respiratory droplets (aerosol)- travel into the respiratory tract
Increased risk of infection in sickle cell and asplenic patients
Mainly in small children (<4y) and often associated with viral infection (e.g. influenza)
Clinical Features of Haemophilus Influenzae
Epiglottitis: (strains with type B capsule)
Cherry-red epiglottis
Drooling
Inspiration stridor
Can be accompanied with pneumonia (i.e. respiratory tract infection- RTI) and often with cellulitis (dermis and subcutaneous inflammation)
Meningitis- high mortality (strains with type B capsule)
Otitis media including sinusitis and milder upper RTI (non-capsulated strains)
Can also cause infect contact lens (conjunctivitis)
Diagnosis of Haemophilus Influenzae
Grows on Chocolate agar, only with added: (has characteristic “running-nose” smell)
Factor V: NAD (nicotinamide adenine dinucleotide)
Factor X: Hemin
“Satellite phenomenon”- grows in blood agar only near Staphylococci (i.e. S. aureus)
Antigen detection by latex agglutination and immunofluorescence (IF)
Serotyping- using capsule swelling (quelling) test
Treatment of Haemophilus Influenzae
Ceftriaxone against meningitis or system disease
Rifampin prophylaxis in close contacts
Ampicillin + Sulbactam = Unasyn (against beta-lactamase production)
Prevention of Haemophilus Influenzae
Hib vaccination- against type B capsule
Vaccination is made by polysaccharide conjugated to diphtheria toxoid,
administered between 2 to 18 months (2, 3, 4, 18 months)
Other haemophilus species
H. parainfluenzae H. haemolyticus H. parahemolyticus H. aegypticus H. ducreyi
H. parainfluenzae
Gram negative
coccobacillus
Similar diseases to H. influenzae
Diagnosis: chocolate agar with only V factor required
H. haemolyticus
Gram negative
coccobacillus
Diagnosis: has haemolysis activity
Diagnosis: chocolate agar with both factor V and factor X required
H. parahemolyticus
Gram negative, coccobacillus
Diagnosis: has haemolysis activity
Diagnosis: chocolate agar with only V factor requirement
H. aegypticus
Gram negative
elongated rod
Can cause- conjunctivitis and Brazilian Purpuric Fever (in children)
Diagnosis: chocolate agar with both factor V and factor X required
H. ducreyi
Gram negative
elongated rod
Transmitted by sexual contact (STD) Symptoms:
Ulcus molle (A.K.A chancroid or soft chancre)- painful, unlike syphilis
Regional lymphadenitis
Diagnosis: chocolate agar with only X factor requirement
Treatment: Erythromycin, Fluoroquinolone
Differential Diagnosis: between- Syphilis, Herpes Simplex Virus (HSV), LGV (Chlamydia)
