Haemophilus
Microbiology:
Pleiomorphic small rods or coccobacilli
Facultative anaerobes
Growth of most species requires addition of X factor and/or V factor on chocolate agar.
Pili and non-pilus adhesins that attach to host cells are key to pathogenesis.
Haemophilus influenzae
This species derives its name from early suspicions that it was the causative agent of influenza, which we now know is caused by a virus.
Microbiology:
Spread in air droplets and respiratory secretions.
Endotoxin comprises lipo-oligosaccharide, which impairs ciliary function and damages respiratory epithelium.
Allows the bacteria to evade ciliary clearance and to invade pharyngeal tissues to reach the blood.
IgA 1 protease inhibits humoral immunity, which would otherwise activate complement and destroy the microbes.
Pili are specifically adapted to adhere to mucus, epithelial cells, and extracellular matrix proteins.
Haeomophilus influenzae Non-Encapsulated
Aka, Non-typeable
Common colonizers of the upper respiratory tract
Opportunistic pathogens that invade epithelial cells and macrophages, which facilitates infection.
Associated with sinusitis, otitis, bronchitis, and pneumonia.
These infections are more likely in individuals with adaptive immune system deficiencies; in healthy individuals, serum is bactericidal and prevents microbial spread.
Haemophilus influenzae Encapsulated
Further classified into serotypes a – f based on the antigens of their polysaccharide capsules
These strains are more often associated with invasive disease.
Prior to the development of an effective vaccine, Haemophilus influenzae type b was a significant cause of pediatric bacterial infections; in regions where immunization programs are not well-established, it remains a major source of childhood illness.
Meningitis particularly in children 3-18 months of age
Arthritis
Cellulitis around the cheeks and periorbital area.
Epiglottitis is a life-threatening disease that primarily affects children 2-4 years old
Characterized by pharyngitis, fever, and, difficulty breathing that progresses as swelling obstructs the airways.
Haemophilus aegyptius
Occasionally causes acute purulent conjunctivitis.
Conjunctivitis is more commonly associated with Gram-positive bacteria (specifically, Staphylococcus and Streptococcus).
Be aware that some authors call Haemophilus aegyptius a biogroup of Haemophilus influenzae.
Haemophilus ducreyi
Causes chancroid, a sexually transmitted infection that is uncommon in the United States.
Be aware that some authors call Haemophilus aegyptius a biogroup of Haemophilus influenzae.
Infection causes genital ulcers that can be treated with erythromycin.