Pasteurellaceae

• 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.

• 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

– It is characterized by pharyngitis, fever, and, difficulty breathing that progresses as swelling obstructs the airways. Be aware that non-type b encapsulated Haemophlius influenzae* infections may be on the rise.

• Conjunctivitis is more commonly associated with Gram-positive bacteria (specifically, Staphylococcus and Streptococcus).

• 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.

• Pasteurella multocida commonly colonizes the mouths of cats and dogs.
• Pasteurella canis colonizes the mouths of dogs.

– Pasteurella canis is less commonly associated with human infection.

• Coccobacilli
• Facultative anaerobes
• Polysaccharide capsules that comprise hyaluronic acid.
• Infection usually results from animal bites or scratches.

Pastuerella multocida

• Systemic infection particularly in individuals with immune or liver dysfunctions.
• Exacerbation of underlying chronic respiratory disease.

Pastuerella multocida and Pasteruella canis

• Localized cellulitis and lymphadenitis.

• Colonize the oropharynx of humans and animals; infections are relatively rare.

Actinobacillus equuli and Actinobacillus ligniereslii* can cause bite wound infections, especially bites by farm animals. Actinobacillus ureae* can cause septicemia, meningitis, and pneumonia. Actinobacillus hominis* can cause septicemia and pneumonia. This genus comprises species that were formerly classified as Actinobacillus or Haemophilus* – Be aware that some authors continue to refer to these species by their former genus names. Aggregatibacter actinomycetemcomitans is often found with Actinomyces* in mixed infections, hence its name. – Colonies are described as star-shaped or like cigars crossing. – It is associated with subacute endocarditis of damaged valves. – Some strains cause localized aggressive periodontitis; toxins, including leukotoxins, cause significant damage to the tissues of the oral cavity. Aggregatibacter aphrophilus* is also associated with endocarditis of damaged valves. – This bacteria has also been found in brain abscesses in children with congenital heart disease. Endocarditis caused by Aggregatibacter* species can be treated with cephalosporins

• Periodontitis treatment includes biofilm debridement and administration of doxycycline or other antibiotics.

Brain abscesses caused by Aggregatibacter aphrophilus* infection can be treated with meropenem.