Microbiology & infectious diseases

• Gram negative coccobacilli, oxidase positive, facultative anaerobe
• Fastidious
  • Requires both X and V factors for growth (Baron: Medical Microbiology, 4th Edition, 1996)
• Opportunistic pathogen and normal oropharyngeal colonizer
  • Causes infection in neonates, immunocompromised persons and patients with chronic respiratory issues (Int J Infect Dis 2024;146:107120)
• 6 different serogroups (StatPearls: Haemophilus influenzae Infection [Accessed 20 August 2024])
  • Named A - F
    • Serogroup B (Hib) is common in invasive disease
  • Nontypeable (NTHi) strains lack capsule
• Community outbreaks and sporadic infections of invasive disease

Contributed by Megan Amerson-Brown, M.L.S., Ph.D. and Julia Hankins, Ph.D.

Contributed by Megan Amerson-Brown, M.L.S., Ph.D.

Contributed by Megan Amerson-Brown, M.L.S., Ph.D.

• Scand J Infect Dis 2007;39:521, Sci Rep 2022;12:15765, UpToDate: Epidemiology, Clinical Manifestations, Diagnosis, and Treatment of Haemophilus influenzae [Accessed 14 August 2024]

A 1 year old child presents to the emergency department with fever, lethargy and positive Kernig sign. A Gram stain of the cerebrospinal fluid (CSF) revealed Gram stain morphology as shown in the figure that only grew on chocolate agar. Which of the following is the most likely causative agent?

1. Escherichia coli
2. Haemophilus influenzae
3. Neisseria gonorrhoeae
4. Neisseria meningitidis

B. Haemophilus influenzae. H. influenzae is the only Gram negative coccobacillus organism listed. Answer A is incorrect because Escherichia coli has Gram negative rods. Answers C and D are incorrect because Neisseria meningitidis and N. gonorrhoeae are both Gram negative diplococci. In addition, E. coli, N. meningitidis and N. gonorrhoeae can all grow on blood agar.

Comment Here

Reference: Haemophilus influenzae

A 65 year old smoker presents to the emergency department with a persistent cough, purulent sputum and fever for > 1 week. Chest Xray reveals a right lower lobe consolidation. The microbiology laboratory reports abundant H. influenzae from the sputum culture. What does H. influenzae require for growth?

1. Hemin and NAD+
2. Only V factor
3. Only X factor
4. Red cells and NAD+

A. Hemin and NAD+. H. influenzae requires both the presence of hemin (X factor) and NAD+ (V factor) for growth. Answers B and C are incorrect because only 1 of the 2 necessary factors are listed. Answer D is incorrect because while red cells contain both hemin and NAD+, these nutrients are only available to the bacteria if the red cells are lysed.

Comment Here

Reference: Haemophilus influenzae

An unvaccinated 8 month old presents to urgent care with fever, otitis media, congestion and purulent nasal discharge. The Gram stain from the sinus wash shows 4+ Gram negative coccobacilli. The patient is discharged on amoxicillin clavulanate. 2 weeks later, the patient is admitted for symptoms of meningitis in which the cerebrospinal fluid grew H. influenzae. Which virulence factor of H. influenzae is primarily responsible for the invasive nature of this child’s disease?

1. Capsular polysaccharide
2. IgA protease
3. Lipopolysaccharide (LPS)
4. Pili

A. Capsular polysaccharide. The capsular polysaccharide prevents phagocytosis and allows the organism to cross the epithelial and endothelial barriers and become invasive. Cerebrospinal fluid infection is an invasive infection. Answer B is incorrect because IgA protease leaves IgA to allow for successful colonization. Answer C is incorrect because lipopolysaccharide triggers the inflammatory process. Answer D is incorrect because pili aids in attachment to mucosal epithelia.

Comment Here

Reference: Haemophilus influenzae