Haemophilus Infections and Conjunctivitis

Haemophilus spp. and Other Fastidious Gram-Negative Bacilli

Satellitism

• Phenomenon where Haemophilus spp. require V factor
• Occurs when Staphylococcus aureus, Streptococcus pneumoniae, or Neisseria spp. produce V factor
• Organisms: source of V factor
• BAP: source of X factor

Pasteurellaceae Characteristics

• Genera: Haemophilus, Actinobacillus, Pasteurella, and Aggregatibacter
• Gram-negative, pleomorphic, coccoid to rod-shaped cells
• Generally bacilli
• Nonmotile and facultative anaerobic
• Catalase and nitrate to nitrite reduction (+)
• Oxidase negative (-)

HACEK

• Reside in human oral mucosa
• Causes endocarditis
• Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella

Haemophilus spp. Characteristics

• Derived from Greek word meaning "blood-lover"
• Require X factor (hemin or hematin) and V factor (nicotinamide adenine dinucleotide)
• BAP (Blood Agar Plate) for V factor dependent Haemophilus spp.

Adherence Mechanisms

• NTHi strains: adherent to human epithelial cells, localized infection
• Serotype B: not adherent to human epithelial cells, systemic infections

Infections

• Haemophilus aegyptius: acute conjunctivitis (Koch-Weeks bacillus), "pink eye"
• Haemophilus influenzae biogroup aegyptius: conjunctivitis in pediatric patients, nonencapsulated, causes systemic disease known as Brazillian purpuric fever (BPF)
• Haemophilus ducreyi: strict human pathogen, smallest pathogenic bacteria, causative agent of chancroid (highly communicable ST genital ulcer disease)
• Haemophilus parainfluenzae: endocarditis, mitral valve as primary site of infection

Laboratory Diagnosis

• Haemophilus ducreyi and Haemophilus aegyptius: CAP with 1% IsoVitaleX or Vitox (source of X and V factor)
• Haemophilus ducreyi: grows best at 33°C, Nairobi biplate, GC agar base with 2% bovine hemoglobin and 5% fetal calf serum with vancomycin, Mueller Hinton agar with 5% chocolatized horse blood with vancomycin

Macroscopic Examination

• Haemophilus influenzae: translucent, tannish, moist colonies with a distinct "mousy" or bleach-like odor
• Haemophilus parainfluenzae: tannish and drier with a medium to large size compared with Haemophilus influenzae
• Haemophilus haemolyticus and Haemophilus parahaemolyticus: β-hemolytic on BAP
• Haemophilus ducreyi: small, flat, smooth, nonmucoid, transparent to opaque colonies, "clumpy" nonhemogeneous appearance when suspended in saline

Microscopic Examination

• Small, gram-negative coccobacilli to long filaments
• Haemophilus ducreyi: pale staining gram-negative coccobacilli arranged singly or in groups, "school of fish" or "railroad tacks" or "fingerprints"

Biochemical Tests

• Porphyrin Test: alternative method for differentiating the hemeproducing species of Haemophilus
• Principle: based on the ability of the organism to convert the substrate δ-aminolevulinic acid (ALA) into porphyrins or porphobilinogen
• Reagent: p-dimethylaminobenzaldehyde (Kovacs' reagent)
• Result: red color in lower aqueous phase (presence of phosphobilinogen), reddish orange fluorescence in UVL detection at 360 nm (presence of porphyrins)

This quiz covers the basics of Haemophilus infections, including adherence mechanisms, types of infections, and specific strains such as NTHi and Haemophilus influenzae biogroup aegyptius. It also touches on conjunctivitis and its causes.