Bactericidal substance produced by Haemophilus influenzae b.

Area of Science:

• Microbiology
• Bacteriology
• Molecular Biology

Background:

• Bacteriophage studies on Haemophilus influenzae have led to unexpected discoveries.
• Certain strains of H. influenzae produce substances with antimicrobial properties.

Purpose of the Study:

• To characterize a novel bactericidal substance released by Haemophilus influenzae strains.
• To determine the properties and spectrum of activity of this bactericidal factor.

Main Methods:

• Assaying bactericidal activity using plaque tests with an Rd strain indicator.
• Demonstrating activity in mixed broth cultures.
• Testing sensitivity to enzymatic treatments (trypsin, DNase, lipase, alpha-amylase), heat, and centrifugation.
• Evaluating dependence on divalent cations (Ca2+, Mg2+).

Main Results:

• A bactericidal substance active against multiple H. influenzae types, other Haemophilus species, and Enterobacteriaceae was identified.
• The factor is trypsin-sensitive but resistant to DNase, 2-mercaptoethanol, lipase, alpha-amylase, and heat (100°C for 20 min).
• Activity is independent of Ca2+/Mg2+ and the factor is not pelleted by high-speed centrifugation; it is not phage-like and does not exhibit 'single-hit' kinetics.

Conclusions:

• The identified bactericidal factor is a thermostable protein with a broad spectrum of activity.
• It is not a typical small molecular weight bacteriocin (colicin-like) due to its non-inducible nature and wider activity range.
• This protein represents a novel antimicrobial agent with potential therapeutic applications.