Spontaneous phase variation in Bordetella pertussis is a multistep non-random process

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Pathogenic Bordetella pertussis strains can spontaneously lose virulence factors when cultured in vitro, a process known as phase variation.
• Understanding the mechanisms and patterns of this variation is crucial for vaccine development and understanding pertussis pathogenesis.

Purpose of the Study:

• To investigate the process of spontaneous phase variation in Bordetella pertussis.
• To determine the order of loss of key virulence factors during in vitro culturing.

Main Methods:

• Selection of spontaneous B. pertussis variants on selective solid media.
• Screening of variant strains for the presence of hemolysin, pertussis toxin, and filamentous hemagglutinin (FHA).
• Assessment of adenylate cyclase activity in relation to virulence traits.

Main Results:

• Variant strains showed differential loss of virulence factors, with 66% losing all traits.
• The order of virulence factor disappearance was hemolysin, then pertussis toxin, then FHA.
• Strains retaining virulence factors exhibited adenylate cyclase activity, and hemolysin loss quantitatively affected other traits.

Conclusions:

• Phase variation in B. pertussis is a non-random, multistep process.
• The sequential loss of virulence factors suggests a defined pathway for adaptation to in vitro conditions.
• Strain #18323 demonstrated stability of virulence factors, correlating with its unique growth capabilities.