Studies on phase variation in Bordetella pertussis.

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Pathogenic Bordetella pertussis bacteria can spontaneously lose virulence factors when cultured in laboratory settings.
• This phenomenon, known as phase variation, results in non-pathogenic bacterial strains.
• Understanding the mechanisms of phase variation is crucial for studying B. pertussis virulence.

Purpose of the Study:

• To investigate the spontaneous phase variation process in pathogenic Bordetella pertussis strains.
• To determine the frequency and characteristics of variants exhibiting altered virulence traits.
• To elucidate the ordered loss of specific virulence factors during in vitro culturing.

Main Methods:

• Isolation and selection of spontaneous B. pertussis variants capable of growing on specific media.
• Screening of variant strains for the presence of key virulence-associated traits: hemolysin, pertussis toxin, and filamentous hemagglutinin (FHA).
• Assessment of adenylate cyclase activity in variants with retained virulence traits.

Main Results:

• In B. pertussis strains Tohama and 165, variants emerged at a frequency of 10^-6 to 10^-7.
• Variant strains showed distinct combinations of virulence factors, with 66% lacking all tested traits.
• The loss of virulence factors appeared ordered: hemolysin, followed by pertussis toxin, and finally FHA.
• Variants retaining at least one virulence trait also exhibited adenylate cyclase activity.

Conclusions:

• Bordetella pertussis phase variation is a non-random, ordered process involving the sequential disappearance of virulence factors.
• The observed stable variants represent the final outcome of phase variation, potentially reflecting changes in 'Phase I' colonies.
• Strain 18323 showed unique behavior, with variants retaining all virulence traits, correlating with its high intracerebral virulence.