Aim: To study pathogenic characteristics of B. pertussis strains isolated from patients during different periods of pertussis infection epidemic process.
Materials and methods: Strains of B. pertussis isolated in Moscow during 1967 - 1971, 1980 - 1985, and 2001 - 2005 were studied. Nutrient media: Bordet-Gengou blood agar, casein-charcoal agar.
Animals: mice - F1 hybrids (CBA x C57BL6). Pathogenic characteristics of strains were studied by assessment of virulence (LD50), leukocytosis-stimulating (LS units) and histamine-sensitizing (HSD50) activities of cultures. Genotyping was performed using standard equipment and reagents for DNA isolation, amplification, sequencing and detection of results.
Results: On the sample of 164 strains, pathogenic and genotypic characteristics of B. pertussis populations circulated during 1967 - 1971, 1980 - 1985, and 2001 - 2005. Majority of B. pertussis strains isolated in 1967 - 1971 and strains circulated during current phase of epidemic process were virulent (80.75% and 81.8% respectively) and had significant leukocytosis-stimulating and histamine-sensitizing activity, whereas strains isolated from patients with pertussis in 1980 - 1985 characterized by lower virulence and toxicity. Genotyping showed strains carrying "non-vaccine" allele ptxA1, which emerged in the middle of 1970s, totally displaced strains with "vaccine" alleles ptxA2 and ptxA4.
Conclusion: Adaptive changes of B. pertussis driven by increased vaccination coverage involve both ptxA gene and pathogenic characteristics of infectious agent in the range of genotypically homogenous population with domination of strains, which have high levels of virulence and toxicity.