Relationship between the Bvg+ phenotype of clinical isolates of Bordetella bronchiseptica and their immunogenic potential

Bordetella bronchiseptica is an important etiological agent of respiratory infections in companion and livestock animals and is characterized by pronounced phenotypic plasticity regulated by the two-component BvgAS system. The stability of the Bvg + phase determines the level of expression of adhesive and toxigenic virulence factors; however, its applied signif i cance for the selection of production strains for inactivated vaccines remains insufficiently studied. The aim of the study was to determine the relationship between the stability of the Bvg + phenotype of clinical isolates of B. bronchiseptica , their adh e sion activity, dermonecrotic activity, ability to accumulate biomass, and induction of a specific humoral response. A co m prehensive phenotypic analysis of 25 clinical isolates was performed using the hemagglutination reaction, an adhesion assay with Vero cells, evaluation of dermonecrotic activity in vivo , and determination of biomass accumulation. According to the results, five isolates were classified as demonstrating a stable Bvg + phenotype. The immunogenic potential was assessed by the level of specific IgG after immunization with inactivated bacterial preparations (1 × 10 8 CFU/m L before inactivation). Isolates with a stable Bvg + phenotype were characterized by higher adhesion activity (2.6 ± 0.4 vs 1.4 ± 0.5 adhesion scores), dermonecrotic activity (8.2 ± 1.1 vs 3.9 ± 0.8 mm), and biomass accumulation (8.7 ± 0.3 vs 7.8 ± 0.5 log CFU/m L ). The level of specific IgG in the Bvg + group was significantly higher (0.88 ± 0.12 vs 0.54 ± 0.11 OD 450 ). A moderate positive correlation between dermonecrotic activity and IgG level was established (r = 0.61). ROC analysis demonstrated good pr e dictive ability of phenotypic markers (AUC = 0.84; 95% CI 0.70–0.98). The obtained results indicate that the stability of the Bvg + phenotype is associated with increased expression of virulence factors, a greater capacity for biomass accumulation, and a significantly higher induction of the humoral immune response. Phenotypic screening of Bvg + phase stability may be used as a tool for selecting promising production strains for the development of inactivated bacterial preparations.