Phenotype evaluation of Bordetella bronchiseptica cultures by urease activity and Congo red affinity

Aims: The present study shows that Congo red binding and urease activity as says are useful for selection of virulent (Bvg(+)) Bordetella bronchiseptic a cultures. Methods and Results: Congo red binding and urease activity of Bvg(+) B. bro nchiseptica cultures in different liquid media were compared with the expre ssion of virulence markers such as filamentous haemagglutinin and some oute r membrane proteins (OMP). The correlation with the reference virulence mar kers allowed the establishment of cut-off values for the proposed markers t o assure the virulent phenotype (greater than or equal to 26 nmol ml(-1) of CR and less than or equal to2.6 U). Using both assays, modulated cultures with avirulent phenotype (Stainer-Scholte broth, with MgSO4 20 mmol l(-1) a nd brain heart infusion broth) and semi-modulated cultures with intermediat e phenotypes (tryptose phosphate broth and 83% Stainer-Scholte with MgSO4 5 mmol l(-1) cultures) could be distinguished. Conclusions: CR binding assay and urease activity are specific and sensitiv e enough to detect intermediate phenotypes that could only be detected by s ubtle changes in OMP profiles. Significance and Impact of the Study: The production of effective veterinar y vaccines is hampered by reversible B. bronchiseptica antigenic modulation . The proposed assays are technically suitable for selection of virulent cu ltures to optimize vaccine production.