Characterization of intermediate phenotypes induced by chemically undefined laboratory media in virulent Bordetella bronchiseptica strains

The expression of many virulence factors of Bordetella bronchiseptica is re gulated by the bvgAS locus and reduced in response to environmental signals called modulators, Virulent strains can alternate between virulent (Bvg(+) ), intermediate (Bvg(i)), and modulated (Bvg(+)mod) phenotypes. Potential v accine antigens can be expressed by Bvgi strains grown only in the absence of modulators, In the present study we evaluated filamentous hemagglutinin (FHA) and outer membrane protein (OMP) expression in Bvg(+) B, bronchisepti ca strains grown in chemically undefined media: nutrient agar (NA), tryptic soy agar (TSA), tryptose phosphate broth (TPB), and brain-heart infusion ( BHI), Our results suggest that TSA and TPB usually induce semimodulation, s ince Bvg+ strains cultured in these media retained the expression of FHA an d virulence-associated OMPs in the 30 kDa region, but failed to express oth er virulence markers such as OMPs in the regions of 90 and 200 kDa, though they expressed flagellin (avirulence marker), On the other hand, NA and BHI usually induce modulation, Thus the assayed chemically undefined media sho uld not be used in vaccine production, Semimodulation induced by TSA and TP B can be accurately detected by SDS-PAGE Sarkosyl-insoluble OMP-enriched pr ofiles. The reduction or absence of OMPs in the regions of 90 and 200 kDa i s the most sensitive marker, and in some cases the presence of flagellin in intermediate profiles is another trait of the Bvg(i) phenotypes. Therefore these markers could be useful for selecting media for vaccine production. We also characterized the phenotype of Bvg(+) strains grown in Stainer-Scho lte broth, an expensive medium, with and without glutathione, and we have d etected no differences; this is the first attempt to reduce the cost of a B ordetella growth medium for veterinary vaccine production.