Phenotypic variation and modulation in Bordetella bronchiseptica

Most of the isolates of Bordetella bronchiseptica obtained by this laboratory possessed a characteristic colonial morphology when grown on Bordet- Gengou agar (BGA) at 37 degrees C. The colonies appeared domed (Dom+) with a smooth colonial surface (Scs+) and a clear zone of hemolysis ( Hly +). From these Dom+ Scs+ Hly + BGA colony types arose flat (Dom-), smooth colonial surface (Scs+) and nonhemolytic ( Hly -) variants at frequencies of 10(-2) to 10(-3). Isogenic pairs of Dom+ Scs+ Hly + and Dom- Scs+ Hly - BGA phenotype variants (BGA-PVs) were picked from 11 strains of B. bronchiseptica, and their whole cell lysates were compared with each other by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Characteristic SDS-PAGE profiles were observed for each of the Dom+ Scs+ Hly + and Dom- Scs+ Hly - BGA-PVs with regard to (i) surface-exposed proteins, based on autoradiographs of 125I- Iodogen -labeled organisms, (ii) polypeptide differences, based on gels stained with Coomassie brilliant blue R-250, and (iii) lipopolysaccharide differences based on gels stained with silver after oxidation with periodic acid. SDS-PAGE profiles were then used to monitor the phenotypes expressed by Dom+ Scs+ Hly + and Dom- Scs+ Hly - BGA-PVs transferred and grown on brucella agar, Trypticase soy agar, and nutrient agar. When grown on non-BGA media, the Dom+ Scs+ Hly + BGA-PVs from six of eight strains showed SDS-PAGE profiles identical to those of Dom- Scs+ Hly - BGA-PVs. This phenotypic change was reversible even after 15 subcultures on the non-BGA media, since Dom+ Scs+ Hly + organisms passed back onto BGA expressed both Dom+ Scs+ Hly + colonial morphology and Dom+ Scs+ Hly + SDS-PAGE profiles. The influence of cultural conditions on maintenance of virulence is discussed.