Correlation between growth rate and loss of histamine-sensitizing factor during antigenic modulation in Bordetella...

The pattern of loss of histamine-sensitizing factor (HSF) during antigenic modulation of Bordetella pertussis in Hornibrook medium was examined. The aim was to determine the possible underlying mechanism involved in modulation. Normal (X-mode) B. pertussis cells were grown in Hornibrook medium in which 0.5% (w/v) NaCl had been replaced with 0.5% (w/v) MgSO4. 7H2O (C-medium). At various time intervals during growth, the viable cell numbers and optical densities of both cultures in the X- and C-media were estimated. Whole cells were harvested from the cultures at the same time intervals and aliquots from the cultures were assayed for the levels of their histamine-sensitizing properties. Correlation of the increase in viable cell numbers with rate of loss of histamine-sensitizing activity in both the cells and whole cultures indicated that components responsible for the histamine-sensitizing activity were not synthesized during modulation. Moreover, the loss of HSF from B. pertussis cells was faster than can be explained by dilution of the original factor in the inoculum among progeny cells. Modulation may involve cessation of synthesis and selective degradation or denaturation of some envelope polypeptides immediately upon inoculation of normal X-mode B. pertussis cells into C-medium.