The Journal of Medical Microbiology, Vol 30, Issue 3 213-217, Copyright © 1989 by Society for General Microbiology
The influence of cultural conditions on the expression in Salmonella typhimurium of an antigen related to cholera toxin
G. M. Qi, G. J. Clarke, T. S. Wallis and J. Stephen
Department of Microbiology, University of Birmingham.
The choice of strain, culture conditions, composition of medium and size of
inoculum all affected the expression of a cholera-toxin-related antigen
(CTRA) in Salmonella typhimurium. A previous study had shown that the
number of organisms expressing CTRA in Casamino acid Yeast Extract (CYE)
medium decreased between 4 h and 6 h in uninterrupted culture. In the
present experiments, organisms harvested at 4-5 h were subcultured into
fresh CYE medium and incubated for a further 2 h; the total number of
organisms increased, and the decrease in the proportion of organisms
expressing CTRA was reduced. Use of Hartley Digest Broth in place of CYE
medium increased the proportion of organisms expressing CTRA in all strains
tested, in both the uninterrupted and the subculture procedures. The higher
the initial inoculum, the lower was the proportion of organisms expressing
CTRA. The presence of the antigen in cells remained constant for about 18 h
after transfer from 37 degrees C to 4 degrees C. These data have important
implications for the production and purification of CTRA: they show that it
was expressed during log-phase of growth, and they suggest that expression
was regulated by a non-growth-limiting factor. Moreover, some avirulent
strains were better producers of the antigen than virulent ones. The
significance of the data is discussed in relation to the in-vivo situation.
