Sl. Walker et al., THE EFFECTS OF GROWTH DYNAMICS UPON PH GRADIENT FORMATION WITHIN AND AROUND SUBSURFACE COLONIES OF SALMONELLA-TYPHIMURIUM, Journal of applied microbiology, 82(5), 1997, pp. 610-614
pH measurements made in and around submerged colonies of Salmonella ty
phimurium grown within a model gelatin gel system using pH-sensitive m
icro- and macroelectrodes indicated some pH heterogeneity occurring in
and around the bacterial colony. Inoculation density, initial pH and
glucose concentration were all found to influence colony diameter and
metabolism of Salmonella colonies. Colony growth in the presence of gl
ucose, at pH 7.0 with an inoculation density of 1 cell ml(-1) led to a
pH fall of 1-2 pH units after 2 d. At pH 5.0, with glucose, colony gr
owth rates were much slower than at pH 7.0, and the pH change varied b
y less than one pH unit often becoming alkaline. In the absence of glu
cose, only small pH changes were observed within the medium, although
growth rates were similar to those in glucose-containing media. At the
higher inoculation density (ca 1000 cells ml(-1)), isolated pH change
s were not observed. Morphological changes, such as the production of
annular rings, were noted in stationary phase colonies as was alkali p
roduction in colonies. These results are discussed in relation to obse
rvations with surface colonies.