3.2. Effect of magnesium addition on Salmonella spp. growth with TV
BPW + V medium containing TV was supplemented with increasing concentration of MgCl2 (1–15 g/l) and inoculated with low levels of Salmonella. Increase of Salmonella signals (growth and TV reduction) was observed (data not shown) with increasing magnesium concentration, maximizing at 5 g/l. Higher concentrations led to decrease in signals which was not due to pH variation but may result from osmotic stress on the bacterial structure.
Fig. 3 illustrates the impact of addition of 5 g/l of Mg2+ to the medium inoculated with Salmonella serotype Enteritidis, containing a high concentration of TV (1 g/l). Addition of Mg2+ in the culture medium led to an improvement of apparent growth rate and to a reduction of apparent lag. We also observed an important increase of the final optical density signal with magnesium addition. All these results seem to validate hypothesis of the protective effect of magnesium on the bacterial growth. Indeed, apparent growth rate improvement, reducing lag and final OD increase translate into better bacterial growth and formazan production.