Culturability and viability techniques such as plate count on solid
agar (PC), Most Probable Number (MPN) and Direct Viable Count-Fluorescence in Situ Hybridation (DVC FISH) were used
to study the inactivation of Salmonella
typhimurium by photo-Fenton process at pH 5.5. In the presence of only
simulated solar irradiation (500 W·m-2), S. typhimurim showed that both
culturability measured by MPN and viability (measured by DVC FISH) underwent
just a slight decreasing of 2 and 1 log respectively after 240 min of light
exposition while culturability measured by PC did not show any change. Results
after 48 h of dark conditions did not reveal re-growth. However, when
experiment was carried out in the presence of 2 mg L-1 of Fe3+ and 20 mg L-1 of H2O2 and pH 5.5, culturability was strongly affected after 240 min of simulated
solar irradiation; nevertheless, viability was only slightly altered (~1 log).
During dark period of 48 h changes on culturability and viability were not
observed. On the other hand, it was also found that sugar metabolism was
affected rather the amino-acids in S.
typhimurium cells irradiated at different times upon photo-Fenton conditions.
These findings might suggest for the first time that photo-Fenton process at pH
5.5 could induce viable but nonculturable state (VBNC) on waterborne S. typhimurium and that probably sugar
metabolism damage could activate the VBNC state.