Viable, but non-culturable, state of a green fluorescence protein-tagged environmental isolate of Salmonella typhi in groundwater and pond water

An environmental isolate of Salmonella typhi was chromosomally marked with a gfp gene encoding green fluorescence protein (GFP) isolated from Aequorea victoria. The hybrid transposon mini-Tn5 gfp was transconjugated from E coli to S typhi, resulting in constitutive GFP production. The survival of S typhi GFP155 introduced into groundwater and pond water microcosms was examined by GFP-based plate counts, total cell counts, and direct viable counts. A comparison between GFP-based direct viable counts and plate counts was a good method for verifying the viable, but non-culturable (VBNC), state of S typhi. The entry into a VBNC state of S typhi was shown in all microcosms. S. typhi survived longer in groundwater than in pond water as both a culturable and a VBNC state.