The propensity of Salmonella to persist in water environments under unfavourable conditions is of concern as these water environments serve as contamination reservoirs. The role of contaminated water in the transmission of Salmonella in developing countries is largely unknown. The fate and persistence of non-typhoidal Salmonella in water environments and the specific influence of the indigenous microbiota on the survival and growth of Salmonella is poorly understood. A tagged Salmonella strain distinguishable in vivo from a mixed bacterial community would greatly facilitate the study of Salmonella in water environments. The clinically relevant S. enterica subsp. enterica ser. Typhimurium isolate was chromosomally tagged using the pUT mini–Tn5 Km transposon with the green fluorescent protein gene gfpmut3b*. Southern Blot hybridisation confirmed that the gfp gene had integrated into the chromosome. The gfp gene was stably maintained and the gfp-labelled recombinants were not growth rate impaired under low nutrient conditions. No significant changes were observed between the wild-type and the tagged strain. The survival fitness studies indicated the incorporation of the gfp gene did not have any noted detrimental effects on the survival and behaviour of the tagged strains. These tagged strains could therefore be used to study the fate and survival of Salmonella in biofilms of drinking water distribution systems. Genetic tagging of the target organism with the gfp gene, encoding the green fluorescent protein, allows in situ detection of undisturbed cells and is ideally suited for monitoring Salmonella as a monospecies or in a complex mixed community. The fate and persistence of non-typhoidal Salmonella in drinking water biofilms was investigated. The ability of Salmonella to form biofilms independently and the fate and persistence of Salmonella in an aquatic biofilm was examined. </p.> In monoculture S. Typhimurium formed loosely structured biofilms. Salmonella colonized established multi-species drinking water biofilms within 24 hours, growing to form micro-colonies within the biofilm. S. Typhimurium was also released at high levels from the drinking water-associated biofilm into the flow, and was seen to re-colonize elsewhere. Results showed that Salmonella can enter into, survive and grow within, and be released from a drinking water biofilm. Once Salmonella has entered into a distribution system, it will be able to colonize an existing biofilm, grow in it and be released into the flow for re-colonization elsewhere, and possible subsequent infection of consumers.
Dissertation (MSc (Microbiology ))--University of Pretoria, 2007.