Internalization of enteropathogenic human bacteria in lettuce and coriander plant tissue

Abstract

The ability of plant rhizosphere and to some extent phyllosphere to support metabolism of some human enteric bacteria has been widely demonstrated. The nutrients provided by seedlings during germination support bacterial survival in tissue of growing plants. Plant rhizosphere has been described as being high in nutrients, and rhizosphere microbiomes are well adapted to this environment, enteric human pathogens when introduced to such environment face strong competition and their survival is depended on biofilm formation. Coriandrum sativum (coriander) and Lactuca sativa (lettuce) were transplanted in soil mixed with human excreta at a ratio of 40:1 containing 3log10 cfu/g soil of a mixture of human enteric pathogens, consisting of enteropathogenic Escherichia coli (EPEC), Campylobacter coli, Campylobacter jejuni and Salmonella enterica and control pots (positive and negative) were included in the experiment. At harvest, which was carried out at seven weeks after planting, soil, roots, stems and leaves were assayed for presence of enteric pathogens both on surface and in the tissue. Pathogenic E. coli and S. enterica were isolated from soil and on the surface of coriander roots. C. jejuni and C. coli were isolated from all the plant tissues. Conclusively, this study demonstrated a rarely reported internalization of C. jejuni and C. coli in coriander at seven weeks post-inoculation. It is therefore evident that use of untreated human excreta contaminated with enteric pathogens to grow edible vegetables, could pose significant food safety hazard when consumed uncooked or undercooked.