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. Key words: Internalization, enteric pathogens, human excreta, coriander, rhizosphere.
Highlights
A major challenge experienced in informal urban settlements is sanitation which has negative impact on environment and public health
Internalization of microorganisms via plant roots from pathogen spiked soil At the onset of the experiment (t=0), the A. lumbricoides eggs recovered from the human excreta slurry and soilslurry mix were 100% viable
Presence of the pathogens from human excreta on plants surface and tissue When human excreta slurry was mixed with soil and used to grow coriander, A. lumbricoides (200 eggs/g of soil) at viability of 20% were recovered from the soil at harvest; none was found attached to any of the tested plants’ parts
Summary
A major challenge experienced in informal urban settlements is sanitation which has negative impact on environment and public health. Regardless of the route that bacteria are introduced to the plant, including; irrigation water, soil or manure, the bacteria has the ability to establish and colonize the plants rhizosphere with the ability to migrate in plant system (Ongeng et al, 2015; Lim et al, 2014; Ongeng et al, 2011; Warrier et al, 2003) Some of these bacteria have the ability to withstand antibiotics and survive well in the plants rhizosphere as they utilize roots exudates as source of carbon which withstand osmotic pressure in rhizosphere environment (Berg et al, 2005; Ongeng et al, 2015; Yang et al, 2001)
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