Dynamics of microbial communities on spinach irrigated by ground water, reclaimed water and roof-harvest water

Irrigation water, particularly if applied overhead, could be an important source of bacterial contamination to fresh produce. The colonization, survival and proliferation of exogenous bacterial pathogens can be strongly influenced by the produce microbiota. The objective of this study is to investigate the dynamics of bacterial community on spinach after irrigation by ground water (Cr), reclaimed-waste water (Wa), and roof-collection water (Rf). Spinach was irrigated with three types of water (Cr, Wa, Rf) in two weeks in a randomized complete block design with 2 replicates (plot) for each treatment. Spinach before and after irrigation and water samples were collected for bacterial plate count, qPCR, and 16S rDNA sequencing survey analyses. The average bacterial population densities on spinach (plate count: 6.50 ± 0.04 log CFU/g; qPCR estimation: 7.40 ± 0.10 log 16S copies/g) were significantly higher than that in tested irrigation water (3.61 ± 0.12 log CFU/ml, 4.94 ± 0.13 log 16S copies/ml). The composition of bacterial communities in Cr changed between the two sampling weeks, while the composition was not significantly shifted in Wa and Rf. The dominant bacterial taxa on spinach were not significantly affected during the two-week irrigation, however, certain bacterial species were transmitted to spinach through irrigation. This study provides knowledge on the microbial ecology of diverse bacterial communites on spinach after irrigation by different types of water, which can benefit further studies on the interaction of microbes on produce, and the prevention of foodborne pathogens and plant disease.