The use of fecal indicators such as Escherichia coli has been proposed as a potential tool to characterize
microbial contamination of irrigation water. Recently, not only the type of microbial indicator but also
the methodologies used for enumeration have been called into question. The goal of this study was to
assess the microbial quality of different water sources for irrigation of zucchini plants by using E. coli as
an indicator of fecal contamination and the occurrence of foodborne pathogens. Three water sources
were evaluated including reclaimed secondary treated water (RW-2), reclaimed tertiary UV-C treated
water (RW-3) and surface water (SW). The suitability of two E. coli quantification techniques (plate count
and qPCR) was examined for irrigation water and fresh produce. E. coli levels using qPCR assay were
significantly higher than that obtained by plate count in all samples of irrigation water and fresh produce.
The microbial quality of water samples from RW-2 was well predicted by qPCR, as the presence of
foodborne pathogens were positively correlated with high E. coli levels. However, differences in the water
characteristics influenced the suitability of qPCR as a tool to predict potential contamination in irrigation
water. No significant differences were obtained between the number of cells of E. coli from RW-2 and
RW-3, probably due to the fact that qPCR assay cannot distinguish between viable and dead cells. These
results indicated that the selection of the most suitable technique for enumeration of indicator microorganisms
able to predict potential presence of fecal contamination might be influenced by the water
characteristics.