Monitoring generic Escherichia coli in reclaimed and surface water used in hydroponically cultivated greenhouse peppers and the influence of fertilizer solutions

Systematic monitoring of indicator microorganisms, such as Escherichia coli, can help to identify potential risk factors for faecal contamination in the agricultural environment. In this study, levels of E. coli in irrigation water (both reclaimed and surface water), water sprayed in humidifiers to regulate ambient humidity, and pepper fruits were assessed in a commercial greenhouse of hydroponically cultivated crops. Additionally, the role of fertilizer solutions as a potential vector of contamination was investigated. Lab-scale studies were also performed to evaluate the influence of fertilizer solutions on the growth/survival of E. coli in irrigation water. As expected, higher levels of E. coli were detected in reclaimed water compared with surface water. No link between E. coli prevalence in irrigation water and presence in fruit could be established. Regarding the fertilizer solutions, E. coli was detected more frequently and in higher levels in the fertilizer solution richer in micronutrients. Low concentrations of E. coli were also present in pulverized water sprayed inside the greenhouse to control humidity. In lab-scale experiments, E. coli showed potential for surviving but not for growing in most fertilizer solutions and irrigation water. Fertilizer solution of HNO3, was the only solution in which no E. coli were able to survive in the irrigation head and a rapid inactivation was observed in lab-scale tests. These results suggest that there is a low risk of contamination in this agricultural system despite the combination of higher risk irrigation water sources (reclaimed and surface water) and the hydroponic growing system. Nevertheless, special care should be taken regarding the microbiological quality of the agricultural solutions in direct contact with the edible parts of the crop.