Microbiological profile of greenhouses in a farm producing hydroponic tomatoes

Produce, including tomatoes, has been implicated in several outbreaks of foodborne illness. A number of the sources of contamination for produce grown in open fields are known. However, as an alternative agricultural system, hydroponic greenhouses are reasonably expected to reduce some of these sources. The objective of the present study was to determine the microbiological profile of tomatoes grown in greenhouses at a Mexican hydroponic farm with a high technological level and sanitary agricultural practices (SAPs) in place. Tomatoes and other materials associated with the farm were analyzed for the presence of Salmonella enterica and populations of Escherichia coli, coliforms, and Enterobacteriaceae. Tomatoes showed median levels of 0.8 log CFU per tomato for Enterobacteriaceae, < 0.5 log CFU per tomato for coliforms, and 0.5 most probable number per tomato for E. coli. Despite the physical barriers that the facilities provide and the implemented SAPs, we found that 2.8% of tomatoes were contaminated with Salmonella and 0.7% with E. coli. Other Salmonella-positive materials were puddles, soil, cleaning cloths, and sponges. Samples from the nursery and greenhouses were positive for E. coli, whereas Salmonella was found only in the latter. Although hydroponic greenhouses provide physical barriers against some sources of enteric bacterial contamination, these results show that sporadic evidence of fecal contamination and the presence of Salmonella can occur at the studied greenhouse farm.