Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2007
Publication Date: 4/30/2008
Citation: Orozco, L., Iturriaga, M., Tamplin, M., Fratamico, P.M., Call, J.E., Luchansky, J.B., Escartin, E. 2008. Animal and Environmental Impact on the Presence and Distribution of Salmonella spp. in Hydroponic Tomato Greenhouses. Journal of Food Protection. 71(4):676-683. Interpretive Summary: Tomatoes contaminated with Salmonella, a pathogenic food-borne bacterium, have been identified as vehicles of human diarrheal illness known as salmonellosis. Contamination of tomatoes can occur at several points from farm to table. Therefore, an investigation examining the sources of Salmonella contamination of tomatoes grown in hydroponic greenhouses in Queretaro Mexico was conducted. The presence of Salmonella was determined on samples of tomatoes, water, soil, sponges, gloves, animal feces, and from the hands and shoes of farm workers. Salmonella was detected in all types of samples, except workers’ gloves and hands. Methods were used to determine the characteristics of the Salmonella bacteria isolated from the various sources, and a method known as pulsed field gel electrophoresis was used to track the spread of Salmonella contamination from the different sources to the tomatoes. Several types of Salmonella bacteria that have been associated with human illness were identified. Animals, including opposums, mice, and goats and workers’ shoes were identified as important sources of contamination of the tomatoes. Furthermore, there was a higher incidence of Salmonella in the greenhouses and on tomatoes during and after a flood, which resulted in water runoff entering the greenhouses. The study demonstrated that contamination of tomatoes grown in hydroponic greenhouses can occur from various sources, and critical control points from farm to table need to be identified to develop strategies to prevent contamination.
Technical Abstract: From 2003 to 2004, we studied the impact of environmental influences on the microbiological quality of a hydroponic tomato farm. The presence of Salmonella was investigated on 906 samples of tomatoes and 714 environmental samples. The farm comprised 14 greenhouses and a technologically advanced packing house. It was operated under a Sanitary Agricultural Practices (SAPs) plan. The objective of the present study was to determine the operating sources of contamination. During the course of the study, two independent natural events affected the farm. In 2003, water runoff entered some of the greenhouses. A year later, wild animals gained entry into several of the greenhouses. Salmonella and Escherichia coli were found in samples of tomatoes, water puddles, soil, shoes, and the feces of local wild and farm animals. S. Montevideo, S. Newport, and strains of the F serogroup were isolated from tomatoes. Almost all of the S. Newport strains were isolated from samples collected during or immediately after the flood. Analysis by pulsed-field gel electrophoresis (PFGE) revealed that some S. Montevideo isolates from tomatoes, opossums, and mice displayed identical XbaI or AvrII patterns, suggesting that these wild animals represented one source of contamination. F serogroup strains were found mostly on samples of goat feces and personnel shoes when standard working practices were in place. Shoes were found to be an important vehicle for dissemination of Salmonella into the greenhouses. The level of protection provided by hydroponic greenhouses does not exclude the eventuality that enteric pathogenic bacteria can gain access through various avenues.