Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2011
Publication Date: 3/1/2012
Citation: Pachepsky, Y.A., Morrow, J., Guber, A.K., Rowland, R.A., Shelton, D.R. 2012. Effect of biofilm in irrigation pipes on the microbial quality of irrigation water. Letters in Applied Microbiology. 54(3):217-224. Interpretive Summary: Irrigation water is recognized as a probable source of pathogenic organisms that are responsible for food-borne outbreaks. Biofilms in irrigation water delivery systems are suspect as potential reservoirs of pathogenic bacteria. However, no peer-reviewed research has been performed to evaluate the effect of biofilms present in irrigation systems on the microbial quality of water going through the pipes. We performed experiments on a sprinkler irrigation system, including simultaneous sampling of water at the intake from a creek, water from the sprinklers, water left in pipes from previous irrigation, and sampling of biofilms attached to the pipe inner surface. Samples were analyzed for E. coli concentrations. Differences in E. coli concentrations between intake and sprinkler water were observed indicating that E. coli attached to inner pipe surfaces. In addition, E. coli were isolated from pipe surfaces consistent with attachment and/or growth.. This is the first report on the potential significance of biofims in irrigation systems impacting microbial quality of irrigation waters. This is important for produce preharvest management in that it indicates the need to monitor quality of water coming from sprinklers, as well as the source waters. These results suggest that strategies maybe be required to mitigate possible pathogen accumulation on pipe surfaces and subsequent transmission to produce with irrigation water.
Technical Abstract: Aim: To test the hypothesis that microbial quality of irrigation water can be substantially altered by the association of E. coli with pipe lining in irrigation systems. Methods and Results: The sprinkler irrigation system was outfitted with coupons that were extracted before four 2-hour long irrigations carried out with weekly intervals. The intake creek water, water from sprinklers, water left in pipes from previous irrigation, and pipe lining from the coupons were analyzed for Escherichia coli. High E. coli concentrations in water remaining in irrigation pipes between irrigations indicated the opportunities for E. coli growth. In two of four irrigations the probability of the sample source, i.e. creek vs. sprinkler, being non-influential factor was only 0.14. The population of bacteria associated with pipe lining was estimated to be larger than in water in first three irrigation events and close to one in the fourth event. Conclusion: The lining-associated E. coli cannot be neglected when a mass balance of bacteria in the irrigation system is estimated. Significance and Impact of the Study: This work is the first report on the potential significance of pipe lining in microbial quality of irrigation waters. Flush of the irrigation system may be a useful management practice to decrease the risk of microbial contamination of produce. Because the microbial water quality can be substantially modified while water is transported in an irrigation system, it becomes imperative to monitor quality of water coming from sprinklers rather than at the intake, and, id necessary, to look for technologies to improve the quality of water coming from sprinklers.