Comparison of methods to determine the microbial quality of alternative irrigation waters

Authors: HSIN-BAI, YIN - University Of Maryland; Patel, Jitu

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2018
Publication Date: 2/3/2018
Citation: Hsin-Bai, Y., Patel, J.R. 2018. Comparison of methods to determine the microbial quality of alternative irrigation waters. Agricultural Water Management. 201:38-45. https://doi.org/10.1016/j.agwat.2018.01.012.
DOI: https://doi.org/10.1016/j.agwat.2018.01.012

Interpretive Summary: The availability of water for crop irrigation is decreasing due to droughts, population growth, and pollution. Implementation of the Food Safety and Modernization Act (FSMA) for irrigation water standards discourages growers from using poor microbial quality water for produce crop irrigation. We evaluated the microbial quality of alternative water sources including reclaimed water (RCW), roof-harvest rainwater (RHW), and creek water (CW) to ascertain if they met the FSMA microbial quality criteria for agricultural water as well as to analyze for potential pathogenic bacteria. Prevalence of fecal bacterial populations and pathogens in water were analyzed by the membrane filter technique and using an innovative concentrator analysis method. Presumptive pathogens were confirmed using genetic methods. In total, 25 samples of alternative water were analyzed including 7 RCW, 9 RHW, and 9 CW. Escherichia coli populations from all RHW and CW samples were below the FSMA criteria (126 Colony Forming Units/100 ml). No significant difference between the two detection methods was observed when enumerating total coliform and enterococci bacteria. Salmonella were recovered in 3 RCW, E. coli O157:H7 in 1 RHW and 2RCW, and Listeria monocytogenes was recovered in 1 RHW and 3 CW samples. Results suggest that RCW requires remediation treatment to reduce bacterial populations prior to use for irrigation of fresh produce. CW and RHW water quality met the FSMA standards for irrigation; however, pathogens present in this water may contaminate fresh produce during irrigation and may cause foodborne illnesses when fresh produce is consumed.

Technical Abstract: The availability of water for crop irrigation is decreasing due to droughts, population growth, and pollution. Implementation of Food Safety and Modernization Act (FSMA) for irrigation water standards discourages growers to use poor microbial quality water for produce crop irrigation. We evaluated microbial quality of alternative water including reclaimed water (RCW), roof-harvest rainwater (RHW), and creek water (CW) to detect bacterial pathogens and to ascertain if it meets FSMA microbial quality criteria as agricultural water. The alternative water quality was assessed by monitoring the populations of fecal indicators such as Escherichia coli, enterococci, total and fecal coliforms; and bacterial pathogens (Salmonella, Listeria monocytogenes, and E. coli O157:H7). Water samples were analyzed by two analysis methods including the membrane filter technique and an innovative concentrator analysis. Briefly, 100 ml of each water sample was filtered with 0.45 µm membrane filter using the vacuum manifold or concentrated to ~250 µl using the concentrator and were directly enumerated on specific agars. Bacterial populations were recorded after incubation and expressed as log CFU/100 ml. Presumptive pathogens were confirmed by real-time quantitative PCR. In total, 25 samples of alternative water were analyzed including 7 RCW, 9 RHW, and 9 CW. Escherichia coli populations from all RHW and CW samples were below the FSMA criteria (2.1 log CFU/100 ml). No significant difference between two detection methods was observed when enumerating total coliforms and enterococci. Salmonella were recovered in 3 RCW, E. coli O157:H7 in 1 RHW and 2RCW, and Listeria monocytogenes was recovered in 1 RHW and 3 CW samples. Results suggest that RCW requires remediation treatment to reduce bacterial populations prior to use for irrigation of fresh produce. CW and RHW water quality meets FSMA standards for irrigation; however, presence of pathogens in this water may cause foodborne illnesses when fresh produce is consumed.