Purpose: Identifying and monitoring the presence of coliform bacteria, generic E. coli, Salmonella and Shiga toxigenic E. coli (STEC) in rainwater catchment systems.
Methods: Over multiple growing seasons beginning in September 2013, water for irrigation of lettuce and tomatoes was collected weekly and then a twice monthly from three rainwater catchment tanks located at the Organic Crops Unit of the University of Tennessee Knoxville, which supply water to three respective high tunnels with drip irrigation systems. Coliform bacteria and generic E. coli populations were determined via most probable number assessment using Colilert® Quanti-Tray 2000. STEC and Salmonella presence was also monitored by filtering 50 and 100 ml samples through 0.45 μm membranes, which were then plated on STEC CHROMagar™ or XLT4, respectively.
Results: From September 2013 to October 2014, average total coliform counts between the three tanks were 2.53 log CFU/100 ml, with an average generic E. coli population at 0.65 log CFU/100 ml. Average STEC populations were 0.84 log CFU/100 ml. A weak correlation between STEC and generic E. coli populations (R2 = 0.51; P < 0.02) as well as between STEC and total coliform count (R2 = 0.44; P < 0.05) was shown. Salmonella were not detected in any water samples.
Significance: Coliform bacteria, generic E. coli, and STEC were detected in a rainwater catchment system evaluated over the course of a year, indicating the potential for produce contamination. The presence of pathogens demonstrates the need for routine water testing and implementation of mitigation strategies with these systems. A weak correlation between STEC and both indicator organisms suggests that improved water testing methods are necessary.