Purpose: To study the effect of sampling frequency, depth, and timing relative to disturbance events on the presence of indicator (E. coli and Enterococcus spp.) and pathogenic (Salmonella and STEC) organisms on surface waters used for frost protection/irrigation.
Methods: Over 12 weeks, 216 one-gallon water samples were collected from surface water used for frost protection/irrigation. Every 2 weeks, samples were taken at 36 locations at 0, 5, 10, and 15 m away from the irrigation water intake and at 3 depth ranges; 0.5 - 1, 1.75 - 2.25, and 3 - 3.5 m below the water surface. Water was filtered using a modified Moore swab system and quantitative/qualitative recovery of indicator and pathogenic microorganisms was achieved via selective/differential culturing methods and probe-based PCR systems.
Results: Salmonella and STEC were recovered from multiple water sampling events despite all 216 one-gallon samples having populations of generic E. coli on average 3 fold below (P < 0.05) the proposed GM and STV. Significant increases in the number of positive samples for Salmonella was determined on sampling dates that coincided with rain events (P < 0.05), but marginally for indicator microorganisms. Salmonella was detected on samples coming from depths between 1 and 2.25 m. Although, marginally higher populations of generic E. coli and Enterococcus (P < 0.05) were observed between 3 - 3.5 m. Yet these populations were 3 fold below the GM and STV proposed by FSMA.
Significance: Our findings suggest that the newly proposed microbial water standard within FSMA needs to be reassessed to ensure pathogen free water and fresh produce safety.