Evaluation of aqueous chlorine and peracetic acid sanitizers to inactivate protozoa and bacteria of concern in agricultural water.

Agricultural water is a potential source of microbial contamination whereby Escherichia coli, Salmonella, Cryptosporidium, and Cyclospora cayetenensis can enter the food supply. To reduce this risk, effective sanitization of agricultural water may be critical to food safety. As such, it is important to investigate the effects of aqueous peracetic acid (PAA) and chlorine (Cl) on bacteria and protozoa at different treatment times and temperatures in agricultural water with respect to key water characteristics. Multiple concentrations of each sanitizer, ranging from 3 to 200 ppm, were prepared in recently collected agricultural water, the solution was brought to the desired temperature, and the target organisms were added and left for the desired contact time (5 or 10 minutes) when sodium metabisulfite was added to neutralize the sanitizers. Bacterial samples were enumerated on MacConkey or XLT4 agar. Samples with protozoa were added to mammalian cell culture (HCT-8 cells for Cryptosporidium parvum and MDBK cells for Eimeria tenella). After 48 hours, the infected cells were collected, DNA extracted and infectivity assessed by quantitative PCR (qPCR). Low and high concentrations of sanitizer were effective at eliminating bacteria with Cl being significantly (P < 0.05) more effective. The greatest reductions in E. coli and Salmonella (3.48 log and 2.5 log cfu/mL, respectively) were observed after 10 minutes of exposure to 10 ppm Cl. Concentrations of sanitizer 50 ppm and lower resulted in insignificant (P > 0.05) reductions in parasite infectivity of less than 1 log for both organisms. A 200 ppm PAA treatment reduced infectious oocyst populations by 3.8 log for C. parvum and 2.6 log for E. tenella, with Cl being significantly (P < 0.05) less effective against these organisms.

Importance: This research is critical to inform decisions regarding the application and use of sanitizers in pre-harvest agricultural water settings to enhance food safety. Understanding the effectiveness of chlorine (Cl) and peracetic acid (PAA) on bacteria and protozoa will allow for the more efficient and practical use of these sanitizers, thus improving agricultural practices in ways that are beneficial to both growers and consumers.