Investigation of the Impact of and Novel Intervention Technologies for Protozoan Parasites on Fresh Produce and in Water

Abstract

Protozoan parasites are neglected pathogens of concern. Cryptosporidium spp., Cyclospora cayetanensis, Giardia intestinalis, and Toxoplasma gondii cause 678,828; 11,522; 1.12 million; and 173,415 cases of domestically acquired illness in the United States each year, respectively. Protozoan parasites are typically transmitted by the fecal-oral route, through consumption of contaminated food, water, and soil. Each year, 8%, 99%, 7%, and 50% of domestically acquired cases associated with Cryptosporidium, Cyclospora, Giardia, and Toxoplasma, are attributed to contaminated food, respectively. Although many past outbreaks have been attributed to contaminated drinking and recreational water, there is growing evidence to suggest that protozoa are becoming more common contaminants of fresh produce. This is particularly concerning due to the robust nature of these microorganisms, which can remain viable after various postharvest interventions, such as chlorine baths, cleaning, and blast chilling. In addition, the sensitivity of fresh produce to quality degradation prevents the application of many hurdles and technologies that inactivate protozoa due to concerns about quality. The extent to which protozoa impact the produce industry is not well understood. Protozoan parasites are also often neglected from primary food safety considerations. This is due, in part, to their complex and diverse lifecycles, and gaps in scientific knowledge critical to providing guidance for growers and informing prevention and intervention strategies in produce production and processing. This emphasizes the importance of environmental surveillance and evaluation of novel intervention technologies targeting protozoan parasites. As produce-associated outbreaks attributed to protozoan parasites have increased, the importance of irrigation water as a critical resource and a vehicle for contamination of produce has become clear. Groundwater resources for irrigation are finite and non-traditional alternatives to groundwater will be essential to sustainably meet the needs of the agricultural industry. It is imperative that the microbial quality of non-traditional water is evaluated for protozoan parasites prior to use in irrigation. Environmental surveillance at three reclaimed and three surface water sources in the Mid-Atlantic region from June 2017 to October 2018, indicated Cryptosporidium, Giardia, and Toxoplasma (oo)cysts were detected in both reclaimed (40.9%, 27.3%, 9.1%; n=22) and surface (34.0%, 2.0%, 10.0%; n=50) water samples, respectively. Overall Cryptosporidium was detected most frequently (36.1%) of the protozoa evaluated. There was not a significant association with season and evaluated protozoa (p>0.13). The detection of Cryptosporidium and Giardia was not significantly associated with precipitation (p>0.09) but was significantly associated with ambient air temperature (p<0.03). Toxoplasma detection was associated with precipitation, chloride concentration, and conductivity of the water (p<0.03). Current postharvest practices are not sufficient to inactivate protozoa on or in produce and water. Cilantro has been identified as a vehicle for protozoan illness. Cold plasma (CP) is an emerging nonthermal waterless technology with potential applications in food processing. In these studies, the impact of CP treatment on the viability of Cryptosporidium parvum (C. parvum) oocysts inoculated onto cilantro was investigated. Studies performed with CP on C. parvum oocysts inoculated onto cilantro showed overall, each CP treatment significantly reduced oocyst infectivity compared to the 0-s treatment control (p < 0.02). Log inactivation of oocysts observed on cilantro were 0.84, 1.23, and 2.03 for the 30-, 90-, and 180-s treatment times, respectively. Drying and darkening of cilantro leaves was observed with treatments longer than 30 s. CP can reduce C. parvum infectivity on cilantro. Pulsed light (PL) is an emerging technology with potential applications in food processing as well. The impact of PL treatment on the viability of C. parvum oocysts inoculated onto cilantro, mesclun lettuce, spinach, and tomatoes was investigated. Studies performed with PL on C. parvum oocysts inoculated onto raw agricultural commodities, showed that maximum log reductions achieved on cilantro, mesclun lettuce, spinach, and tomato were 2.46, 4.27, 2.51, and 2.19, respectively. Significant changes in color values were not observed for leafy greens or herbs; however, wilting was observed in samples treated longer than 10 s. Significant change in the b* value for tomato treated for 90 s was observed. PL can reduce the infectivity of C. parvum oocysts on cilantro, mesclun, lettuce, spinach, and tomato. Collectively these studies indicate that non-traditional agricultural water sources are susceptible to contamination with protozoan parasites and that with further optimization, CP and PL treatment technologies have potential applications in postharvest processing of a variety of commodities to reduce food safety risks associated with protozoan parasites.