Bacteroidalesas a Fecal Contamination Indicator in Fresh Produce Industry: A Baseline Measurement

Abstract

Foodborne outbreaks caused by fecal contamination of fresh produce represent a serious concern to public health and the economy. As the consumption of fresh produce increases, public health officials and organizations have pushed for improvements in food safety procedures and environmental assessments to reduce the risk of contamination. Visual inspections and the establishment of "buffer zones" between animal feeding operations and producing fields are the current best practices for environmental assessments. However, a generalized distance guideline and visual inspections may not be enough to account for all environmental risk variables. Here, we report a baseline measurement surveying the background Bacteroidales concentration, as a quantitative fecal contamination indicator, in California's Salinas Valley. We collected a total of 1632 samples from two romaine lettuce commercial fields at the time of harvesting through two seasons in a year. The Bacteroidales concentration was very low (0 - 2.00 copies/cm^2). Furthermore, we established a practical methodology for evaluating the risk of fecal contamination in a real-world setting, complementing the current environmental assessment practices. This method can identify site-specific risks and offer fresh produce stakeholders a more comprehensive understanding of their fields. We anticipate this work can encourage the use of Bacteroidales in the fresh produce industry to monitor fecal contamination and prevent future foodborne outbreaks.

A portable, easy-to-use paper-based biosensor for rapid in-field detection of fecal contamination on fresh produce farms

“…The two positive controls had a mean y-value of 1.34 %positivity/min (> 0.75 %positivity/min) and were determined to be positive by the image analysis algorithm (mean positivity percentage 90.26%). These findings are consistent with our expectation that well-managed commercial fields have a low risk of fecal contamination, and therefore the concentration of Bacteroidales in the environment should be low (Wang, Ranjbaran, & Verma, 2023). However, trace amounts of Bacteroidales DNA may be present in the field due to various reasons, such as the use of organic fertilizer or residuals from previous contamination.…”

“…Bacteroidales as a FIB has been extensively used to evaluate fecal contamination both in fresh produce fields and for water quality monitoring (Jiang et al, 2018; Mascorro et al, 2018; Ravaliya et al, 2014; Wang, Ranjbaran, Ault, et al, 2023). In the previous studies, we have determined that there is a ∼10 4 -fold difference in Bacteroidales concentration between fields with a high risk of fecal contamination (adjacent to animal units) (Wang, Ranjbaran, Ault, et al, 2023) and a low risk of fecal contamination (commercial fresh produce fields) (Wang, Ranjbaran, & Verma, 2023). The significant difference in Bacteroidales concentrations between “high risk” and “low risk” fields makes it a valuable tool for researchers and industry stakeholders to monitor fecal pollution and facilitate microbial safety in the fresh produce industry.…”

“…Aside from determining the presence or absence of pathogens, an alternative is to quantify the abundance of fecal indicator bacteria (FIB)—microorganisms selected as indicators of fecal contamination (Brauwere et al, 2014; Wang, Ranjbaran, Ault, et al, 2023). FIB such as Escherichia coli , Enterococcus faecalis , and Bacteroidales , have been used to assess possible fecal contamination in fresh produce (Denis et al, 2016; Drozd et al, 2013; Harris et al, 2017; Ordaz et al, 2019; Wang, Ranjbaran, & Verma, 2023). Compared to other FIB, Bacteroidales is preferable due to the following four features: i) high prevalence in feces (constituting 30%–40% of total fecal bacteria, 10 9 to 10 11 CFU/g), ii) low natural abundance from non-fecal sources, iii) obligate anaerobicity (preventing their growth and multiplication in the ambient environment), and iv) high host specificity (host-specific markers on the 16S rRNA gene can be used for microbial source tracking) (Mascorro et al, 2018; Ordaz et al, 2019).…”