Abstract
Fresh produce outbreaks due to Shiga toxin-producing Escherichia coli (STEC) continue to occur in the United States (US). Manure-amended soils can pose a public health risk when used for growing raw agricultural commodities. Knowing the prevalence and concentration of STEC in untreated biological soil amendments of animal origin (BSAAO) is important to help guide the most appropriate pre-harvest interval(s) following application to limit risks from these soil amendments. Bovine manure samples were collected from 12 farms in Florida, including samples from piles, lagoons, barns, and screened solids. Two methods were used to detect stx1/2 and rfbE genes in samples. A prevalence rate of 9% for stx1 and/or stx2 and 19% for rfbE was observed from the 518 bovine manure samples evaluated. A most probable number (MPN) assay was performed on stx+ samples when applicable. The geometric mean for stx+ samples (n = 20) was 3.37 MPN g-1 (0.53 log MPN g-1) with a maximum value of 6,800 MPN g-1 (3.83 log MPN g-1). This research was part of a larger nationwide geographical study on the prevalence and concentration of STEC in bovine manure to help guide regulations on feasible pre-harvest intervals for the application of untreated BSAAO.
Highlights
Outbreaks due to Shiga toxin-producing Escherichia coli (STEC) are costly to the economy and can affect both the public sector as well as growers/shippers in the produce industry
There were 97 (19%) rfbE+ samples identified with the Immunomagnetic separation (IMS)-O157 method
Sample DNA that was rfbE+ was further analyzed for the presence of stx1 and stx2, and 26 additional stx+ samples were identified
Summary
Outbreaks due to Shiga toxin-producing Escherichia coli (STEC) are costly to the economy and can affect both the public sector as well as growers/shippers in the produce industry. In 2018, it was reported that confirmed and suspected foodborne incidences of STEC accounted for 203 (5%) outbreaks, 2,465 (3%) illnesses, 693 (13%) hospitalizations, and 13 (9%) deaths from 2009 to 2015 in the US (2). Prevalence of STEC in bovine manure on Florida farms. These figures include all food types, though produce-related outbreaks represent a substantial portion of the STEC foodborne outbreaks in the US [2, 3]. A STEC outbreak linked to spinach in 2006 resulted in 199 illnesses, 102 hospitalizations, and three deaths [5]. In 2018, a STEC outbreak linked to romaine lettuce exceeded the case count of 2006, resulting in 210 illnesses, 96 hospitalizations, and five deaths [6]
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