Zeitschrift für Lebensmittel : Mikrobiologie, Sicherheit und Hygiene
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Evaluation of Total Bacteroides sp., as an Alternative Indicator in Agricultural Water Quality

Valerisa Joe-Gaddy*, Natalie Brassill, Dametreea Carr, Jean McLain, Channah Rock

Pre harvest irrigation water represents a key potential source of pathogenic bacteria during the production of fresh produce. Industry guidance metrics uniformly identify generic Escherichia coli (E. coli) as a practical and cost‐effective indicator of fecal contamination in water. Although generic E. coli satisfies most characteristics of an ideal bacterial indicator, very limited correlation exists between the presence of E. coli, pathogen presence, and microbial risk to consumers following consumption. The Food Safety Modernization Act’s Produce Safety Rule’s Microbial Water Quality Profile is under abeyance due to concerns that there is not enough scientific evidence to support the rule in its’ current form; thus, it is important to examine feasible alternative indicator organisms which could improve agricultural water quality assessment and the protection of public health.

This work examines the bacterial group, Bacteroides for prediction of pathogens in irrigation water samples (n=98) collected throughout Southern Arizona. Total Bacteroides sp. molecular markers were enumerated by quantitative Polymerase Chain Reaction, using: 1) a non- pathogenic Bacteroides sp. protocol (AllBac) published in the peer- reviewed literature and 2) a commercially available Pathogenic Bacteroides sp. enumeration kit (Primerdesign™ Ltd. Pathogen Bacteroides). Additionally, each water sample was culturally assayed for generic E. coli using EPA-approved Colilert® to assess correlations between E. coli, Bacteroides sp. markers and pathogens. Samples were additionally analyzed using Atlas® System Roka Biosystem to determine absence/presence of pathogenic E. coli O157:H7, STEC and Salmonella. Out of 98 samples, 31 tested positive for E. coli, but only 11 of the 31 samples exceeded the generic E. coli guideline of GM 126 MPN/100 mL for agricultural water. Results of the Allbac and Primerdesign™ Ltd. Pathogen Bacteroides sp. kit were then compared against the IDEXX Colilert-18© using linear regression to identify relationships between the two. The regression results were significant, p-value <0.02, suggesting that the assays for Bacteroides sp., performed as well as that for generic E. coli. However, the use of generic E. coli as an indicator (IDEXX), in this study, failed to ‘indicate’ pathogens in 80.6% of samples that were positive for pathogenic E. coli and/or Salmonella by ROKA, highlighting the well-established unsuitability of E. coli as an indicator.