Purpose: The purpose of this study was to evaluate the effectiveness of sample concentration via Moore swabs (MS) or disposable inline filters (DIF) and selective enrichments to detect Salmonella spp. and E. coli O157:H7 in irrigation water using VIDAS technology.
Methods: Three-strain cocktails of Salmonella spp. or E. coli O157:H7 strains associated with produce outbreaks were used to contaminate large volumes of irrigation water (10 l) at concentrations of 0.1, 1, 10, and 100 CFU/ml. Samples were enriched pre- and post-concentration in buffered peptone water containing 8 mg/l vancomycin (E. coli O157:H7) or Salmonella supplement (Salmonella) for up to 18 hours at 42°C. Samples were tested at 8, 12, and 18 hours.
Results: Both target pathogens were detected at the lowest spiking level of 0.1 CFU/ml following concentration and enrichment for 8 hours, with a significantly higher (P < 0.001) number of samples being detected following concentration compared to non-concentrated samples. For E. coli, detection of the higher contamination levels was possible pre-concentration at 8 hours, but for Salmonella, only 100 CFU/ml could be detected pre-concentration after 18 hours of enrichment.
Significance: The results of this study show that the VIDAS technology can be used to sensitively and specifically detect Salmonella spp. and E. coli O157:H7 in irrigation water. Concentration protocols employed here greatly shortened the time-to-detection and improved sensitivity of the previously established methodology.