Public health food-borne illness outbreaks continue even with significant improvements in pathogen detection technologies. Produce recalls have increased in frequency in recent years. Significantly, it is evident that irrigation water used in agriculture plays an important role in potentially introducing microbial contamination. Therefore, its risk management is crucial for safety assurance of the produce supply chain.

The goal of this research is the development and optimization of a novel selective medium for sensitive screening of Shiga-toxin producing E. coli and Salmonella in irrigation water. The enrichment-indicator system developed meets the demand of a method for multi-pathogen enrichment and detection in a single assay format. The method described herein allows cost effective detection of STEC and Salmonella within 24 hours. This study details development of a facile screening technique for STEC and Salmonella in irrigation water. The m-SSS medium was inclusive of a wide range of STEC and Salmonella serotypes, while exhibiting exclusivity against common background bacteria. The incorporation of a pH indicator and a monosaccharide enabled presumptive screening of common serotypes of STEC and Salmonella. Modifications on the original medium formulation (SSS medium) were made to improve sensitivity for seven major STEC and Salmonella serotypes to comply with U.S screening standards. The developed method was applied to evaluate the microbial quality of water samples from different sources. The results suggested m-SSS was able to enrich and screen for STEC and Salmonella in diverse water samples because elevated incubation temperature increased screening selectivity of m-SSS but hindered recoveries of some Salmonella in some water samples, incubation temperatures should be adjusted to optimize for targeted pathogens.

Highlights

• A selective indicator medium was developed to screen irrigation water for contamination by STEC and Salmonella sp.
• The indicator medium was generated by removal of some selective agents and addition of a pH indicator and the carbohydrate, D-trehalose.
• The indicator medium was inclusive of all the regulated STEC serotypes and a large number of Salmonella serotypes. The medium also excluded virtually all the tested non-STEC and non-Salmonella bacteria.
• The color indicator system was shown to be effective in both spiked surface water as well with naturally occurring microflora.