Antimicrobial Incorporated Multi-Angle Light Scattering Spectroscopy (ANIMALS) Facilitates Detection of Escherichia Coli O157:H7 in Large Volumes of Irrigation Water

Contaminated irrigation water has been shown to be an important vehicle for transfer of Escherichia coli O157:H7 to produce. Timely detection of this pathogen in irrigation water can prevent contamination of the final product, and such detection should integrate concentration of pathogens from large volumes of water. Antimicrobial Incorporated Multi-angle light scattering spectroscopy (ANIMALS) is a recently developed method for rapid detection of foodborne pathogens. The objective of this study was to use the ANIMALS method to rapidly detect E. coli O157:H7 in large volumes of irrigation water. River water and reservoir samples were artificially contaminated with a 3 strain cocktail of E. coli O157:H7 at four concentrations including 100 to 103 CFU/ml). Following concentration by Modified Moore swab and continuous centrifugation, up to 50 ml of the concentrates were further concentrated by immunomagnetic separation (IMS) and incubation in the presence (test samples) or absence (control samples) of a 37 strain bacteriophage cocktail (specific for E. coli O157:H7) in 10 ml of tryptic soy broth + 20 µg/ml novobiocin at 42º C. ANIMALS measurements were taken in a SpectraPoint light scattering machine (SpectraDigital) at 4, 6, 8 and 10 hours. Light scattering spectra of samples incubated with the bacteriophage cocktail differed markedly from non-bacteriophage treated samples that were used to obtain reference (control) spectra. An algorithm was developed to evaluate the area under the curve of all spectra. The means and standard deviations of the ratios of the differences between the test and reference spectra for the four concentrations (100 to 103 CFU/ml) of E. coli O157:H7 were analyzed as well as for negative controls (samples of river or reservoir water that were not inoculated with E. coli O157:H7). E. coli O157:H7 was consistently detected at concentrations from 101 to 103 CFU/ml in spiked river water within 8 hours (p< 0.05). All concentrations (100 to 103 CFU/ml) were detected after 10 hours of enrichment (P<0.05). These results demonstrate the ability of ANIMALS to rapidly and sensitively detect the presence of E. coli O157:H7 in water used for irrigation of produce, even against a high number of background microflora.