Validation of the MicroSnap Coliform and E. coli Test System for Enumeration and Detection of Coliforms and E. coli in a Variety of Foods.

Abstract

The MicroSnap Coliform and E. coli system was devised to give rapid enumeration and detection of coliforms and/or Escherichia coli strains in a sample of food within an 8 h working shift. The method measures β-galactosidase and β-glucuronidase enzymes using novel bioluminogenic substrates which develop an output light signal proportional to the concentration of enzyme discovered. The assay uses two different phases to determine the enzyme concentration. The first phase is an enrichment of the sample in a nutrient-rich broth device at 37 ± 0.5°C. After 6 or 8 h, an aliquot is taken from the enrichment device and injected into the Coliform Detection Device, which is assayed in a luminometer after 10 min of incubation at 37 ± 0.5°C. Samples testing positive in the Coliform Detection Device can be subsequently assayed specifically for E. coli using the E. coli Detection Device. The relative light unit output from the detection device is proportional to the bacterial concentration when the incubation was initiated, which is proportional to the contamination level in the matrix being assessed. The MicroSnap Coliform and E. coli system was evaluated for both quantitative and qualitative analysis of coliforms and E. coli in a variety of foods. Three different luminometers were used in the analysis, each of which has different functionalities and different sensitivities. The MicroSnap method showed good correlation with the appropriate corresponding reference method for enumeration of coliforms and E. coli. A statistically significant difference was seen in detection of E. coli in milk, as reported by the independent laboratory. The reference method reported higher mean Log10 CFU counts than the MicroSnap method; however, no significant differences were seen between the MicroSnap system and reference methods for any of the other matrixes. Inclusivity testing was conducted on 25 different non-E. coli coliforms and 25 different E. coli strains, and exclusivity testing was conducted on 30 different species of nontarget organisms. Two E. coli strains were not detected in the Coliform Detection Device after 8 h on one of the instruments. All other inclusivity strains tested were detected after 8 h of incubation. None of the exclusivity strains were detected. The lot-to-lot and kit stability studies showed no statistical differences between lots or over the term of the shelf-life. Robustness studies indicate that the timing of incubation for the detection phase is critical for correct system functioning.