Purpose: To demonstrate the performance of MicroSnap Surface Express Listeria for real-time detection of Listeria from environmental surfaces.
Methods: Stainless steel coupons were inoculated with 100uL of a mixture of 4 Listeria species (monocytogenes, welshmeri, innocua and ivanovii) in BPDW. The coupons were dried overnight and swabbed with MicroSnap Surface Express Listeria ; test devices were then incubated for 24 hours and measured using the EnSURE luminometer every hour. A duplicate set of coupons were swabbed and used as reference methods Listeria petrifilm and MOX agar.
Results: The survivability from the drying process was calculated by comparing the dried with added inoculum levels, this was determined to be 0.004%. The -1 dried dilution had a mean (n=5) CFU of 83550, -2 had 8350 CFU, -3 had 830 CFU and -4 37 CFU all other dilutions discovered no colonial growth. The assays started to show a positive RLU (mean blank plus 6 standard deviations) in the EnSURE at 8 hours for -1, -2 dilution was positive at 10 hours with -3 becoming positive at 12 hours and -4 becoming positive at 14 hours. This time of flight determination prove the Listeria bacteria are actively metabolising the substrate and producing light when a threshold CFU is reached. The higher the CFU the quicker the determination of positive can be determined.
Significance: The ability to determine whether a surface is highly contaminated with Listeria in less than 24 hours revolutionizes modern Listeria environmental monitoring practices.