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Fig. 1 | BMC Microbiology

Fig. 1

From: Comparison of three neutralizing broths for environmental sampling of low levels of Listeria monocytogenes desiccated on stainless steel surfaces and exposed to quaternary ammonium compounds

Fig. 1

Three sets of experiments were performed in this study. The first set compared the three neutralizing broths without using Whisper™ V, a quaternary ammonium compound (QAC)-based sanitizer. The second set compared the three neutralizing broths by exposing inoculated Lm to QAC. Two quat concentrations were used, 400 ppm and 8000 ppm to represent a common concentration and a very high concentration. A pilot experiment was performed before this one to determine the appropriate combinations of Lm inoculum level and quat concentration that could yield fractional positive results in an AOAC validation scheme. After sponge sampling, three storage conditions were used to mimic same day sampling and enrichment-based analysis (i.e., 2 h at RT), enrichment-based analysis after overnight delivery of environmental samples (24 h at 4 °C) and enrichment-based analysis after over-the-weekend delivery of environmental samples (72 h at 4 °C). For the first two sets of experiments, three transport broths were stored at 4 °C before the experiments. The third set of experiments evaluated the stability of Letheen broth and HiCap broth stored at RT before sampling. Two separate evaluations were used because the inoculation levels and quat concentrations suitable to evaluate the two broths were different. The first one compared Letheen broth stored at RT and at 4 °C with D/E broth stored at 4 °C, and the second one compared HiCap broth stored at RT and at 4 °C with D/E broth stored at 4 °C. For the first and third set of experiments, we did not perform the analysis simulating the scenario of storing the sponge samples at 4 °C for 24 h due to logistical reasons

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