Purpose: To evaluate Listeria enrichment broth (LEB), Half-Fraser Broth (HFB) and analytical sample volume for the detection/recovery of Listeria spp. at RAC handling facilities using automated Atlas molecular detection (Roka Bioscience) and culture-based methods.
Methods: Four hundred forty-five sterile sponges and swabs were collected from seven RAC facilities. One hundred eighteen samples were placed in 190 ml of HFB and incubated at 37°C for 24 hours. Three hundred twenty-seven samples were enriched in 90 ml of supplemented LEB and incubated at 37°C for 48 h. Following incubation, 12 µl (validated volume) were subjected to Atlas-Listeria protocols. In addition, 400 µl (sediments and highly oxidized organic matter) were evaluated in 161 paired samples. After incubation, CHROMagar Listeria incubated at 37°C for 24 - 48 h was used for confirmation of Listeria spp. with qPCR using 23S rDNA and hlyQ gene targets for Listeria spp. and L. monocytogenes, respectively.
Results: A total of 172 (38.4%) samples were positive for Listeria spp. Forty-seven of the positive samples were enriched in HFB (39.8%) and 125 in LEB (38.2%). Listeria spp. was isolated from 97 of 172 positive samples (56.4%). Forty-two strains were confirmed as L. monocytogenes (43.2%). The molecular detection of Listeria could be affected by the volume used to inoculate the Roka Atlas transfer tube. When 400 µl were used 71 of 161 samples were positive, in contrast 59 paired samples were positive with a 12 µl analytical sample.
Significance: The results of this study contribute to improved Listeria detection and recovery. The use of supplemented LEB without primary enrichment was effective for environmental detection of Listeria in these complex matrices.