Detection of Shiga Toxin-Producing Escherichia Coli and Salmonella Aerosolized In Various Areas of Commercial Slaughter Plants by Using Dynamic Bioaerosol Monitoring Techniques

Generation of bioaerosols containing bacterial pathogens during beef harvesting is an important issue to consider when controlling pathogens in the meat industry. Pathogens such as Shiga toxin-producing Escherichia coli (STEC) and Salmonella present on carcasses may be aerosolized during initial steps of slaughter, where highly active procedures are conducted, and transferred from these dirty areas to cleaner areas. This may result in the pathogens being deposited on the meat before the end product is released for sale. In this study, large air samples (2.8-4.8 m3) were collected from various areas at two large and two small beef harvesting establishments during the fall spring and summer seasons using a wetted wall cyclone (WWC) sampler. Samples were tested for STEC and Salmonella and analyzed by direct plating, automated immunoassay system (Crystal Diagnostic, CDx), and real-time PCR (RT-PCR) analysis. All positive samples from CDx were confirmed by plating in selective and differential media followed by biochemical and serological tests, and STEC was confirmed by conventional PCR. Positive isolates were further confirmed using BAX PCR System. The RT-PCR products were confirmed by Illumina Sequencing. Based on selective plating, there were no positive air samples for Salmonella or STEC in the fall season, while air samples from all plants were positive for Salmonella and STEC in the spring and summer. The recovery of both pathogens was improved by extending enrichment time from 18 to 36 h. Percentages of positive samples when enriching for 18 h were 21.4 and 17.9 for Salmonella and STEC, respectively. When enriching for 36 h, percent positives were 57.1 and 60.7 for Salmonella and STEC, respectively. The percent positives when testing both Salmonella and STEC by RT-PCR (37.5%, 65.0%) were significantly higher than CDx with enrichment for 18 h (P