The effect of exposure to sub-lethal chlorine stress on Salmonella enterica serotypes Typhimurium and Heidelberg was examined in this study. Both serotypes demonstrated an acquired tolerance to chlorine with the adapted cells growing in concentrations above the MIC. Chlorine induced a morphological change to the rugose variant in Salmonella. The biofilm formation of the adapted and control cells was tested on food-contact surfaces at room temperature and 37°C. The chlorineapted rugose formed stronger biofilms (P < 0.05) when compared to smooth (adapted and control) on both surfaces tested and at both temperatures. The possibility of crossaptation to antibiotics and low pH was evaluated. Adapted rugose showed reduced susceptibility against some of the antibiotics tested. Chlorine does not aid in the survival of Salmonella enterica at low pH. Chlorine stress can select for tolerant Salmonella cells that attach strongly to food-contact surfaces and after some time may become less susceptible to antimicrobials.

The increase in production farming, also known as concentrated animal feeding operations (CAFOs), garners more investigations on the implications to public health regarding the disposal of the wastes of food production animals. In addition to the vast amount of animal manure produced, human biosolids is another waste residual that must be managed. The research focus was the sustainability of foodborne pathogens in waste products and the variables that manipulate these environments such as moisture, temperature, organic matter and time. The first study was designed to analyze spatial differences in microbial populations in broiler litter by investigating the relationship of intra-house location, age of flock, bedding moisture, and seasonality. Antibiogram profiles of selected isolates were explored to determine if antibiotic resistant bacteria are common in these environments and if multiple class resistance is present. These findings provided insight into new targets that may reduce zoonotic bacteria that are problematic from a food safety prospective as well as nuisance bacteria that threaten broiler health. The second study was designed to establish current decay rates of viral and bacterial pathogens when seeded in various waste residuals and the effects soil type and application method have on those rates. Decay rates were established by standard culture and molecular methods, such as qPCR. A comparison of both derived inactivation rates were analyzed to determine if these methods were significantly different. Both cultural and molecular methods have limitation and advantages, and the argument that both are useful and needed is asserted. The decay rates associated with each method were used to simulate a one-time exposure to a land application site to assess the microbial risk of Salmonella using a Quantitative Microbial Risk Assessment model.

Salmonella spp. is a human pathogen that has been reported in catfish, but with conflicting results. Salmonella spp. was isolated from live catfish, catfish products and the processing environment during catfish production, followed by evaluation of their antibiotic resistance and clonal similarities. Distinction of Salmonella spp. was increased by lowering background microflora with the addition of the antimicrobial novobiocin to the agar media. More than ten Salmonella serotypes were isolated from catfish and catfish products, such as live, chilled fillets, frozen fillets, and conveyor belts in catfish processing facilities. The isolates that were recovered include Salmonella ser. Typhimurium, Barranquilla, Mbadaka, Putten, Infantis and Thompson among others. The number of isolated Salmonella spp. and serotypes varied between sampling in catfish facilities. Clonal similarities of Salmonella spp. were found within sampling but did not show persistency among sampling periods, suggesting the opportunistic nature of the pathogen. Salmonella ser. Typhimurium was the most predominant isolate in live catfish and similarities were found within sampling but were not persistent among sampling periods. Antimicrobial resistant Salmonella was identified from the recuperated isolates. All Salmonella spp. isolates, showed resistance to erythromycin, vancomycin and rifampin regardless of the serotype, but resistant genes were absent suggesting that resistance was due to the pathogen’s biological nature. These results suggest that it is possible to recover Salmonella spp. in catfish products, but its opportunistic nature makes it difficult to predict the source or incidence of this pathogen.

Salmonella and Campylobacter are two foodborne pathogens that continue to persist in broiler processing. Various studies have demonstrated that peracetic acid can effectively reduce the prevalence pathogens on broiler meat. However, there are a limited number of studies comparing the effects of peracetic acid on broiler meat from different processing plants. The objective of this study was to determine the prevalence of Salmonella, Campylobacter, and spoilage microbes on broiler meat at different stages of poultry processing in commercial plants that use peracetic acid as the primary antimicrobial. Results indicated that there was a high initial microbial presence on broiler meat at initial stages of processing in all three plants. Peracetic acid effectively reduced the prevalence and microbial load of all microbes analyzed in this study. All microbes were reduced to nondetectable levels in the finishing chiller. However, contamination of all microbes in mechanically deboned meat closely resembled initial carcass contamination. In conclusion, the intervention with the greatest effect on microbial prevalence was peracetic acid in carcass chilling tanks, and, given the level of contamination in mechanically deboned meat, an intervention at this step would be worth investigating.

Sampling in onarm production environments presents challenges that must be considered when doing hazard analysis. The sensitivity and specificity of the test used and the sample types chosen will have an impact on the food safety outcome and food safety decisions made during the interpretation of results. In this work, broiler houses were sampled for the presence of Salmonella spp. using two different sampling strategies and four different microbiological isolation procedures. The study was undertaken after complications arose during a field study evaluating the role darkling beetles play in the transmission of foodborne pathogens. It was determined that, based on this work, incorporating a secondary enrichment procedure into the isolation protocol significantly increased the isolation rate from the various sample types, including drag swabs and litter samples. It was also determined that when attempting to characterize the Salmonella-status of a particular broiler house, no one sampling strategy is superior. The results of this study demonstrate that both drag swabs and litter samples need to be utilized to accurately determine if the pathogen is present in a flock. Not only did the secondary enrichment procedure have a higher isolation frequency than the other three methods compared, it also highlighted the discrepancies of the other methods. Two commonly used isolation procedures, tetrathionate and Rappaport-Vassiliadis, were found to disagree on a significant number of samples analyzed. While the isolation frequencies for these procedures were not found to be statistically different, the analysis for agreement, kappa, did indicate that the procedures did not identify the same samples as positive. Overall, the secondary enrichment procedure identified all the samples positive that were also found to be positive by either of the other methods used. Since the secondary enrichment method is a modified version of the traditional delayed secondary enrichment procedure, which requires five additional day of incubation, this study also compared these two procedures. It was determined that the secondary enrichment protocol was as effective for isolating Salmonella from broiler house samples as the delayed secondary enrichment procedure. The secondary enrichment procedure, did however, provide for a quicker turn around for results.

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