Zhaohao Shi

Current aspects of Salmonella contamination in the US poultry production chain and the potential application of risk strategies in understanding emerging hazards.

Abstract One of the leading causes of foodborne illness in poultry products is Salmonella enterica. Salmonella hazards in poultry may be estimated and possible control methods modeled and evaluated through the use of quantitative microbiological risk assessment (QMRA) models and tools. From farm to table, there are many possible routes of Salmonella dissemination and contamination in poultry. From the time chicks are hatched through growth, transportation, processing, storage, preparation, and finally consumption, the product could be contaminated through exposure to different materials and sources. Examination of each step of the process is necessary as well as an examination of the overall picture to create effective countermeasures against contamination and prevent disease. QMRA simulation models can use either point estimates or probability distributions to examine variables such as Salmonella concentrations at retail or at any given point of processing to gain insight on the chance of illness due to Salmonella ingestion. For modeling Salmonella risk in poultry, it is important to look at variables such as Salmonella transfer and cross contamination during processing. QMRA results may be useful for the identification and control of critical sources of Salmonella contamination.

The Potential Link between Thermal Resistance and Virulence in Salmonella: A Review

In some animals, the typical body temperature can be higher than humans, for example, 42°C in poultry and 40°C in rabbits which can be a potential thermal stress challenge for pathogens. Even in animals with lower body temperatures, when infection occurs, the immune system may increase body temperature to reduce the chance of survival for pathogens. However, some pathogens can still easily overcome higher body temperatures and/or rise in body temperatures through expression of stress response mechanisms. Salmonella is the causative agent of one of the most prevalent foodborne illnesses, salmonellosis, and can readily survive over a wide range of temperatures due to the efficient expression of the heat (thermal) stress response. Therefore, thermal resistance mechanisms can provide cross protection against other stresses including the non-specific host defenses found within the human body thus increasing pathogenic potential. Understanding the molecular mechanisms associated with thermal responses in Salmonella is crucial in designing and developing more effective or new treatments for reducing and eliminating infection caused by Salmonella that have survived heat stress. In this review, Salmonella thermal resistance is assessed followed by an overview of the thermal stress responses with a focus on gene regulation by sigma factors, heat shock proteins, along with the corresponding thermosensors and their association with virulence expression including a focus on a potential link between heat resistance and potential for infection.

Comparison of methods for quantitating Salmonella enterica Typhimurium and Heidelberg strain attachment to reusable plastic shipping container coupons and preliminary assessment of sanitizer efficacy

ABSTRACT Salmonella serovars, one of the leading contributors to foodborne illness and are especially problematic for foods that are not cooked before consumption, such as fresh produce. The shipping containers that are used to transport and store fresh produce may play a role in cross contamination and subsequent illnesses. However, methods for quantitatively attached cells are somewhat variable. The overall goal of this study was to compare conventional plating with molecular methods for quantitating attached representative strains for Salmonella Typhimurium and Heidelberg on reusable plastic containers (RPC) coupons, respectively. We attached Salmonella enterica serovar Typhimurium ATCC 14028 and serovar Heidelberg SL486 (parent and an antibiotic resistant marker strain) to plastic coupons (2.54 cm2) derived from previously used shipping containers by growing for 72 h in tryptic soy broth. The impact of the concentration of sanitizer on log reductions between unsanitized and sanitized coupons was evaluated by exposing attached S. Typhimurium cells to 200 ppm and 200,000 ppm sodium hypochlorite (NaClO). Differences in sanitizer effectiveness between serovars were also evaluated with attached S. Typhimurium compared to attached S. Heidelberg populations after being exposed to 200 ppm peracetic acid (PAA). Treatment with NaClO caused an average of 2.73 ± 0.23 log CFU of S. Typhimurium per coupon removed with treatment at 200 ppm while 3.36 ± 0.54 log CFU were removed at 200,000 ppm. Treatment with PAA caused an average of 2.62 ± 0.15 log CFU removed for S. Typhimurium and 1.41 ± 0.17 log CFU for S. Heidelberg (parent) and 1.61 ± 0.08 log CFU (marker). Lastly, scanning electron microscopy (SEM) was used to visualize cell attachment and coupon surface topography. SEM images showed that remaining attached cell populations were visible even after sanitizer application. Conventional plating and qPCR yielded similar levels of enumerated bacterial populations indicating a high concordance between the two methods. Therefore, qPCR could be used for the rapid quantification of Salmonella attached on RPC.

Overview of Salmonellosis and Food-borne Salmonella : Historical and Current Perspectives

Abstract Salmonella continues to be one of the more major food-borne pathogens from a public health standpoint. Historically pathogenic Salmonella have probably always been associated with human disease but the linkage between the pathogen and salmonellosis has not always been obvious and is more of a recent development. As epidemiology and identification methodologies became more sophisticated, the cause and effect between human clinical salmonellosis and water and food sources was established and appropriate control measures identified. However, food-borne salmonellosis continues to be problematic in part due to the biology of Salmonella and its occurrence in a wide array of environmental niches as well as the ability of some serovars to occupy the gastrointestinal tract of multiple host animals. In particular, food commodities including poultry and eggs continue to be prominent sources of food-borne salmonellosis. In this chapter, an overview of the historical milestones of Salmonellas initial identification as a pathogen causing human systemic disease, and later as a food-borne pathogen, will be discussed. Current patterns and trends of Salmonella occurrence worldwide will be described followed by an introduction to the presence of food-borne Salmonella in poultry and egg production.Salmonella continues to be one of the more major food-borne pathogens from a public health standpoint. Historically pathogenic Salmonella have probably always been associated with human disease but the linkage between the pathogen and salmonellosis has not always been obvious and is more of a recent development. As epidemiology and identification methodologies became more sophisticated, the cause and effect between human clinical salmonellosis and water and food sources was established and appropriate control measures identified. However, food-borne salmonellosis continues to be problematic in part due to the biology of Salmonella and its occurrence in a wide array of environmental niches as well as the ability of some serovars to occupy the gastrointestinal tract of multiple host animals. In particular, food commodities including poultry and eggs continue to be prominent sources of food-borne salmonellosis. In this chapter, an overview of the historical milestones of Salmonellas initial identification as a pathogen causing human systemic disease, and later as a food-borne pathogen, will be discussed. Current patterns and trends of Salmonella occurrence worldwide will be described followed by an introduction to the presence of food-borne Salmonella in poultry and egg production.

Draft Genome Sequences of Salmonella enterica Serovar Enteritidis and Kentucky Isolates from Retail Poultry Sources

ABSTRACT The draft genome sequences of four Salmonella enterica serovar Enteritidis and Kentucky isolates were evaluated for biofilm formation and antibiotic resistance. The Salmonella serovar Kentucky strains CFS84 and CFS85 and Salmonella serovar Enteritidis strains CFS86 and CFS87 were isolated from retail poultry sources in Arkansas.

Chapter 9 – Foodborne Salmonella in Laying Hens and Egg Production

Abstract Salmonella spp. remain an ongoing source of foodborne diseases. Numerous food products can serve as sources of this pathogen, including fresh produce, red meats, poultry, and egg products. With egg production, exposure to Salmonella can occur at any stage from the laying hen to egg processing. Salmonella Enteritidis has been the primary serovar of concern in egg contamination and considerable research has focused on understanding the relationship between this serovar and egg production. As more has become known, the interaction between the laying hen and infection by S. Enteritidis has been established. As a result, more effective control measures for limiting S. Enteritidis colonization of the laying hen and limiting egg contamination have been developed. However, more work needs to be conducted on the gastrointestinal ecology of S. Enteritidis and its relationship with the indigenous microbial population.

Chapter 19 – Unraveling Food Production Microbiomes: Concepts and Future Directions

Abstract Characterization of the microbiota in food production systems both in the live animal and in postharvest food–processing settings has always been a part of the analytical landscape. Certainly, foodborne pathogen detection has been important from a public health standpoint and continues to offer challenges for development of control measures to limit the impact of the presence of foodborne pathogens in all phases of food production from farm to fork. With the advent of improvements and subsequent widescale application of 16S ribosomal RNA gene–based microbiome sequencing, a new appreciation of microbial community dynamics is becoming realized. The interaction between the gastrointestinal tract microbiome and the host animal has helped to establish the concept of a healthy gut and identification of factors that may negatively influence the gut ecosystem is just one such example. However, as the data sets expand at a rapid rate and become multidimensional, the computational bioinformatics can become a limitation. There are several software pipelines currently available that are relatively accessible. In the future, computer program tools such as machine learning may provide further insight into microbiome data and potentially be used for making predictions based on data availability. Such approaches could be useful for the food industry to appraise various intervention strategies implemented in food production.Characterization of the microbiota in food production systems both in the live animal and in postharvest food–processing settings has always been a part of the analytical landscape. Certainly, foodborne pathogen detection has been important from a public health standpoint and continues to offer challenges for development of control measures to limit the impact of the presence of foodborne pathogens in all phases of food production from farm to fork. With the advent of improvements and subsequent widescale application of 16S ribosomal RNA gene–based microbiome sequencing, a new appreciation of microbial community dynamics is becoming realized. The interaction between the gastrointestinal tract microbiome and the host animal has helped to establish the concept of a healthy gut and identification of factors that may negatively influence the gut ecosystem is just one such example. However, as the data sets expand at a rapid rate and become multidimensional, the computational bioinformatics can become a limitation. There are several software pipelines currently available that are relatively accessible. In the future, computer program tools such as machine learning may provide further insight into microbiome data and potentially be used for making predictions based on data availability. Such approaches could be useful for the food industry to appraise various intervention strategies implemented in food production.

Quantification of nitrogen in the liquid fraction and in vitro assessment of lysine bioavailability in the solid fraction of soybean meal hydrolysates

ABSTRACT Soybean meal (SBM) is a product generated from the manufacture of soybean oil and has the potential for use as a source of fermentable sugars for ethanol production or as a protein source for animal feeds. Knowing the levels of nitrogen available from ammonium is a necessary element of the ethanolic fermentation process while identifying the levels of essential amino acids such as lysine is important in determining usage as a feed source. As such the purpose of this study was to quantify total nitrogen and ammonium in the liquid fraction of hydrolyzed SBM and to evaluate total and bioavailable lysine in the solid fraction of the hydrolyzed SBM. The effects of acid concentration, cellulase and β-glucosidase on total and ammonium nitrogen were studied with analysis indicating that higher acid concentrations increased nitrogen compounds with ammonium concentrations ranging from 0.20 to 1.24 g L−1 while enzymatic treatments did not significantly increase nitrogen levels. Total and bioavailable lysine was quantified by use of an auxotrophic gfpmut3 E.coli whole-cell bioassay organism incapable of lysine biosynthesis. Acid and enzymatic treatments were applied with lysine bioavailability increasing from a base of 82% for untreated SBM to up to 97%. Our results demonstrated that SBM has the potential to serve in ethanolic fermentation and as an optimal source essential amino acid lysine.

Salmonella and the Potential Role for Methods to Develop Microbial Process Indicators on Chicken Carcasses

Foodborne salmonellosis originating from poultry products is a major problem, and post harvest control is important to prevent Salmonella contamination. However, assessing when and where Salmonella contamination occurs, and, more importantly, which routes of contamination have the greatest impact on introduction and dissemination in the final poultry meat product is an extremely complex question with a tremendous number of variables. Estimating Salmonella prevalence in poultry processing and the significance/role of Salmonella prevalence in finished products is a critical aspect of food safety control, with USDA regulations updating regularly to improve food safety. Numerous cultural methodologies exist for the detection of Salmonella . However, it is also critical to establish non- Salmonella bacteria and indicator organism profiles that allow for a more continuous monitoring or oversight of microbial shifts that potentially could occur during processing. Development of quantitative risk assessment models, for assessing where the greatest risks for contamination occur, may also allow for prioritizing optimal intervention strategies to achieve the most effective reductions in Salmonella contamination of poultry products.