With concerns in the use of antibiotic growth promoters in poultry agriculture, alternative strategies that ensure sustainability of the industry in producing safe poultry meat and eggs are important. Among the food-borne pathogens transmitted through poultry products, Salmonella poses a significant health hazard, with contaminated eggs serving as a major vehicle of the pathogen in causing human infections. Egg-laying chickens serve as an important reservoir of Salmonella, where it can colonize various parts of the intestinal tract and other vital organs, thereby underscoring the need for controlling the bacterium in birds. Plant-derived compounds (PDCs), an emerging class of natural and environmentally friendly antimicrobials have been investigated for their antimicrobial benefits in animal-derived foods, including eggs. However, their use as feed supplements in live chickens for controlling pathogens and improving gut health has gained momentum only recently. This chapter focuses on the potential use of PDCs in layer chickens for improving preharvest food safety. Scientific data on existing, new, and/or emerging PDCs that have potential use in layers for controlling Salmonella are discussed along with their classification, sources, and possible mechanisms of action. A discussion of in vivo studies on the effects of PDCs on layer performance, intestinal health, and gut microbiome is also included. In addition, challenges in experimental research involving PDCs and factors affecting the applicability of PDCs in commercial layer diets, including economic viability and palatability issues, with suggested mitigation methods are presented.

Food-borne Salmonella continues to be a public health issue both from an illness standpoint as well as economically. Poultry and eggs represent a primary source of food-borne Salmonella with several serovars usually being the primary isolates specifically identified as originating from these food product sources. Salmonella Heidelberg has emerged as a serovar of increasing prominence, particularly in some of the more recent egg-associated outbreaks. In this chapter the incidence of S. Heidelberg in poultry and eggs as well as characteristics and ability to cause disease as a food-borne pathogen are discussed. Particular issues such as virulence capabilities and antimicrobial resistance are also described. Finally, the adaptability of S. Heidelberg and implications are summarized.

The strategy for the detection of Salmonella Enteritidis in layer hen flocks has changed over the last 25years. Serology did not effectively provide the answers, so the focus went to culturing birds and eggs. Neither was feasible as a screening test; however, each one serves as a means of confirming positive flocks. It was determined that the environment of the house would be the means of detection. Because of the organic and bacterial loads on these samples, the isolation methods had to be optimized. This led to improvements in the enrichment and plating media. The focus now has turned to molecular methods of detection. These still require enrichment of the sample and subsequent culture of the positives for confirmation. As the molecular methods become widely used and confidence in their results develops over time, culture confirmation will not be as important. With serotype-specific or multiplex polymerase chain reaction systems, companies can receive information on not only the presence or absence of Salmonella, but also whether specific serotypes are present.

The intestinal microbial ecosystem of poultry is a dense and diverse population that can be utilized to improve production efficiency and enhance the safety of food. Strategies that harness this complex natural resource have been developed that improve production efficiency, animal health, and food safety on the farm. Products used in laying hens to increase the efficiency of egg production and safety of the food supply include: probiotics (DFM) and competitive exclusion (CE) cultures depending on the age of the hen and production goals. The efficacy (or lack thereof) of each approach or individual product is due to specific microbial ecological factors within the layer gut and its native microbiome, as well as external environmental factors that alter the competitive pressures of the gut. This review explores the efficacy of these products in improving production efficiency, gut architecture, skeletal fitness, the immune system, as well as the safety of eggs and egg production.

Salmonella enterica subsp. enterica comprises more than 2500 separate serovars that differ genetically and in their pathogenicity. From the point of view of infection biology they may be divided into two groups or pathovars.

Egg production in Canada is highly controlled under a supply management system, and all registered egg producers must conduct regular testing of the production facilities for Salmonella. In most provinces, the testing is conducted under the guidelines of the “Start Clean-Stay Clean” on-farm food safety programs. This Hazard Analysis Critical Control Point-based program incorporates on-farm activities that help to reduce the risk of Salmonella Enteritidis contamination of eggs, thus reducing the risk of human illness. Although human illnesses associated with Salmonella enterica serovar Enteritidis have increased in Canada, there is little evidence to link the increase to consumption of eggs produced through the supply management system, as many other risk factors for Salmonella Enteritidis infections have been identified. However, safe food handling practices throughout the food chain need to be improved to mitigate infections from handling or consumption of eggs.

The Korean layer industry grew significantly over the last two decades in response to an increase in the per capita consumption of eggs. Korea has utilized intensive livestock operation systems due to its limited land space, making poultry vulnerable to fowl diseases. Eggs are produced under regulations such as the Hazard Analysis Critical Control Point system or Egg Grading System and eggs from farms are tested annually to detect Salmonella enterica serovar Enteritidis (MIFAFF Notice, 2009-169). Although eggs and egg products have been implicated in outbreaks of human salmonellosis in South Korea, Salmonella was not prevalent among shell eggs in previous studies. However, previous results may be attributed to the difficulty of making confident risk assessments regarding Salmonella contamination in eggs and egg products in Korea. A national survey to obtain reliable data on the distribution of Salmonella contamination among eggs and egg products is strongly recommended as a preventive measure for egg safety.

Laying hens can become infected with a number of non–host-specific Salmonella serovars, of which Salmonella Enteritidis and Salmonella Typhimurium (including monophasic strains) are considered the most relevant threat to public health in Europe. S. Enteritidis in particular is able to persist indefinitely on layer farms unless effective interventions are implemented. In 2014, 2.5% of adult laying flocks in the European Union were reported to be infected by Salmonella (0.9% with either S. Enteritidis or S. Typhimurium). Laying hens can become infected as a result of contact with a contaminated environment (either at the hatchery or farm). Once Salmonella infection is established in a flock, it is perpetuated through a fecal–oral cycle. Rodents, particularly house mice, play a major role in the persistence of the infection, especially for flocks infected with S. Enteritidis. Rodents can readily become infected via contact with feces and dust and harbor salmonellae in their intestines and liver, where they can multiply to high numbers and persist for the whole life of a wild mouse. Contamination of feeding and water supply systems and surfaces of buildings and equipment by rodent droppings leads to infection in birds and contamination of egg collection equipment can directly contaminate eggs. Even when hens are vaccinated against Salmonella, the presence of breeding and young rodents shedding high numbers of organisms usually undermines vaccinal protection, although the occurrence of systemic infection of hens and internally contaminated eggs will still be reduced. When infected flocks are removed at the end of a production cycle, Salmonella can persist in the environment and infect replacement flocks. Intensive baiting of rodents before depopulation, and especially at the time when houses are empty and poultry feed has been removed, is essential to break the cycle of infection and avoid Salmonella carryover between flocks. Flies and litter beetles can also be infected for short periods and may be involved in the transmission and persistence of infection when downtime between flocks is short, or multiple age production is in place on the laying farm. Infestation by red mites can reduce the ability of birds to resist or clear infection, as a result of stress and anemia, and red mites are the main means of transmission of the nonzoonotic Salmonella Gallinarum biovar Gallinarum infection. Salmonella can survive for months in contaminated dust and laying hen houses tend to generate large quantities of dust during the long production cycle. Effective cleaning and disinfection between flocks is often costly to implement in laying houses, especially large cage units that are usually not designed to facilitate drainage after washing, leading to persistence of contamination between flocks. Removing all organic matter and using highly bioactive disinfectants such as aldehydes at the correct concentration and application rate is essential to avoid environmental persistence of Salmonella. Salmonella can be present at low prevalence in adult laying hens in mid lay and in older pullets and may therefore be difficult to detect. It is often assumed that new infections have entered laying farms when in reality the Salmonella has been continuously present but below the limits of detection of standard monitoring programs. Effective sampling and testing is therefore essential to the control of Salmonella on-farm. In the European Union, major progress on control of Salmonella in egg production has only been achieved after the introduction of effective vaccination programs and the application of severe financial penalties in terms of trade restrictions on the sale of fresh eggs from infected farms, which in many countries makes continued production from infected flocks economically unsustainable. Official sampling by the competent authority is also in place to validate operator sampling. Such incentives are usually required to ensure that effective control measures that come at a cost to the producer are fully implemented.

The growth of the poultry industry in South America has been explosive in recent years. More than 238 million layers are located in South America producing more than 4million tons of eggs. Brazil, Argentina, and Colombia are the most important egg producers in this region. Nonenriched cage systems are not prohibited in South America and most of the laying hens are located in battery cage farms, which include automatic and conventional (manual) battery cage systems. Salmonella Gallinarum and Salmonella Enteritidis are the most prevalent serotypes in layer farms. South American countries have different regulations to control Salmonella in their flocks through various National Poultry Improvement Plans. This control is focused on S. Gallinarum biovars Gallinarum and Pullorum, S. Enteritidis, S. Typhimurium, and S. Heidelberg. Inactivated (killed) and attenuated (live) vaccines are available to control Salmonella spp. in poultry in South America, but there are some differences in licensed vaccines.

Eggs constitute a vital part of the human diet globally. Due to increasing concerns of food-borne outbreaks caused by consumption of contaminated egg and egg products, controlling egg-borne pathogens at the farm level and during processing is warranted. Postharvest treatment of eggs is essential to minimize product contamination from poultry house and processing plants, and reduce residual antibiotics, disinfectants, or synthetic chemicals on eggs. The common practices to enhance egg safety include effective eggshell decontamination by wash/spray and storage at refrigeration to prevent growth of food-borne pathogens, especially Salmonella. Despite the aforementioned practices, egg and egg products contaminated with Salmonella have been frequently implicated in outbreaks worldwide. Thus there is an interest to identify novel strategies for improving postharvest egg safety, especially those involving natural and environment friendly approaches. Extensive research in the last few decades has identified many plant- and animal-derived natural molecules exhibiting antimicrobial properties against an array of food-borne pathogens. This chapter discusses the efficacy of various traditional and natural approaches, including phytochemicals, organic compounds, probiotics, and bacteriophages in improving the microbiological safety of eggs.