Salmonellosis is a major public health concern worldwide, resulting in significant economic losses. In recent years, Salmonella enterica serotype Reading emerged as a major foodborne pathogen following a multistate outbreak in the United States through the consumption of contaminated turkey products. In response, the CDC issued four recalls of turkey products. However, no specific company was found accountable, and the entire U.S. turkey industry was engaged in the investigation.
Furthermore, a comprehensive genomic investigation revealed the emergence of a novel S. Reading turkey clonal group that is hypothesized to be vertically transmitted from breeders to progeny and resulted in this outbreak. This may indicate that S. Reading is widespread in the turkey industry, and pre-harvest control measures—such as testing and monitoring of breeder flocks and their progeny, as practiced for other vertically transmitted Salmonella serotypes like S. Enteritidis—might be needed to reduce the transmission of this serotype. However, there is currently no direct evidence of transmission of S. Reading from breeders to progeny.
Traditionally, to control and maintain low levels of Salmonella in turkey products, USDA FSIS approved chemical interventions are used in the turkey processing plants. However, pre-harvest interventions at the farm level are more cost-effective and allows for better elimination of the pathogen than excessive processing plant interventions. To develop appropriate intervention strategies, there is a critical need to understand the potential of vertical transmission of S. Reading from breeders to progeny through fertile hatching eggs.
Bioluminescence imaging is a highly sensitive, non-invasive, non-toxic technique that can be used for real-time quantification and tracking of live bacteria in hosts. Dr. Reshma Ramachandran’s research team from Mississippi State University has recently developed a bioluminescent S. Reading strain that can be effectively used for real-time tracking of the transmission of S. Reading in turkeys. In fact, this bioluminescence technology is a highly effective, non-invasive tool that can allow the viewing of the colonization of the bioluminescent bacteria in internal organs and track its transmission following live bird challenge. Also, this technique may provide quicker and more reliable results when compared to traditional culture-based methods and may significantly reduce the number of birds compared to traditional live bird challenge studies.
USPOULTRY and its Foundation have funded a project to identify the potential of bioluminescent S. Reading outbreak and non-outbreak strains to colonize the reproductive tissues and vertically transfer to the poults through fertile eggs. Commercial turkey laying breeder hens will be intravaginally challenged with the two bioluminescent strains (outbreak and non-outbreak). Eggs laid will be collected for 21 days, set for incubation, and hatched. To track vertical transmission of S. Reading, spleen, liver and gastrointestinal tract of day-old poults and reproductive organs of hens will be collected and visualized using an in vivo imaging system to confirm the presence of bioluminescence.
The findings from this study may allow for a greater understanding of the colonization and transmission of S. Reading and can assist the turkey industry in developing effective pre-harvest intervention strategies to control this pathogen. If the result of this study proves that S. Reading can be vertically transmitted, it will indicate that pre-harvest interventions should target not only the commercial turkey flocks but also the turkey breeders to reduce the transmission of this serotype. The differences between the outbreak and non-outbreak S. Reading strains in colonization and transmission in turkeys also will be identified. Further, this study may provide a novel approach to track the vertical transmission of pathogens in poultry.
Denise Heard, DVM, MAM, ACPV, is vice president, research programs at the U.S. Poultry & Egg Association.
