Vertical transmission of Salmonella Reading
Recently, an unconventional serotype of Salmonella, S. enterica serotype Reading (S. Reading), emerged as a foodborne pathogen following a multistate outbreak in the US due to the consumption of contaminated turkey products. In response to this outbreak, the Centers for Disease Control (CDC) issued four recalls of turkey products, and the outbreak strain was found to be widespread at all levels of commercial turkey production, including live turkeys. However, no single supplier of raw turkey products or live turkeys was identified as accountable for the entire outbreak, and the CDC engaged the entire turkey industry to find solutions to end the public health event. Further studies on the outbreak strains revealed the emergence of a novel S. Reading turkey clonal group, plausibly vertically transmitted from breeders to progeny. Although vertical transmission of the novel S. Reading turkey clonal group from breeders to progeny was suspected, there was no direct evidence to prove it.
To develop appropriate intervention strategies, researchers from Mississippi State University evaluated the vertical transmission of the Salmonella Reading outbreak strain in turkeys using bioluminescent imaging.
In vitro and in vivo plasmid stability in the bioluminescent bacteria was over seven days. Further, the growth curves were similar between the parent and bioluminescent bacteria for both outbreak and non-outbreak strains. The stable bioluminescent S. Reading strains developed were used for live tracking in breeder hens. A total of 32 broiler breeder hens were intravaginally challenged with S. Reading outbreak and non-outbreak strains. A total of 70.5% (36/51) and 34.5% (19/55) of external egg surfaces tested positive for the outbreak and non-outbreak strains, respectively. A total of 4% (2/50) and 1.8% (1/55) of the internal egg contents tested positive for the outbreak and non-outbreak strains, respectively. To evaluate tissue colonization, 10 broiler breeder hens challenged with each strain were euthanized and ovary, oviduct and ceca samples were collected and analyzed on day seven post-challenge. At least 20% of ovaries, 70% of oviduct and 70% of ceca samples collected from the hens challenged with the outbreak and non-outbreak strains tested positive.
In conclusion, these findings clearly show the ability of the S. Reading to colonize reproductive tissues of breeder hens as well as vertically transfer to eggs. Also, this study shows that bioluminescent technology can be used in poultry for real time tracking and detecting the presence of bacteria.
