Persistence of vaccine origin SalmonellaTyphimurium through the poultry production continuum, and development of a rapid typing scheme for their differentiation from wild type field isolates

Salmonellaenterica serovar Typhimurium is one of the top Salmonellaserovars annually linked to poultry production and corresponding human illnesses. Because of this, vaccination of commercial poultry against SalmonellaTyphimurium has been a focal point in recent years. There are several commercially available SalmonellaTyphimurium vaccines available for use in poultry production. Among these are modified live vaccines, including Poulvac ST (Zoetis), Megan Egg (AviPro), and Megan Vac 1 (AviPro). In this study, analyses of 27 field isolates of SalmonellaTyphimurium from poultry sources indicated evidence for the persistence of some vaccine-origin strains through the commercial production cycle. Further analyses of 26,812 database isolates indicated vaccine-origin isolates are persisting frequently through processing, are present on retail meat products, and are even occasionally found in human patients. A novel polymerase chain reaction (PCR) was created and validated which enables simultaneous identification of Salmonellaenterica sp., the SalmonellaTyphimurium serovar, and differentiation of wild type SalmonellaTyphimurium from live attenuated vaccines involving mutations in the cya/crpor aroAgenes. The PCR was developed considering whole genome differences between the vaccines and wild type field isolates and was validated using different field isolates and recovered vaccine strains. This method enables poultry producers to rapidly determine if recovered field isolates have a vaccine origin.