The dynamics of Salmonella infection in cattle and their peripheral lymph nodes

The overall goals and objectives of this research are to:

Objective 1 – Investigate Salmonella transmission paths to cattle lymph nodes and assess bacterial replication within these nodes. Determine if immune responses are initiated following Salmonella uptake by the nodes.

Objective 2 – Fine-tune experimental model of inoculation as a cost-effective method for testing of the effects of novel pre-harvest interventions with a minimal number of animals.

Investigators propose to create a reliable and quantitative method that can measure the impact of interventions designed to reduce the carriage of Salmonella in peripheral lymph nodes (PLN) of cattle. Investigators will determine, in unprecedented detail, the population dynamics of Salmonella colonization both during transit of the bacteria to the cattle lymph nodes and while resident in the PLN. If successful, the method will dramatically reduce the number of animals needed to test and optimize novel intervention strategies to prevent PLN colonizations.

Investigators will combine two powerful techniques that they have pioneered. First, the transdermal route of Salmonella delivery into cattle is well tolerated by calves and results in consistent recovery of bacteria from the nearest peripheral lymph nodes. Second, they will use novel pools of hundreds of different Salmonella lineages, each individually tagged at a neutral genome location. Each unique pool of marked bacteria can be separately traced after inoculation in different locations in the cattle body. The number of bacteria that reach the lymph node and their amount of cell division can be determined precisely. Using this combination of novel tools, investigators will be able to observe and measure exactly how Salmonella spreads over time and across organs from various inoculation sites in individual animals. It will also be determined if a first inoculation leads to an immune response, by measuring the success of a second inoculation with a different pool of the same bacterial strain three weeks later. This represents the first step in validating whole-cell vaccines as interventions. Funded in part by The Beef Checkoff