Feed components have low water activity, making bacterial survival difficult, according to Ana Andino of the University of Tennessee. The mechanisms of Salmonella survival in feed and subsequent colonisation of poultry are unknown.

In a paper in Poultry Science, she and colleagues in Knoxville report their research comparing the ability of Salmonella serovars and strains to survive in broiler feed and to evaluate molecular mechanisms associated with survival and colonisation by measuring the expression of genes associated with colonization (hilA, invA) and survival via fatty acid synthesis (cfa, fabA, fabB, fabD).

Their data indicate the ability of strains to survive over time in poultry feed was strain-dependent and that up-regulation of cyclopropane fatty acid synthesis and down-regulation of virulence genes were associated with a response to the stress of desiccation .

The researchers inoculated feed with one of 15 strains of Salmonella enterica consisting of 11 serovars (Typhimurium, Enteriditis, Kentucky, Seftenburg, Heidelberg, Mbandanka, Newport, Bairely, Javiana, Montevideo and Infantis).

The largest reduction in Salmonella occurred at the first and third sampling time points (after four hours and four days) with the average reductions being 1.9 and 1.6 log colony forming units (cfu) per gramme, respectively.

For the remaining time points (eight and 24 hours and seven days), the average reduction was less than one log cfu per gramme - 0.6, 0.4 and 0.6, respectively.

Most strains up-regulated cfa (cyclopropane fatty acid synthesis) within eight hours, which would modify the fluidity of the cell wall to aid in survival, Andino and colleagues found.

They concluded that there was a weak negative correlation between survival and virulence gene expression indicating down-regulation to focus energy on other gene expression efforts such as survival-related genes.

Reference

Andino A., S. Pendleton, N. Zhang, W. Chen, F. Critzer and I. Hanning. 2014. Survival of Salmonella enterica in poultry feed is strain dependent. Poultry Science. 93(2):441-447. doi: 10.3382/ps.2013-03401