Use of vaccination in the eradication of strangles: the importance of differentiating infected from vaccinated animals (DIVA)

Abstract

of the library enabled the simultaneous identification of essential regions over 94% of the S. equi genome. A total of 253 genes were identified as required for growth in standard laboratory conditions, providing a blue-print for basic cell survival. Amongst other findings, the 14 genes associated with the iron-sequestering molecule equibactin, were all found to be non-essential to S. equi in vitro with the exception of the regulatory gene, eqbA. This gene mediates iron uptake to prevent intracellular iron toxicity, which is reflected by its importance in this study. To reduce the impact of phage infections, bacteria have developed ‘cell suicide’ abortive infection mechanisms. In S. equi, the genes encoding toxin production for abortive infection were found to be non-essential, but a gene encoding an anti-toxin was required. In a pilot study, a library of mutants was used to determine if TraDIS is able to identify genes involved in the interaction between S. equi and equine phagocytes (equine macrophage-like cells (eCAS)). Mutants containing insertions in 11 genes involved in resistance to oxidative stress and into two genes involved in capsule formation were reduced in fitness. The identification of these genes highlights the importance of maintaining both the capsule and the ability to resist oxidative stress in S. equi, in the presence of eCAS. The ability of TraDIS to simultaneously allocate importance to genes under particular conditions makes it an attractive high-throughput method with which to explore and build on current knowledge of the functional genomics of S. equi to direct the design of safer and more effective vaccines.