[Vaccine development: strategies for coping with the antigenic diversity of bacteria]

Bacterial pathogens have evolved a whole range of anti-immune strategies to overcome both the innate and acquired immunity of their hosts. These strategies play a crucial role in the capacity of pathogens to trigger disease and also explain why it is so difficult to develop vaccines and to control these microorganisms. One of the main problems is that bacteria are highly antigenically diverse. The vaccination strategies for coping with this variability, which we are starting to understand more fully as a result of sequencing bacterial genomes, consist of using either several variants of one or more proteins capable of inducing protective antibodies, or else proteins (or protein fragments) or epitopes that have been relatively well preserved notably because they are involved in the pathogen's metabolism. The most sophisticated approach calls upon 'pan genomic' inverse vaccinology which compares the protein profiles of a large number of isolates from various strains of a single species in order to reveal the surface-expressed proteins present in all the isolates. Of these proteins, the ones which are expressed when the host is infected are then evaluated in order to determine their capacity to induce a protective immune response. So far this approach has been successful in controlling bacteria in humans and the way is now open for its application in veterinary medicine, thanks to progress with the genomic sequencing of pathogens of veterinary importance.