Under healthy breeding conditions, an egg's contents are generally sterile just after laying. However, they can be contaminated by a diversified microbiota containing food spoilage microorganisms and sometimes pathogenic bacteria. Eggs can be contaminated both externally, on the eggshell, and internally, i.e. during development. The egg may therefore be a vector of bacteria causing foodborne illness in humans: this is particularly the case for Salmonella.