Prebiotics are dietary components that the host microbiota can selectively ferment, changing the composition in a way that is helpful. Prebiotics typically consist of fiber-rich substances of various chemical compositions, such as fructo-oligosaccharides (FOS), which have been shown to selectively increase lactobacilli and bifidobacteria populations while lowering the colonization of Salmonella spp. and other pathogenic microbes in the guts of chickens and pigs. The performance of the animal itself is consistently enhanced by the use of probiotic strains, in which live bacteria help the host. It has been demonstrated that particular strains of the bacteria Bacillus and Lactobacillus spp. improve the general health of pigs exposed to Salmonella and lower the number of Campylobacter infections in poultry. During pet food processing, both these prebiotic and probiotic dietary components are used to balance out the diet of the animals.