Probiotics are viable bacteria that beneficially influence the
health of the host (1, 2). Probiotic bacteria selected for commercial
use in foods and in therapeutics must retain the characteristics
for which they were originally selected (1–3). These
include characteristics for growth and survival during manufacture
and, after consumption, during transit through the stomach
and small intestine. Importantly, probiotics must retain the
characteristics that give rise to their health effects. Consequently,
it is necessary to test the stability of these characteristics
during manufacture and storage and to ensure that they are
retained in different types of foods (3, 4). The initial screening
and selection of probiotics includes testing of the following
important criteria: phenotype and genotype stability, including
plasmid stability; carbohydrate and protein utilization patterns;
acid and bile tolerance and survival and growth; bile metabolism;
intestinal epithelial adhesion properties; production of
antimicrobial substances; antibiotic resistance patterns; ability to inhibit known gut pathogens, spoilage organisms, or both;
and immunogenicity.