2.2.1. Benefit of LAB: Safety, Adjuvant and Prevention of S. pneumoniae
LAB are a group of Gram-positive bacteria that produce a common end product—lactic acid—from the fermentation of sugars . These non-sporulating bacteria include species of Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus . Due to limited biosynthetic abilities for pre-formed amino acids, B vitamins, purine and pyrimidine, their habitats are restricted to the place, such as intestine, where the required compounds are abundant . They have positive effects on human and animal health and were widely used for food without causing any known health problem for thousands of years. This status is considered GRAS (generally recognized as safe).
LAB can be used as adjuvants for their immunostimulatory properties . This GRAS status of LAB in adults and infants and their abilities to stimulate immune responses make them very attractive candidates for the development of mucosal vaccines . Most LAB induce Th1 type responses, some LAB can induce different arms of the immune response , like L. reuteri induces Th2 responses and L. rhamnosus induces Th17 responses . Lactobacillus and Lactococcus are the main vaccine vehicles to delivery heterologous proteins or DNA to mucosal tissues