**1. Introduction**

The genus *Lactobacillus* was discussed for the first time in 1901. These are rodshaped, nonspore-forming, Gram-positive bacteria found in fermented foods and are member of the gastro-intestinal tract and vaginal cavity of humans [1–4]. *Lactobacillus* is a group of bacteria with diverse species having higher GC content ranging from 32 to 53 mol% [3]. Morpho-microscopically *Lactobacilli* are rod shaped, non-motile and varying in length ranging from short to long. *Lactobacilli* are comprised a group of multifunctional microbes with shelf life extending characters of food as well as improving human health in the form of probiotics [4]. Studies of the whole bacterial genomic sequence enabled, the scientists to reclassify the species of *Lactobacilli* into 25 genera including an edited genus of *Lactobacillus* i.e. *Paralactobacillus* and *Lactobacillus delbrueckii* group and 23 other novel genera containing *Acetilactobacillus, Agrilactobacillus, Amylolactobacillus, Apilactobacillus, Bombilactobacillus,* 

*Companilactobacillus, Dellaglioa, Fructilactobacillus, Furfurilactobacillus, Holzapfelia, Lac ticaseibacillus, Lactiplantibacillus, Lapidilactobacillus, Latilactobacillus, Lentilactobacillus, Levilactobacillus, Ligilactobacillus, Limosilactobacillus, Liquorilactobacillus,* 

*Loigolactobacilus, Paucilactobacillus, Schleiferilactobacillus,* and *Secundilactobacillus* [5]. Overall, more than 250 species have been assigned to the genus *Lactobacillus previously and* are now referred to with a new genus name. *Lactobacillus* releases lactic acid as the major end product of metabolism during fermentation of glucose with small amounts of acetic and succinic acid [2, 3].

The most common habitat of *Lactobacilli* is the gastro-intestinal tract of mammals where these bacteria may colonize. This group of bacteria is also commonly found in mouth such as in tooth plaque, saliva, vaginal tract of humans and mammals [2, 3]. *Lactobacillus* species commonly isolated from GI tract are *Lactobacillus acidophilus, L. brevis, L. plantarum, Lactobacillus salivarius and Lactobacillus fermentum*. *Lactobacillus* are significantly required for gastrointestinal health and are not considered as a pathogen in healthy individuals except when having an association with dental caries [6, 7]. *Lactobacilli* are usually reflected as proactive microbes as they inhibit the growth of pathogenic microorganisms by producing lactic acid and other metabolic compounds [8]. While in immunocompromised patients' lactobacilli are intricate as pathogens and various reports of AIDS, organ transplant, neutropenia caused by *lactobacillus* infection has been published [9–11]. The most common infections caused by *Lactobacilli* are abscesses, bacteremia, endocarditis, neonatal meningitis, dental caries and chorioamnionitis [5, 12]. The chapter focuses on an exploration of the industrial potential of *Lactobacilli* for manufacturing a diversity of products. The purpose of this chapter is to gather literature related to the utilization of *Lactobacillus* species as a microbial candidate for commercial-scale production of valuable products for improving human and animal health by protecting them against pathogenic microflora. The major emphasis is to strive for the attention towards the sustainable application of potent *Lactobacillus* species for futuristic prosperities of mankind.
