Bacteria belonging to the genus Lactobacillus are members of the lactic acid bacteria (LAB), a broadly defined group characterized by the formation of lactic acid as the sole or main end product of carbohydrate metabolism. They can be found in plants or material of plant origin, silage, fermented food (yogurt, cheese, olives, pickles, salami, etc.), as well as in the oral cavities, gastrointestinal tracts (GIT), and vaginas of humans and animals (31). In particular, the Lactobacillus species found in the GIT have received tremendous attention due to their health-promoting properties. They are commonly used as probiotics, which are defined by the FAO/WHO as live microorganisms that when administered in adequate amounts confer a health benefit on the host.

The economic success and exciting prospects of probiotic products have accelerated research on intestinal lactobacilli. Genomics of Lactobacillus species is booming, and the genomes of five strains that belong to species commonly found in human fecal samples have recently been sequenced (50). Several comparative and functional genomic investigations have been conducted to gain information about the functionality of lactobacilli in the GIT (69). Unfortunately, a major misconception regarding the ecological role%2