Lactobacillus as a Therapeutic Agent: A Comprehensive Clinical and Microbiological Review

Section 1: The Lactobacillus Genus: Foundational Biology and Evolving Taxonomy

This section establishes the fundamental biological identity of [Lactobacillus] and addresses the recent, significant shift in its taxonomy, a crucial framework for interpreting the scientific and clinical research discussed in this report.

1.1 Core Biological and Metabolic Characteristics

[Lactobacillus] is a genus of Gram-positive, rod-shaped, non-spore-forming bacteria belonging to the phylum Firmicutes.[1] They are typically catalase-negative, facultatively anaerobic or microaerophilic, meaning they can thrive in environments with little to no oxygen.[1] A key characteristic is their high tolerance for acidic conditions, which is fundamental to their role in fermented foods and their ability to survive transit through the low pH environment of the human stomach to reach the intestines.[3]

The defining feature of the genus is its metabolism of carbohydrates to produce lactic acid, making it the largest and most prominent group within the Lactic Acid Bacteria (LAB).[1] Based on their metabolic pathways and end-products, lactobacilli are traditionally divided into three functional groups [1]: