This species is a non-sporing, rod-shaped, gram positive microorganism that can be found within the reproductive and digestive tract of the human body.

To solve this discrapency, Dellaglio et al. argued to simply replace the type with ATCC 334, which is closer to these "other strains", and to bury the name "L. paracasei".

[2] As of December 2023, the accepted taxonomy under the species complex is as follows:[7][8] The most common application of L. casei is industrial, specifically for dairy production.

[14] Additionally, trials have shown significantly shorter recovery times in children suffering from acute diarrhea (primarily caused by rotavirus) when given different L. casei treatments when compared to placebo.

[16] In the preparation of food, L. casei bacteria can be used in the natural fermentation of beans to lower levels of the compounds causing flatulence upon digestion.

[20] In the past few years, many studies have been conducted in the decolorization of azo dyes by lactic acid bacteria such as L. casei TISTR 1500, L. paracasei, Oenococcus oeni, etc.

[22][23][24] Lactic acid bacteria (LAB) is widely exploited for its probiotic and fermenting properties, so understanding how its genetic material is exchanged was crucial for researchers.

A wide variety of comparative analyses were used to determine that horizontal gene transfer (HGT) influenced the evolution of the Lactobacillus genus.

[26] Within LAB, they are responsible for metabolizing different molecules, hydrolyzing proteins, resisting antibiotics, DNA, and phages, and modifying genetic elements.

[citation needed] Finally, transduction in Lactobacillus cells is a bacteriophage-mediated transfer of plasmid or chromosomal genetic information.