[Lactococcus lactis: an opportunistic bacterium?]

Lactic bacteria have been used for centuries to ferment food and thus, to better preserve them. Considered as inoffensive for man, its use has largely spread in food industry. Some species are even being considered for the treatment of human diseases. Indeed, the development of new cellular biology technologies opens opportunities for the use of these bacteria as biotherapeutic agents. These species would produce heterogeneous proteins such as enzymes (lipase, lactase, esterase), chemical mediators (hormones and interleukins), and molecules able to stimulate local immune responses. However, rare cases of human infection, sometimes severe, were reported recently. They generally occured in patients with comorbidities with consumption of unpasteurized dairy products reported for some. The scarcity of these cases and their favorable outcome should not hinder the industrial and medical use of these bacteria.