Bifidobacterium lactis is also known as Bifidobacterium animalis subsp. lactis;

They are typically gram-positive, anaerobic, rod-shaped bacterium which can be found in the large intestines of most mammals, including humans.

Bifidobacterium lactis is the species of Bifidobacterium most commonly used in food products, as it is more robust than other species of Bifidobacterium genus. Amongst other characteristics, B. animalis subsp. lactis exhibits elevated oxygen tolerance, enabling it to survive in a wider range of environments. This probiotic species has also been shown to inhibit the toxic effects induced by the wheat protein gliadin, a component of wheat gluten. Wheat intolerance is becoming far more prevalent in modern society, but wheat products are staple foods in many cultures, so the potential of this bacterial species to help minimise some of the negative side effects of gluten consumption is attracting some interest.

References:

Maneerat, S., Lehtinen, M., Childs, C., Forssten, S., Alhoniemi, E., Tiphaine, M., . . . Rastall, R. (2013). Consumption of Bifidobacterium lactis Bi-07 by healthy elderly adults enhances phagocytic activity of monocytes and granulocytes. Journal of Nutritional Science, 2, E44. doi:10.1017/jns.2013.31 [L]