Bifidobacterium animalis lactis

*Bifidobacterium animalis* subspecies *lactis* (*B. animalis* subsp. *lactis*) is a subspecies of the bacterium *Bifidobacterium animalis*. It is a prokaryotic organism. It lives within the colons of mammals, and can be passed between animals. *Bifidobacterium animalis* subspecies *lactis* was initially named *Bifidobacterium lactis* when it was first found  in fermented milk in 1997. 

## Biology and ecology 
*Bifidobacterium animalis* subspecies *lactis* is a gram-positive, rod-shaped bacterium. It is non-motile (unable to move by itself). It is also unable to form spores, which are cells produced by bacteria to allow survival in extreme environmental conditions. *Bifidobacterium animalis* subspecies *lactis* lives within the guts of healthy adults and infants. Therefore, this bacterium is part of the gut microbiome, which is the collection of microorganisms living within the intestines. This bacterium can survive the harsh conditions within the gastrointestinal tract, which could be because the bacterium can produce exopolysaccharides. These are polysaccharides that are produced and transported out of the bacterium to protect it from the surrounding environment. *Bifidobacterium animalis* subspecies *lactis* is a lactic acid bacterium. This means lactic acid is formed as a product of carbohydrate fermentation, which is a process used by bacteria to generate energy.

## Health benefits 
*Bifidobacterium animalis* subspecies *lactis* is commonly used as a probiotic – this is a living microorganism that can be added to food or drink to improve the health of the person that consumes it. This bacterium is added to dairy products such as yoghurt, buttermilk, cottage cheese and other cheeses. It grows well in milk, which makes it suitable for adding to dairy products. Also, it is resistant to (can survive in) acid and has a high oxygen tolerance (can survive in the presence of oxygen), which allows the bacterium to survive when it travels through the gut after it has been consumed. 

Using *Bifidobacterium animalis* subspecies *lactis* as a probiotic can bring multiple health benefits. For example, the strain HN019 can treat constipation by increasing how often bowel movements occur. This strain can also strengthen the immune system by increasing the amounts of specific cells (T cells and natural killer cells) which are involved in the response to pathogens. The strain UABla-12 decreases the severity of symptoms and the abdominal pain of adults with irritable bowel syndrome (IBS) symptoms. The strain 420 be used for weight loss because it decreases the amount of fat around the waist and causes less food to be eaten. 

## Antibiotic resistance 
The strains of bacteria used as probiotics cannot have antibiotic resistance genes that could be passed on to other bacteria, like through horizontal gene transfer, as these genes could then be passed on to bacteria within the body. This would mean that harmful bacteria could not be killed using antibiotics, which is the usually how harmful bacteria are killed. Many strains of *Bifidobacterium animalis* subspecies *lactis* are resistant to the antibiotic tetracycline, and this is caused the presence of the *tet*(W) gene within these strains. There is no evidence of this gene being transferred between bacteria, therefore *Bifidobacterium animalis* subspecies *lactis* is safe for use as a probiotic. The ability of probiotic bacteria to transfer antibiotic resistance must be carefully monitored to ensure products containing these bacteria are safe for consumption. This is done by the Food and Drug Administration (FDA) in the United States and by the  European Food Safety Authority (EFSA) in the European Union.

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