Propionibacterium is a genus of bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 named for their unique metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

: They are able to synthesize propionic acid

Propionic acid

Propanoic acid is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor...

 by using unusual transcarboxylase enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s.

Its members are primarily facultative parasites and commensals

Commensalism

In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...

 of human

Human

Humans are the only living species in the Homo genus...

s and other animals, living in and around the sweat gland

Sweat gland

Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...

s, sebaceous gland

Sebaceous gland

The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...

s, and other areas of the skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

. They are virtually ubiquitous and do not cause problems for most people, but propionobacteria have been implicated in acne

Acne

Acne is a general term used for acneiform eruptions. It is usually used as a synonym for acne vulgaris, but may also refer to:*Acne aestivalis*Acne conglobata*Acne cosmetica*Acne fulminans*Acne keloidalis nuchae*Acne mechanica...

 and other skin conditions.

The strain Propionibacterium freudenreichii

Propionibacterium freudenreichii

Propionibacterium freudenreichii is a Gram-positive, nonmotile bacterium that plays an important role in the creation of Emmental cheese, and to some extent, leerdammer. Its concentration in Swiss-type cheeses is higher than in any other cheese. Propionibacteria are commonly found in milk and dairy...

subsp. shermanii is used in cheesemaking to create CO₂ bubbles that become "eyes

Eyes (cheese)

Eyes are the round holes that are a characteristic feature of Swiss-type cheese and some Dutch-type cheeses. They are bubbles of carbon dioxide gas that is produced by bacteria in the cheese....

", round holes in the cheese.