Explore the Human Microbiome [Interactive]

Mouth, Pharynx, Respiratory System

Many of the microbes that live in the body arrive first in the food we eat. At least 600 different species live in the mouth and throat, approximately 280 of which have been isolated and named. An imbalance of microorganisms within the mouth can lead to cavities, gum disease and the infection of root canals.

Streptococcus viridans

Three groups of closely related Streptococcus bacterial species that are found in the upper respiratory system and that do not cause illness unless they make it into the blood stream. Three groups of closely related Streptococcus bacterial species that are found in the upper respiratory system. S. viridans do not cause illness unless they make it into the blood stream.

Candida albicans

A species of fungus that can, if there is too much of it, cause thrush. But much less is known about the normal, low-level presence of this fungus in the mouth.

Neisseria sicca

Not to be confused with N. gonorrheae, which causes a sexually transmitted infection, N. sicca is normally found in the mucus of the upper respiratory tract.

Streptococcus salivarius

One of the bacterial groups that makes up the closely related Streptococcus viridans category and one of the first to colonize the oral cavity of newborns.

Stomach

Relatively few bacteria can survive in the acidic environment of the stomach for long periods of time.

Intestines

About 3.3 million genes are contained in the bacteria of the human gut, far outnumbering the estimated 20,000 to 25,000 genes that people inherit from their parents.

Helicobacter pylori

Normally thought of as a pathogenic bacterium because it can trigger the formation of gastrointestinal ulcers, H. pylori has also, more recently been implicated in the regulation of appetite.

Bacteroides fragilis

Research suggests that B. fragilis survives in the intestine by damping down the immune system’s inflammatory mechanisms.

Lactobacillus casei

An abundance of L. casei in the intestine in the first year of life has been linked to a lower incidence of asthma and allergy

Lactobacillus gasseri

Commensal bacteria have various effect on each other as well as on their hosts. L. gasseri appears to reduce the level of H. pylori in the body.

Escherichia coli

Among the most common bacteria found in the intestines of human beings. Most E. coli strains are harmless, but a few types of E. coli can cause severe diarrhea and even death.

Bacteroides thetaiotaomicron

A champion consumer of carbohydrates, B. thetaiotaomicron makes it possible for humans to digest the kind of fiber found in oat bran.

Lactobacillus reuteri

Found in a wide variety of vertebrates—from people to pigs, mice and some birds. Some strains of L. reuteri apparently specialize in certain hosts. For example, the L. reuteri in humans do not colonize germ-free mice very well.

Streptococcus thermophilus

A beneficial microbe that is used in the production of yogurt. S. thermophilus is particularly sensitive to the acidic environment of the stomach and may not survive to the intestine unless consumed in large amounts.

Urogenital tract

To date, more research has been conducted on the microbiome of the female as opposed to the male urogenital tract.

Urogenital tract

To date, more research has been conducted on the microbiome of the female as opposed to the male urogenital tract.

Corynebacterium aurimucosum

Commonly found in the vagina. Some variants of C. aurimucosum have been linked to an increased risk of miscarriage.

Ureaplasma parvum

Many women apparently harbor U. parvum colonies without showing any symptoms. However, these tiny bacteria can cause illness if they cross the mucus membranes of the urogenital tract and enter the bloodstream.

Skin

Among its many functions, the skin serves as a first line of defense against disease-causing micro-organisms. Different parts of the skin play host to different species of bacteria whose presence may make no difference to their host, be positively helpful or actually harmful—often depending on how well their immune system works and whether they suffer puncture wounds.

Pityrosporum ovale

A normal inhabitant of oily parts of the skin, also known as Malassezia, this yeast plays a role in the production of dandruff and the development of eczema—although it is not clear how since the presence of P. ovale by itself is not enough to cause a problem.

Corynebacterium jeikeium

One of several species that are common in moist sites on the skin.

Staphylococcus haemolyticus

Normally a benign resident of the skin, S. haemolyticus causes problems when it travels into the body on the surface of a catheter or other medical device. Like many other species in the human microbiome, this strain is also a common source of antibiotic resistance genes.

Trichosporon

A group of species of yeast that are normally benign but can lead to an unsightly infection of the hair shafts called white piedra.

Staphylococcus epidermidis

Perhaps the most common of the benign staphylococcus species on the skin, S. epidermidis can cause serious infections if it makes its way inside the body on the surface of a catheter or other medical device.

Stomach

Relatively few bacteria can survive in the acidic environment of the stomach for long periods of time.