But biochemically, archaea are as different from bacteria as they are from us. Most archaea also have a cell wall, but theirs is very different from the peptidoglycan cell wall of bacteria.
Archaea are best known for living in extreme environments , but they also live in non-extreme environments, including the human gut and skin. Fungi are single-celled or multicellular organisms with nuclei and with cell walls made of chitin. They also have membrane-wrapped organelles, including mitochondria. Unlike plants, fungi cannot make their own food. Familiar fungi include yeasts, molds, and mushrooms. Yeasts live as small, individual cells, between the size of bacteria and our own cells.
Molds and mushrooms are actually the fruiting bodies of fungi that live as long, microscopic fibers. Fungi are important decomposers in most ecosystems. Their long, fibrous cells can penetrate plants and animals, breaking them down and extracing nutrients. Several species of fungi, mostly yeasts, live harmlessly on the human body.
Protists are single-celled or multi-cellular, microscopic organism with cell nuclei, and which aren't plants, animals, or fungi. Multi-cellular protists live as colonies, without specialization. They have many ways of moving around, including flagella, cilia, and amoeboid action. They have multiple ways of reproducing, and some have quite complex life cycles. But they have membrane-wrapped organelles and an outer cell membrane.
Several parasitic protists can cause deadly diseases, including malaria, amoebic dysentery, and giardia. But the human body is also home to beneficial and neutral protists. Viruses are microscopic particles made of nucleic acids, proteins, and sometimes lipids. We begin to be colonized by bacteria during birth. During the birth process and immediately after birth, we get our first microorganisms.
All babies also acquire bacteria from the skin of the nurses and medical doctors and the environment they live in. After babies begin to eat, they get microbes from their diet.
In the first days of life, the type of the microorganisms that colonize their intestines will be different, depending whether the baby is breast feeding or drinking formula. As babies grow, they get microorganisms from the solid food they eat, from crawling on the floor, from putting their hands in their mouths, from licking toys, and from many other sources!
The microbes that live in the human body change during our growth, until we are 3 years old. At that point, the microbiota becomes more or less stable until adult life. Each individual has his or her own microbiota, which depends in part, but not only, on the types of food eaten, the environment where the person lives, and the other people and animals that the person interacts with Figure 3 [ 2 , 3 ].
When we mention bacteria in the human body, you might immediately think of a disease, called a bacterial infection. At some point in your life, you have probably had an infection that was treated by antibiotics prescribed by your doctor. Antibiotics are medicines that kill or prevent the growth of bacteria.
However, the majority of the microbes are harmless and actually help to maintain our health. The microbes of the skin, mouth, and nose fight against bad bacteria that want to enter the body to cause disease. These good bacteria act like guards that keep away the harmful bacteria that make us sick.
The bacteria that colonize the vagina are another example of good bacteria. They maintain an acidic environment in the vagina that prevents the growth of other microorganisms that might cause disease.
Disease-causing microorganisms are called pathogens. Even though most of the time they are harmless or even helpful, in certain conditions some of the bacteria that are part of the human microbiota can harm us. For example, bacteria that live on the skin can become a problem.
If you cut yourself, the bacteria that live on the surface of your skin may be able to enter into your body through the cut, getting in where they do not belong. In this instance, these bacteria sometimes might be harmful to the body and trigger an infection. Symptoms of an infection include pain, swelling, redness, and fever.
Another example of how the microbiota can harm us is when you let too many bacteria accumulate in your mouth. These bacteria can stick to the surface of your teeth. Some types of bacteria will produce acidic products from the food you eat especially sugars that can destroy your teeth and gums.
That is why we need to brush our teeth at least two times a day for 3 min to avoid the multiplication of bacteria that can cause painful disease and, in severe cases, loss of teeth. As we mentioned earlier, the intestines contain the largest portion of the human microbiota.
The intestinal microbiota produces some vitamins that are good for us, such as vitamins B12 and K. These vitamins are not produced by human cells. The intestinal microbiota also helps in the digestion of food and protects the intestinal walls from invasion by pathogens. There is a lot of research going on about the role of the intestinal microbiota. We are still trying to understand how the human microbiota contributes to health and disease.
In general, healthy humans have a balanced microbiota, with a high diversity of bacteria in their guts. This means that they have a mix of different types of bacteria with different shapes, sizes, function, and names. More than 1, different types of bacteria exist in the human gut! By contrast, when only a small diversity of bacteria is present, meaning that only a few types of bacteria exist in the gut, in higher numbers than normal, disease may occur.
Different levels of diversity in the gut bacteria may be related to obesity the state of being extremely overweight , which can begin in childhood. Abnormal diversity in the intestinal microbiota may also play a role in the development of diabetes increased sugar in the blood , asthma long-lasting difficulty with breathing , and painful diseases in the intestine chronic gut inflammation , among others [ 4 ].
Meanwhile, the Actinobacteria phylum includes the Bifidobacterium bifidum species, which is generally beneficial for healthy individuals.
This list, however, is by no means exhaustive. There are around 2, bacterial species in the human gastrointestinal tract, according to compiled data. If some of these names sounded uncomfortably familiar, it is because many of these bacteria can cause infection if they over-colonize. And some strains can infect the gut through food that has gone bad or contact with unclean surfaces.
Some strains of E. But gut bacteria can typically be strong allies in health maintenance, and specialists continue to study the many ways in which these microorganisms help keep us in good form. Elizabeth Hohmann in an interview with Harvard Medical School. Other microorganisms present in the gut are viruses, but not the ones that typically cause illness.
Still, much about them remains poorly understood. The oral microbiota contains 12 bacterial phyla — Firmicutes , Fusobacteria , Proteobacteria , Actinobacteria , Bacteroidetes , Chlamydiae , Chloroflexi , Spirochaetes , SR1 , Synergistetes , Saccharibacteria , and Gracilibacteria — with multiple species, named or unnamed. But the mouth also houses other microorganisms, namely protozoa, the most common of which are Entamoeba gingivalis and Trichomonas tenax , as well as fungi and viruses.
There are 85 genera of fungi in the oral environment, including Candida, Cladosporium, Aureobasidium, Saccharomycetales, Aspergillus, Fusarium , and Cryptococcus. As with other microbiota, if the numbers of microorganisms that populate the mouth become imbalanced, it can lead to the development of illness, such as various bacterial infections. Recent studies indicate that the components of bacterial populations in the vagina may not only fluctuate at different stages of the menstrual cycle, but may also vary among individuals of different races and ethnicities.
Some types of bacteria identified in the vaginal canal include Lactobacilli , Prevotella , Dialister , Gardnerella , Megasphaera , Eggerthella , and Aerococcus. This is why specialists advise extreme care when it comes to intimate hygiene: Many products can destroy the delicate bacterial balance in the area. Furthermore, little is known about the microbiota of the uterus. Scientists have only started to study it recently and, so far, only in small cohorts. One study found that Lactobacillus and Flavobacterium appeared to be the most common bacteria in the uterus, regardless of whether a woman is pregnant.
More in-depth research is ongoing. Little is also known about the microbiota of the female bladder and urethra. Following recent investigations, it appears that the most common types of bacteria in the female urethra are Lactobacillus , followed by Gardnerella, Corynebacterium, Streptococcus , and Staphylococcus.
And while some researchers suggest that the microbiota of the bladder and female urinary tract are largely the same, others beg to differ. One study published this year in the Journal of Urology has found significant differences.
Its authors also hypothesize that the bacterial populations of the female lower urinary tract may vary with age, level of sexual activity, and whether or not the person has entered menopause.
If researchers still know little about the microbiota of the female urogenital areas, they appear to know even less about those present in the male urogenital regions.
A PLOS One study from found differences in microbial communities on circumcised, compared with uncircumcised, penises, in a culture-independent investigation. More specifically, bacteria of the Clostridiales and Prevotellaceae families appeared to be more abundant on uncircumcised penises.
Cindy Liu in an interview. Other than this, very little is understood about the penile microbiota. In the same interview, Prof. Deborah Anderson, who teaches obstetrics, gynecology, and microbiology at the Boston University School of Medicine, commented that:. A review — published in Nature Reviews Microbiology in — explains that the bacterial populations vary widely by skin region and also depend on a range of factors, such as the moisture of the skin and the amount of natural oil, or sebum.
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