Microflora of Human Body

Internal tissues including blood, brain, muscle, etc. in a healthy person are often clear of germs. Skin and mucous membranes, which are surface tissues, are continuously in contact with environmental organisms and are therefore easily colonised by different microbial species. The term normal flora refers to the collection of organisms typically present in any anatomical region. There are a few eukaryotic fungi and protists in the normal flora of humans, but bacteria are the most prevalent and observable microbial species in the normal microflora.

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Normal Microflora

The population of microorganisms that live on healthy normal people’s skin and mucous membranes is referred to as their normal microbial flora. There are two categories of microorganisms that are constantly present in the skin and mucous membranes:

  • If disturbed, the resident flora quickly reestablishes itself because it is made up of relatively stable species of microorganisms that are typically found in a certain location at a given age.
  • The transitory flora, which is generated from the environment, is made up of nonpathogenic or possibly pathogenic bacteria that live on the skin or mucous membranes for a short period of time, but do not cause disease or become established permanently on the surface.

Microflora of Skin

The skin is home to a wide variety of microorganisms, most of which are benign or even helpful to the host. It is most likely to carry transitory flora due to its frequent exposure to the environment. However, there is a consistent and distinct resident flora that is altered in various anatomical regions by secretions or exposure to mucosal membranes. Such microflora of human skin are:

  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Corynebacterium spp
  • Propionibacterium spp
  • Micrococcus spp

Microflora of Upper Respiratory Tract and Buccal Cavity

In the mouth, yeast (Candida species) is present. Even in teeth, several anaerobes such as Provotella spp, Fusobacterium spp, Lactobacilli and several anaerobic vibrios are seen.

Significant Staphylococci such as S.epidermidis and S.aureus, Corynebacteria and Streptococci make up the nose’s flora. Likewise, an adult human’s tonsillar tissue and gingivae typically contain Actinomyces species and other protozoa. Other predominant microbes in the upper respiratory tract are Neisseriae, mycoplasmas, pneumococci and diphtheroids.

The ciliated epithelium that lines the lower respiratory tract, which includes the bronchi, trachea and pulmonary tissues, performs an effective cleansing function that keeps the area almost free of microbes.

Microflora of Intestine

The relative makeup of the intestinal and faecal flora is significantly influenced by diet.

For instance, it has been demonstrated that those who consume an animal-based diet have higher concentrations of bile-tolerant microbes such as Bilophilia and Bacteroides and lower concentrations of Firmicutes which break down dietary plant polysaccharides.

Only Helicobacter pylori survive in the acidic environment of the human stomach out of the hundreds of phylotypes found there.

The phylum Bacteroidetes and members of the order Clostridiales are among the bacteria found in the upper intestine’s mucosa, whereas Enterococci and Enterobacteriales can be found in the lumen.

Do Check: Difference between Virus and Bacteria

Microflora of Vagina

Aerobic lactobacilli enter the vagina shortly after birth and survive as long as the pH is acidic.

A mixed flora of cocci and bacilli is present when the pH reaches neutral and it stays that way until adolescence. Then there is an increase in anaerobic and aerobic lactobacilli during puberty.

Following menopause, the population of lactobacilli again declines, and a mixed flora reemerges.

Other Human Microflora

  • Diphtheroids, S.epidermidis and Enterococcus are regularly detected in the human anterior urethra. Likewise, E. coli, Proteus and Neisseria are also infrequently discovered there.
  • Diphtheroids and S.epidermidis are also predominant in the conjunctiva. Conjunctival pathogens that do cause infection include Chlamydia trachomatis and Neisseria gonorrhoeae. Usually, the regular tear flow, which contains the antimicrobial lysozyme keeps the conjunctival flora under control.
  • The flora in the colon (large intestine) is qualitatively comparable to that in faeces. However, the predominant species are Coliforms (E.Coli) and other microbes include anaerobic Bacteroides, Enterococcus, Clostridia and anaerobic lactic acid bacteria in the genus Bifidobacterium.

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Frequently Asked Questions


Describe normal flora of the human body.

The human body is colonised by several bacterial species. The bacteria or microbes that thrive in the healthy human body without causing disease are termed as normal flora or microflora.

What are firmicutes?

Firmicutes or Bacillota are a class of bacteria with gram-positive cell walls. This group comprises some well-known pathogens and they can be found in diverse environments. This group includes several Bacilli and Clostridia.

Name some microbes that digest plant polysaccharides.

Some microbes that break plant cell walls are Eubacterium rectale, Ruminococcus bromii and Roseburia.

Is the placenta devoid of microbes?

The healthy placenta was once thought of as a sterile organ. But many nonpathogenic commensal bacteria thrive in the placenta. Also the placental microbiome is more similar to the oral microbiome than the rectal and vaginal microbiomes. Many scientists believe that the presence of microbes in placenta is due to contamination.