The Normal Flora of Human body and its 5 beneficial effects.

Written by SouravBio · 7 minutes read >

We are all familiar with this term Normal Microbial Flora or Human microbiome, but we don’t know the real benefits of normal microflora, so in this article, I will discuss the benefits of normal microbial flora in the human body, and how they benefit us.

First of all, we have to know What is Normal Flora? so I will discuss every detail about microflora step by step if you face any problem then feel free and comment in the below section.

All the microorganisms are not harmful for example, our body surface contains different varieties of microorganisms in a large number, which are provides benefits to our body.

The normal microbiota of a human body is not static. They are started to colonize in our body after birth, and they constantly change with the human ages.

When a new-born comes in contact with the environment, microorganisms instantly started to colonize in the body surface. After that, the number of microorganisms is started to increase constantly with the human age as you can see in this below table.

Definition of Normal Flora

Normal Microbial flora defines as those microorganisms which are present in the human body in a huge number.

Our environment contains a huge number of microorganisms, whenever we exposed to the environment our body surface gets in contact with those microorganisms, and they are started to colonize in our body surface. Except for surface microflora, microorganisms also present in our vital organs, including the liver, gastrointestinal tract, mouth, urinary tract, etc. In the case of a healthy person, all the initial tissues (blood, brain, muscle, etc) are normally free of microorganisms.

In one sentence, all the microorganisms are present in our anatomical sites, are defined as Normal Flora.

The normal flora of microorganisms is consisting of eukaryotic fungi, protists, bacteria, etc. Among them, bacteria are present in large numbers.

Types of Normal Microflora

There is a present different type of Normal flora in the human body, including bacteria, fungi, archaea, viruses.


The initial studies show that an individual contains thousands of bacteria on their body surface and vital organs. The mouth and the gut portion of the human body contains a large number of bacteria, which is greater than the bacterial population of Skin and vaginal sites. There are present different species of bacteria that are found in the human body, which are vary based on the type of organs.


Archaea mainly found in the gut portion of the human body. The species of archaea is much more limited in our body.


They are mainly found at the gut portion and skin of the human body.


Viruses, including bacterial viruses (bacteriophages), are colonize in our various body parts, such as skin, gut, lung, oral cavity, etc.

Normal Flora of Human Body

Microorganisms are present in different parts of our body such as skin, eye, nose, mouth, gastrointestinal tract, etc. We discussed the normal flora of each body part in below.

Normal Flora of Human Body
Normal Flora of Human Body

Normal Flora of Skin

An adult human body has approximately 2 m2 of skin, and it contains about 10^12 numbers of bacteria.


There are present different types of bacteria on our skin surface. The diversity of bacteria is vary based on the different locations of our skin. Our skin is divided into three parts: The dry portion, the moist portion, and sebaceous (containing sebum).

The dry portions of our skin include forearm, buttocks, hands, etc. This portion contains the greatest diversity of gram-negative and gram-positive bacteria, such as Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria.

The moist areas of our skin include umbilicus, underarm, inguinal and gluteal creases, and inside the elbow, etc. These portions of the skin exhibit less diversity of microorganisms. It contains mostly some Firmicutes and Actinobacteria such as Staphylococcus and Corynebacterium spp.

The oily sebaceous sites contain the lowest diversity of bacteria including most members of Actinobacteria (Propionibacterium spp.). The oily portions of our skin include the forehead, behind the ear, and the back.

Some occasionally pathogenic bacteria are present in our skin surface such as;

  • Staphylococcus epidermidis
  • Staphylococcus aureus
  • Staphylococcus warneri
  • Streptococcus pyogenes
  • Streptococcus mitis
  • Cutibacterium acnes
  • Corynebacterium spp.
  • Acinetobacter johnsonii
  • Pseudomonas aeruginosa


Except bacteria, our skin also contains more than 14 different genera of fungi, including;
dermatophytes (skin living fungi) such as Microsporum gypseum, and Trichophyton rubrum and nondermatophyte fungi (opportunistic fungi that can live in the skin) such as Rhizopus stolonifer, Trichosporon cutaneum, Fusarium, Scopulariopsis brevicaulis, Curvularia, Alternaria alternata, Paecilomyces, Aspergillus flavus and Penicillium species.

Normal Microflora of Nose, and Pharynx.

The nasopharynx is a part of the pharynx lying above the level of the soft palate. The normal flora of Pharynx is including some potential pathogenic bacteria such as Streptococcus pneumonia, Neisseria meningitides, and Haemophilus influenza. Also, a large number of non-pathogenic Gram-positive bacteria are commonly found in both the nose and nasopharynx.

Normal flora of Mouth

The mouth has an optimum environment (water, nutrients, neutral pH, and moderate temperature) which will help in the growth of Microorganisms. The mouth portion of the human body contains mostly the genera of some Streptococcus, Neisseria, Actinomyces, Veillonella, and Lactobacillus, as well as some yeasts.

Normal flora of Throat

The microbial flora of throat is including non-hemolytic and alpha-hemolytic streptococci, some Neisseria species, staphylococci, diphtheria and Hemophilus organisms, pneumococci, yeasts, and Gram-negative rods.

Normal flora of Respiratory Tract

Our lower and upper portion of the respiratory tract is free of microorganisms because there are three important reasons such as;

  1. A continuous stream of mucus entraps the microorganisms, and the ciliated epithelial cells continually move the entrapped microorganisms out of the respiratory tract.
  2. Alveolar macrophages destroy the microorganisms.
  3. A bactericidal effect is exerted by the enzyme lysozyme, present in the nasal mucus.
    The enzyme lysozyme (nasal mucus) shows a bactericidal effect that kills all the bacteria.

Normal flora of Eye

A small number of bacteria are present in eye including;

  • Chlamydia trachomatis
  • Chlamydophila pneumonia
  • Haemophilus aegyptius
  • Haemophilus influenza
  • Moraxella app
  • Neisseria app
  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Streptococcus viridians.

Normal Flora of Gastrointestinal Tract

Due to the presence of very low acidic pH (2 or 3), the stomach contains few bacteria including Streptococcus, Staphylococcus, Lactobacillus, Peptostreptococcus app.

The small intestine also contains several bacteria such as; Enterococcus faecalis, lactobacilli, diphtheroid, and the yeast Candida albicans are occasionally found.

The large intestine contains a huge population of microorganisms. More than 400 species of bacteria were isolated from human feces. Most of them are anaerobic, Gram-negative bacteria, and Gram-positive rods. Al those bacteria belong to the genera of Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.

There also present several fungi such as Candida, Saccharomyces, Aspergillus, Penicillium, Rhodotorula, Trametes, Pleospora, Sclerotinia, Bullera, and Galactomyces.

Normal Flora of Urinary tract

Both the male and female urinary tract contains a huge number of microorganisms such as;

1.Microbial flora of Male Urinary tract or Distal Urethra

Male Urinary tract contains these following microflora;

  • Coagulase-negative staphylococci
  • Diphtheroid
  • Streptococcus spp.
  • Mycobacterium spp.
  • Bacteroides spp.
  • Fusobacterium spp.
  • Peptostreptococcus spp.

2. Microbial flora of Female Urinary tract Vigna

Female Urinary tract contains these following microflora;

  • Lactobacillus spp.
  • Peptostreptococcus spp.
  • Diphtheroid
  • Candida spp.
  • Gardnerella spp.
  • Bacteroides spp.
  • Streptococcus spp.
  • Clostridium spp.

Beneficial Effects of the Normal Flora

The Normal flora of the human body provides serval benefits, which are discussed below;

1.Prevent Pathogens

Most importantly Normal flora prevents the colonization of Pathogens by competing with them for essential nutrients and attachment sites.

2. Vitamin Synthesis

Some normal microflora synthesis vitamins for their own need. Sometimes our body absorbs those vitamins as a nutrient.

Example: Some enteric bacteria of the human body produce Vitamin K and Vitamin B12. Lactic acid bacteria also produce certain B-vitamins.

3. Killing bacteria

Some normal flora antagonizes other bacteria by producing some substances which inhibit or kill nonindigenous species.

Example: few intestinal bacteria produce some substances which have highly specific bacteriocins, that helps to kill other bacteria.

4. Development of certain tissues

Normal flora also helps in the development of certain tissues.

Example: Caecum and certain lymphatic tissues (Peyer’s patches) in the gastrointestinal tract.

5. Production of Antibody

The normal flora of the human body also helps to stimulate the synthesis of normal antibodies.

Example: When The normal flora acts like an antigen in our body, they induce an immunological response, in particular, an antibody-mediated immune (AMI) response, which induces the production of natural antibody.

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