Are Bacteria Extracellular? 9 Facts You should Know


This article illustrates the complete information about extracellular bacteria. Bacteria is single-celled, free living a no and ubiquitous (found almost every part on earth).

Extracellular bacteria exist in their environmental niche as a free-living micro-organism.

What are extracellular bacteria?

The extracellular bacteria are the pathogens which present outside the cell, they do not invade into the cell. The bacteria grow in the extracellular environments which is rich in body fluids.

Some extracellular bacteria like Vibrio cholerae do not penetrate in to the cell but attached to the outer membrane epithelial surfaces, infect the cell by secreting potent toxin and caused diseases. The extracellular bacteria do not survive into the cell but they took its nutrition from the host cell

How are bacteria extracellular?

A good knowledge of the interaction between host cell and bacteria pathogen is required to identify the different type of bacteria involved. The extracellular bacteria enter into the host body by any entry portal mainly a fluid medium at injury site.

These bacteria will multiply at the extracellular site of host such as vascular lymphatic, mucosal surfaces, body cavity fluids and interstitial spaces. Virulence mechanisms is used by extracellular bacteria to evade the phagocytosis and humoral immunity that help to promote the extracellular multiplication.

Are all bacteria extracellular?

The pathogen bacteria are classified into two main categories: the extracellular bacteria and intracellular bacteria. The intracellular bacteria will replicate into the host cell follow cytosolic and vacuolar pathway for replication. The extracellular bacteria multiply outside the cell medium.

From the total population of bacteria some are extracellular and rest are intracellular in nature. Depend on the host and pathogen bacteria interaction identified as extracellular or intracellular.

Which type of bacteria is extracellular?

The extracellular bacteria are the bacteria that proliferate in the external environment of the host cell. they get their food or nutrition from the extracellular fluid present outside the cell or at intercellular spaces (present between two cells).

The bacterial cell interacts with host cell define its nature as if it interacts with cell outside the cell is extracellular bacteria or if invade in the cell and cause pathogenicity is intracellular. The extracellular bacteria secrete its toxin outside the cell and cause pathogenicity or infect the host.

Examples of extracellular bacteria

Many kind of extracellular bacteria are present in the ecosystem including in human body. Human body itself is full of gut bacteria. The extracellular bacteria promote by extracellular multiplication by avoiding phagocytosis

Some of the extracellular examples are Staphylococcus aureus, Psedomonas aeruginosa, Salmonella spp., Vibrio cholera, Shigella spp., enterohemorrhagic Escherchia coli, Pseudomonas spp., Klebsiella pneumoniae, Neisseria meningitidis, Helicobacter pylori etc.

extracellular bacteria examples from shutterstock

Growth of extracellular bacteria

Once the extracellular bacteria enter into the cell, first of all neutrophil cell are released by the host immune system to do phagocytosis. But the extracellular bacteria resist the phagocytosis ( early engulfment of pathogen) that favour the survival of pathogen bacteria.

The extracellular bacteria resist phagocytosis by generation of toxins, forming hydrophilic capsule, presence of M-protein and hylouronic acid. The potent toxin produced by the some extracellular bacteria lethal to leucocytes and their host cells. Some extracellular bacteria survive by forming slippery hydrophilic antiphagocytic capsule e.g. pneumococci resist attachment to neutrophle by forming hydrophilic capsules. the bacteria S. pyogene, phagocytosis resist by the presence of M- Protein and hylouronic acid.

Extracellular bacteria digestion

The extracellular bacteria perform digestion by secreting the enzyme outside the cell the then absorb the digested food. The digestion is the process of breakdown of complex food into simpler food in absorbable form by the enzymatic action.

The hydrolytic enzymes are secreted on the extracellular matter of cell and then the digested and simpler matter is absorbed by the cell wall of the bacteria . as the digestion is not take place inside the cell so it is called extracellular digestion. Hence, in this way the extracellular bacteria referred as decomposers.

Structure of extracellular bacteria

The extracellular bacteria live outside the cell. they have to respond according to its environment for their survival and reproduction. For example, response of the bacteria toward food, away from toxins and when environmental condition is not favorable shut down its machinery. The extracellular bacteria have special cellular features that help to cope up with their environment.

Many extracellular bacteria have an extra polysaccharide coating that is present outside the cell wall.it is not easily wash off and well organized called capsule. Another layer which is easily wash off and more disorganized also present called slime layer. The function of capsule and slime layer to protect the bacteria from he outside environment like from antibiotics, host immune response and drying out.

An S- layer is present is made of protein or glycoproteins present in a tiled or floor like manner.it is important to maintain the cell shape. The extracellular bacteria have many fimbria ,a short hair-like structure that help of attachment to the host cell and colonization. it is also call pili. Flagella is long, thin protein structure that comes out from the plasma membrane. It help in movement of bacteria. Some extracellular bacteria will form endospore for their survival from the outside environment . The cell wall of bacteria is made of peptidoglycan which is present immediate outside of plasma membrane. The cell wall of bacteria is responsible for rigidity of bacteria.

The bacterial cytoplasmic membrane is made up of phospholipids act as permeability barrier to most the substances.

Are bacteria Extracellular
Bacterial cell from Shutterstock

Intracellular v/s extracellular bacteria

the intracellular bacteria are the bacteria which invade the host cell and grow, replicate inside the cell and cause pathogenicity.

  • The extracellular bacteria are free-living but the intracellular bacteria replicate either inside the host cell or in an environment niche.
  • The extracellular bacteria will attach to the host cell surface and intracellular bacteria will invade into the cell and release potent toxin
  • The extracellular bacteria do not penetrate the cell membrane while intracellular bacteria penetrate the cell membrane
  • The extracellular bacteria live outside the environment but intracellular bacteria require the living cell to survive.
  • Examples of extracellular bacteria are Escherchia coli, N. meningitidis, Shiegilla sp, S. aureus , intracellular bacteria examples are Chlamydia spp., Anaplasma spp., Ehrlichia spp., rickettsia spp., Orientia spp.
  • The population of extracellular bacteria is less as compare to the intracellular bacteria.
  • The extracellular bacteria adhere to host cell surface by the means of fimbria which is usually absent in the intra cellular bacteria.

Tanu Rapria

Hi..I am Tanu Rapria, I have completed my Master's in Biotechnology. I always like to explore new areas in the field of Biotechnology. Apart from this, I like to read, travel and photography.

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