Lecture notes in Microbiology

Bacterial Cell Surface Structures and Appendages (Flagella, Fimbriae and Pili)


Fimbria vs pilus

Cell Surface Appendages of Bacteria
(Flagella vs Fimbriae vs Pili of Bacteria)

What are cell surface appendages?

Cell surface appendages (aka filamentous appendages) are proteinaceous tubular or fibrous structures found on the surface of bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as locomotion, attachment, adhesion and assisting in genetic exchange.

What are the three types of cell surface appendages of bacteria?

The THREE types of cell surface appendages are present on bacteria. The classification is based on the relative length of the appendages, composition and function. The three cell surface appendages of bacteria are

(1).  Flagella

(2).  Fimbriae

(3).  Pili

(1). Flagella

Bacterial Flagella definition: Bacterial flagella are long whip-like filamentous structures present in some bacteria. The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion.

What are the characteristics of bacterial flagella?

Ø  Flagella are long whip-like filamentous structures.

Ø  Flagella are many times longer and thicker than Fimbriae and Pili.

Ø  Approximate length of flagella varies from 15 to 20 µm.

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Lecture notes in Microbiology

Difference between Pili and Flagella of Bacteria- A Comparison Table


Fimbria vs pilus

Flagella vs Pili of Bacteria: A Comparison Table
(Similarities and Differences between Pili and Flagella of Bacteria)

Both Flagellum (plural Flagella) and Pilus (plural Pili) are the filamentous proteinaceous structures found on the surface of some bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as motility, attachment, adhesion and assisting in genetic exchange.

Flagella definition: Bacterial flagella are long whip-like filamentous structures present in some bacteria. The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals in the external environment of the cell. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion.

Pili definition: Pili are long hair like tubular micro-fibres like structures present on the surface of some Gram-negative bacteria. They are comparatively shorter filamentous structures than flagella and their number per cell is very limited. There are many classes of pili based on their structure and function. Most of the pili can act as the receptors of some viruses.

The present post describes the Similarities and Differences between Flagella and Pili with a Comparison Table

Similarities between Flagella and Pili

Ø  Both flagella and pili are filamentous structures.

Ø  Both are cell surface appendages.

Ø  Both are made up of proteins.

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Lecture notes in Microbiology

Difference between Flagella and Fimbriae of Bacteria- A Comparison Table


Difference between Fimbriae and Flagella

Fimbriae vs Flagella
(Similarities and Differences between Fimbriae and Flagella of Bacteria)

Both Fimbria (plural Fimbriae) and Flagellum (plural flagella) are the filamentous proteinaceous structures found on the surface of some bacterial cells. 

Fimbriae definition: Fimbriae are bristle like short fibres occurs on the surface of some Gram positive and Gram negative bacteria. Fimbriae enable the bacterial cell to stick to the surface of host cells. They also help in the formation of pellicles or biofilms. (Pellicle: thin sheet of cells on the surface of a liquid).

Flagella definition: Bacterial flagella are long whip like filamentous structures present in some bacteria. The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals in the external environment of the cell. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure and formation and mechanism of propulsion.

The present post describes the Similarities and Differences between Fimbriae and Flagella of bacteria with a Comparison Table.

Similarities between Fimbriae and Flagella

Ø  Both fimbriae and flagella are filamentous structures.

Ø  Both are present in Gram positive and Gram negative bacteria.

Ø  Both are cell surface appendages, present on the cell surface of bacteria.

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Lecture notes in Microbiology

Difference between Pili and Fimbriae of Bacteria- A Comparison Table


Difference between Pili and Fimbriae

Fimbriae vs Pili
(Similarities and Differences between Fimbriae and Pili of Bacteria)

Both Fimbria (plural Fimbriae) and Pilus (plural Pili) are the filamentous proteinaceous structures found on the surface of some bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as attachment, adhesion and assisting in genetic exchange.

Fimbriae definition: Fimbriae are bristle like short fibres occurs on the surface of some Gram positive and Gram negative bacteria. Fimbriae enable the bacterial cell to stick to the surface of host cells. They also help in the formation of pellicles or biofilms. (Pellicle: thin sheet of cells on the surface of a liquid).

Pili definition:  Pili are long hair like tubular micro-fibres like structures present on the surface of some Gram negative bacteria. They are comparatively longer filamentous structures and their number per cell is very limited. There are many classes of pili based on their structure and function. Most of the pili can act as the receptors of some viruses.

The term Pili and Fimbriae are used inter-changeably by many authors in many microbiology text books. However, modern studies have clearly shown that they are two different entities in the bacteria distinguished by their development, structure and functions.

The present post describes the Similarities and Differences between Fimbriae and Pili with a Comparison Table

Similarities between Fimbriae and Pili

Ø  Both fimbriae and pili are filamentous structures.

Ø  Both are cell surface appendages, present on the cell surface of bacteria.

Ø  Both are the attachment or adhesion organs in bacteria.

Ø  Both are made up of proteins.

Continue reading