Neisseria gonorrhoeae gram stain

Neisseria gonorrhoeae, commonly known as gonococcus, is a gram-negative diplococcus bacterium that is primarily responsible for the sexually transmitted infection, gonorrhea. 

Gram staining is a technique used to investigate the nature of the cells in a sample and to differentiate between different bacterial species. 

It is a vital tool for diagnosing Neisseria gonorrhoeae, as well as for studying its structure and function. 

We will explore how gram staining is used for detecting Neisseria gonorrhoeae and its importance.

Tools for gram staining

  • Glass slides 
  • Gram stain reagents 
  • Wire loop 
  • Water
  • Burner

Neisseria gonorrhoeae gram staining procedure

Preparation of the bacterial smear:

A bacterial smear must first be prepared before performing a gram stain. This entails placing a small amount of the Neisseria gonorrhoeae specimen on a microscope slide. 

The specimen is then spread out to form a thin, even layer of bacterial cells, known as a bacterial smear. The smear is then heat-fixed, which involves passing the slide three times through the flame of a Bunsen burner. 

Heat fixing kills the bacteria, causes them to adhere to the slide, and coagulates the bacterial proteins, preventing them from being washed away during the staining process.

Primary Stain:

It is the stain applied to the Neisseria gonorrhoeae smear staining procedure. In this case, the primary stain is crystal violet. It is a basic dye that binds to the negatively charged bacterial cell wall.

Crystal violet is added to the Neisseria gonorrhoeae smear and allowed to sit for one minute. During that time, the stain will penetrate all bacterial cell walls, turning them purple when viewed under a light microscope.


Next, an iodine solution is applied to the smear as a mordant, which means that it helps to intensify the staining by binding the crystal violet more tightly to the bacterial cells. 

Neisseria gonorrhoeae gram stain reaction: Inside the bacterial cell wall, the iodine solution forms a stable complex with crystal violet. 

This helps to keep the dye from washing away during the subsequent decolorization step. The decolorization step entails washing the smear with alcohol or acetone, which removes crystal violet from some but not all bacterial cells.


Typically, ethanol or acetone is used as a decolorizer in the Gram staining procedure. 

The decolorizer is added after the mordant and is responsible for removing the crystal violet-iodine complex from the outer membrane of Neisseria gonorrhoeae, whereas the complex remains trapped within Gram-positive bacteria’s thicker peptidoglycan layer.

The bacterial cell wall’s differential affinity for the crystal violet-iodine complex and the decolorizer is what allows the final staining color to distinguish between the two groups – Gram-positive bacteria appear purple, while Gram-negative bacteria appear pink.


Finally, the smear is stained with a counterstain such as safranin. The safranin colorizes the decolorized Neisseria gonorrhoeae cells pink-red, whereas the crystal violet-iodine complex remains in the intact cell walls of other bacterial cells, which appear purple-blue. 

This differential staining process distinguishes Gram-positive bacteria, which retain the crystal violet-iodine complex and appear purple-blue after counterstaining, from Gram-negative bacteria, which do not retain the complex and appear pink-red.


Neisseria gonorrhoeae gram stain morphology/shape

The morphology of Neisseria talks about its shape or structure after gram staining was done on it. When viewed under a microscope, Neisseria gonorrhoeae appear as pairs of cocci (spherical cells). The cells are typically kidney-shaped and can be observed within white blood cells during an infection.

Importance of Neisseria gonorrhea gram staining

The following are the importance of Neisseria gonorrhea gram stain.

  • Accurate identification: Gram staining for Neisseria gonorrhoeae is an important step in the laboratory diagnosis of gonorrhea. It helps to differentiate it from other types of bacteria that may cause similar symptoms but stain differently when stained with the Gram staining method.
  • Treatment options: Neisseria gonorrhoeae is resistant to some antibiotics, and Gram-negative bacteria are generally considered more difficult to treat than Gram-positive bacteria. As a result, the Gram staining test results can aid in the selection of appropriate antibiotics for treatment.
  • Management of gonorrhea: Early treatment of gonorrhea is critical for preventing infection spread, and proper laboratory methods such as Gram staining can aid in accurate diagnosis and management.

Neisseria gonorrhoeae virulence factors

Neisseria gonorrhoeae has some virulence factors that allow it to infect humans. The following are some of the most important virulence factors of Neisseria gonorrhoeae: 

  • Fimbriae and Pili: Neisseria gonorrhoeae produces fimbriae and pili, which are long, thin, hair-like structures that allow the bacteria to attach to and invade human cells. These structures also aid bacteria in evading the immune system and resisting antimicrobial clearance. 
  • Lipooligosaccharide: LOS is a complex carbohydrate and lipid molecule found on the surface of Neisseria gonorrhoeae. It is a significant virulence factor that aids bacteria in resisting complement-mediated killing by the host immune system.
  • IgA protease: Neisseria gonorrhoeae produces an enzyme known as IgA protease, which can cleave and inactivate IgA antibodies. The bacteria are thus able to avoid detection and destruction by the host immune system. 
  • Antigenic variation: Antigenic variation is a process by which Neisseria gonorrhoeae can change the surface expression of its fimbriae and LOS molecules. This allows the bacteria to avoid detection and elimination by the host immune system. 
  • Type IV secretion system: Neisseria gonorrhoeae has a type IV secretion system, which enables it to inject bacterial proteins and DNA directly into human cells. This allows the bacteria to manipulate host cell signaling pathways to promote survival and replication within host tissues.

What cell structures does Neisseria have?

Neisseria is a gram-negative bacterium with a variety of cell structures, including

  • Outer membrane: The outer membrane of Neisseria surrounds the cell wall and separates the bacterium from its surroundings. Lipopolysaccharides (LPS), porin proteins, and other molecules found in the outer membrane play important roles in virulence and immune evasion. 
  • Cell wall: Neisseria, like all bacteria, has a cell wall that provides structural support as well as protection from osmotic stress. The cell wall of Neisseria, on the other hand, has distinct characteristics, including peptidoglycan that is highly cross-linked and contains unusual amino acids such as diaminopimelic acid. 
  • Capsule: Some Neisseria strains can produce a polysaccharide capsule that protects the bacterium from host immune defenses.
  • Pili and fimbriae: Pili and fimbriae are long, thin, hair-like structures that protrude from the cell surface produced by Neisseria. These structures allow the bacterium to cling to host tissues while evading immune defenses. 
  • Flagella: Some Neisseria strains are motile, with flagella that allow them to move through liquid environments. 
  • Cytoplasmic membrane: The cytoplasmic membrane of Neisseria is a phospholipid bilayer that separates the cytoplasm from the surrounding environment. It contains numerous transporters and receptors involved in nutrient uptake, signal transduction, and other cellular processes.

What gonorrhea uses to attach and enter host epithelial cells?

Neisseria gonorrhea uses cell surface-associated structures such as pili and cell wall adhesins to attach to and enter host epithelial cells. The bacteria must be free from sialic acid to successfully bind and enter the cells.

Where is Neisseria gonorrhoeae found in nature?

Neisseria gonorrhoeae is a bacterium found only in humans that is transmitted through sexual contact. Outside of the human body, it is not found in nature.

What Next?

The Gram stain is a useful diagnostic tool for identifying and characterizing N. gonorrhea, which is necessary for proper treatment and infection control. 

The causative agent of the sexually transmitted infection gonorrhea, Neisseria gonorrhoeae, is a gram-negative diplococcus that appears under a microscope as two round cells joined together after a Gram stain procedure. 

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Last Updated on July 8, 2023 by Our Editorial Team