What Is Gram Negative Bacteria & Why Can It Cause So Many Diseases

Whats the difference between Gram-Negative and Gram-Positive Bacteria?

In microbiology Gram staining is used to characterize bacteria into two different groups based on their cell walls. These groups are gram-positive and gram-negative bacteria. Under a microscope gram-positive bacteria appear to have a purple cell wall. This is due to a thick layer of peptidoglycan in their cell walls, which retains the gram stain used during the procedure. Gram-negative bacteria, however, appear to have a pink cell wall, due to their thin layer of peptidoglycan, which allows the stain to wash out.

Gram Negative bacteria under the microscope

Figure 1: Gram-negative bacteria under the microscope

Why Does Gram-Negative Bacteria Cause Disease?

Gram-negative bacteria are more pathogenic than gram-positive bacteria because of their outer membrane. The outer membrane of gram-negative bacteria is strong and protects the cell against outside attacks, while gram-positive bacteria does not have this feature. Gram-negative cells also contain an enzyme that destroys penicillin, making treatment with antibiotics such as amoxicillin difficult.


How Does Gram-Negative Bacteria Causes Disease?

Gram-negative bacteria can cause disease by crossing the gastrointestinal lining and entering into the blood stream. Gram-negative bacterial cells can enter the human body through a number of different routes. For example, ingestion of contaminated water, inhalation from contaminated aerosols produced during respiration, and direct contact with skin or mucous membranes. Gram-negative bacteria have several virulence factors that aid them in invading the body. These gram-negative bacterial factors include an outer membrane, a variety of different toxins, lipopolysaccharides (LPS), and enzymes that invade tissue.


Gram Negative Bacteria Symptoms

Gram negative bacteria symptoms depend on the bacteria causing the disease. Some gram-negative bacterial infections include symptoms of gastrointestinal trouble including diarrhea, vomiting or abdominal pain. Other symptoms may include chills or fever, headache, and fatigue. Gram-negative bacteria may also result in respiratory problems such as pneumonia, sinusitis, sore throat and tonsillitis.


Gram Negative Diseases

Gram negative bacteria usually causes disease by releasing endotoxin into the blood stream and tissues of its host. Gram-negative bacteria also can cause diseases when it enters the body through skin wounds. Gram-negative skin infections are called cellulitis, which is an infection of the middle layer of skin or deep dermis. Gram-negative bacteria can also cause heart valve infections. One gram-negative bacteria, known as Aeromonas hydrophila, or Aeromonas, can cause food poisoning and gastroenteritis when ingested. Another gram-negative bacteria, Pseudomonas aeruginosa, can cause pneumonia, eye infections, ear infections, skin infections and soft tissue infections. Acinetobacter baumannii causes severe respiratory system diseases like pneumonia, meningitis (infection of the lining of brain), urinary tract infections, and bone and joint infections. Gram-negative bacteria can cause diseases because of its outer membrane that has lipopolysaccharide (LPS). Lipopolysaccharide or endotoxin is a toxic chemical that can cause sepsis, which is a Gram-negative bacteria blood poisoning. Gram negative sepsis is a medical emergency that can lead to death if not treated properly.


Treatment of Gram Negative Bacteria Infections

Gram-negative bacteria are treated with antibiotics that can penetrate their outer membrane. These medications function by passing through small channels in the outer membrane, known as porins. Gram-negative bacteria are also killed by using antibiotics that contain beta lactam ring, which is the main mode of action for amoxicillin. Ciprofloxacin is another effective antibiotic which works by inhibiting the enzymes that gram-negative bacterial cells need to reproduce. Antibiotic treatment should be continued until all symptoms of infection are gone or for at least ten days.


Gram Negative Bacteria Prevention

Gram-negative bacteria can be prevented by washing hands regularly, avoiding cuts or wounds, eating healthy (fruits and vegetables) to strengthen the immune system and practicing good oral hygiene (toothbrush, dental floss).

20th Jan 2022 Sean Grayson, PhD

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