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List of Gram Negative Bacteria and Their Functions

written by: Nick Oza•edited by: dianahardin•updated: 5/18/2011

There are several types of Gram negative bacteria. In this article we will explore some Gram negative bacteria and review their structure, shape, function and medical significance.

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    What are Gram Negative Bacteria?

    Gram Negative Bacteria that Cause Legionellosis 

    During the process of Gram staining, Gram negative bacteria do not retain the crystal violet dye. Gram negative bacteria are colored red or pink, with the addition of a counter-stain. They have a cytoplasmic membrane and an outer membrane containing lipopolysaccharide. Additionally, there is an S-layer attached to the outer membrane. The lipopolysacchride in the outer membrane of Gram negative bacteria is an endotoxin, which triggers a response from the innate immune system. Inflammation is a common symptom of infection and can lead to toxicity.

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    Examples of Gram Negative Bacteria

    Gram negative bacteria cause infections, such as cholera, typhoid, meningitis and various kinds of gastrointestinal distresses. Secondary infections in hospitals are usually a result of an infection by a Gram negative bacteria. Here is a list of Gram negative bacteria, including a brief account of their structure, functions and medical significance.

    1. Salmonella - Salmonella are a genus of rod-shaped bacteria. They are non-spore forming enterobacteria with flagella. They oxidize and reduce organic substances and, in the process, produce hydrogen sulfide. Salmonella are found throughout the animal kingdom. They normally live within the intestinal tract of birds and other animals and can spread from animals to humans through the consumption of contaminated milk, eggs, poultry and beef. Nausea, vomiting, diarrhea and fever are common symptoms in humans who have Salmonella.

    2. Shigella - Shigella are a genus of rod-shaped Gram negative bacteria. Similar to Salmonella, they are non-spore forming. They only affect primates and not other mammals. Shigella are the cause of Shigellosis in humans. They also cause diarrhea and dysentery and can be spread from person-to person via contact and through ingestion of contaminated food and water. They destroy the cells that line the large intestine, resulting in ulceration and bloody diarrhea.

    3. Escherichia Coli - E.Coli, as they are commonly known, are a rod-shaped Gram negative bacteria. E.coli are non-sporulating. They can grow aerobically or anaerobically and cause the reduction of substrates, such as oxygen and nitrates. Although most strains of E.Coli are not harmful and are present in the gut of humans a few hours after childbirth, certain E.Coli strains can produce toxins that are lethal and can be dangerous. They can cause urinary tract infections, neonatal meningitis, food poisoning and serious complications, such as Hemolytic-uremic syndrome, in humans. The consumption of vegetables that are not properly washed and meat that has not been cooked thoroughly can result in E.Coli infections. E. Coli infections have also be known to occur from eating Hazelnuts.

    4. Helicobacter - Helicobacter are a genus of Gram negative bacteria shaped in the form of a helix. The species H.Pylori is of particular interest to bacteriologists and gastroenterologists, as it infects nearly 50% of humans. H.Pylori generally metabolize nitrogen. The lipopolysacchride that helicobacter contain has unique biological properties. Flagella help them to be motile and move fast. Certain species of helicobacter are known to cause peptic ulcers, gastritis and stomach cancer.

    5. Acetic acid bacteria - Acetic acid bacteria are rod-shaped Gram negative bacteria. These bacteria are so named as they oxidize ethanol to acetic acid during the process of fermentation, from which they derive their energy. They are present in nature, in flowers and fruits, and are an important part of the food industry. Wine fermentation also makes use of acetic acid bacteria, which are generally harmless to humans.

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    6. Legionella - Legionella bacteria are rod-shaped. The chemical composition of the bacteria's side-chains' cell wall, as well as different sugars, are responsible for classifying different types of Legionella. Legionella are most commonly known to cause Legionellosis, or Legionairre's disease, and Pontiac fever. Legionella are commonly found in public water sources, such as swimming pools and water fountains, central air-conditioning systems, household hot-water systems, ponds and creeks.

    7. Cyanobacteria - Also known as blue-green algae, cyanobacteria come in all shapes, from rods and cocci to spiriila. Cyanobacteria were responsible for turning the early atmosphere from an oxygen-depleted atmosphere to an oxygen-rich atmosphere. They derive most of their energy from photosynthesis. Cyanobacteria are commonly found in freshwater systems, marine environments and terrestrial sources. They can also be found in extreme environments, such as hot water springs. Some species of Cyanobacteria produce cyanotoxins, which can be harmful to humans and other species. In humans, Cyanobacteria can cause poisoning, and recent evidence suggests that they can also cause Amyotrophic Lateral Sclerosis (ALS).

    8. Neisseria gonorrhoeae - These are a motile, coffee-shaped bacteria, which have pili to adhere to surfaces. The pili in these bacteria can drag up to 100,000 times their own weight. N.Gonorrhoeae are primarily responsible for causing the sexually transmitted disease Gonorrhea. They are also known to cause conjunctivitis, orchitis and pharyngitis.

    9. Haemophilus Influenzae - These are rod-shaped bacteria. They are aerobic bacteria, but they can also exist as anaerobes. They are classified as encapsulated strains and unencapsulated strains. Capisular antigens define the classification of encapsulated strains. They are generally harmless to humans and exist within us under normal circumstances. When combined with a viral infection, however, they can cause pneumonia and meningitis in children, as well as sinusitis. In adults, they are known to cause eye infections and ear infections.

    10. Acinetobacter Baumanii - A. Baumanii are a pathogenic bacteria that are rod-shaped in their early stages but eventually take on a rounded shape. Part of the DNA within these bacteria is considered to be from other organisms, making the bacteria more virulent. They have no flagella and are sessile. In humans, they are primarily responsible for nosocomial infections, and rates of infections in hospitals are increasing steadily, due to A.Baumanii. They can affect those with a compromised immune system and are spread through catheters and breathing tubes. They are resistant to most antibiotics and have also been responsible for outbreaks amongst soldiers in the military, particularly during the Iraq war.

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    Importance of Gram Negative Bacteria

    Gram negative bacteria are important to the ecosystem of the planet. They are part of many animals and humans, and cyanobacteria are responsible for changing the Earth's atmosphere. Many Gram negative bacteria are also used for medical therapy and treatment of infections.

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    Image Credits: WikimediaCommons/CDC/WilliamCherry