Bacteria are tiny organisms made up of a single cell that live on the surface of objects and grow in colonies. They are thought to have been on earth for almost 4 billion years. While many think of bacteria as something bad that causes illness, they are very useful in making soil, controlling bugs, degrading pollutants and making medicines.
Categories
Bacteria can be categorized based on their shape and whether the cell wall is thick or thin, which in turn affects how they respond to a Gram stain test. Thicker cell walls take up the dye in the Gram stain test better. The Gram stain is a test in which bacteria are washed with a purple dye and then treated with the alcohol and acetone. This means they can be gram positive or negative. In terms of shape, bacteria can be cocci or bacilli. While there are many types of bacteria, most fall into one of the four common types.
Gram-Positive Cocci
Cocci bacteria are spherical in shape. Gram positive means the bacteria do not lose their color when they are washed in alcohol and acetone during the Gram stain test. Staphylococcus is a form of gram-positive cocci. The most common species of Staphylococcus is Staphylococcus aureus, which affects the skin. These bacteria can also cause pneumonia and septicemia,a blood infection, but they normally respond well to antibiotics. This type of bacteria includes streptococcus, which most know as the cause of strep throat.
Gram-Negative Cocci
Gram-negative cocci do lose their color when washed in the Gram stain, are spherical, and have thinner cell walls than a gram-positive bacteria. Gram-negative bacteria also have an additional outer layer to the cell structure that makes them more virulent. Most gram-negative cocci fall into the Neisseria family. Neisseria bacteria are only found in humans and normally spread from person-to-person contact. This family of bacteria can cause a form of meningitis and gonorrhea. In children the gram-negative cocci Moraxella catarrhalis causes middle ear infections or swelling and sinusitis.
Gram-Positive Bacilli
Gram-positive bacilli are rod or cylindrical shaped and have thick cell walls. Some of the diseases caused by this type of bacteria are among the most dangerous known to humans. These diseases include anthrax and diphtheria. Anthrax and diphtheria are dangerous because of the powerful toxins produced by the bacteria. Species of Clostridium bacteria cause botulism, a bad form of food poisoning, and tetanus, a disease that affects muscles and nerves.
Gram-Negative Bacilli
Gram-negative bacilli can be thinner rods, curved, or have a thin needle shape. This type of bacteria is a large group with many subdivisions. Enterobacteria is a subdivision that includes those bacteria that cause food poisoning like E. coli, Salmonella, Shigella and Yersinia pestis. Gram-negative bacilli also cause urinary tract infections, diarrhea, peritonitis, and bloodstream infections. A species of the Gram-negative bacilli Vibrio is the cause of cholera. Vibrio is more comma-shaped than rod shaped. Gram-negative bacilli also cause pertussis, or whooping cough.
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