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Gram Positive Bacteria: What They Are, What They Do and Common Examples

written by: Teresa Martin•edited by: dianahardin•updated: 4/13/2011

Gram positive bacteria are found on skin, in the mouth, in the intestinal tract and help keep the digestive system healthy.

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    Bacteria Basics

    Bacteria are one-celled organisms which move with a flagellum. There are many strains of bacteria able to live in a wide variety of conditions.Some strains can exist in extremely hot temperatures, some can exist in the presence of oxygen and some without oxygen. They can exist in freezing temperatures but do not grow in extreme cold, which is why food can be frozen for periods of time.

    Generally, bacteria are divided into either gram positive or gram negative types. The primary difference between gram positive and gram negative bacteria is the composition of the cell wall. Gram positive bacteria have more peptidoglycan in the cell wall - about 9 times as much. Peptidoglycan is a combination of amino acids and sugars. In the laboratory, when performing a gram stain, a gram positive bacteria will absorb the crystal violet stain and retain it through the decolorization process, giving the bacteria a purple appearance.

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    The Role of Bacteria in Our World

    Bacteria are everywhere and are important in causing decomposition. They help breakdown the food ingested, turn dead plants and animals into nutrition for the soil and are even used to breakdown oil from oil spills.

    A common gram positive bacteria, Lactobacillus, converts milk into products like cheese or yogurt. Lactobacillus is also important for the human digestive system to digest foods properly. This is why eating yogurt with active culture improve the digestion of foods.

    Bacteria have an important place in the world; however, some varieties of bacteria are disease producing. Some examples are given in the section below.

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    Disease Producing Bacteria

    Some common gram positive bacteria which affect our health can be found in the Streptococcus group. Streptococci cause conditions such as Strep throat, middle ear infections and rheumatic fever, to name a few. Varieties of Streptococci are distinguished by their interaction with blood agar. Some varieties cause hemolysis of the red blood cells, resulting in a clear area around the colonies. These are beta strep variety. An example of a beta strep is Streptococcus A, which is commonly found in strep throat.

    Streptococcus pneumonia is a bacteria which causes pneumonia. It's reaction with blood agar differs from the hemolytic action of group A. Strep pneumonia causes a greenish area around the colonies on a blood agar plate. The greenish tinge is due to the peroxidase present in Streptococcus pneumonia, which oxidizes red blood cells around the colony.

    Another common gram positive bacteria is Staphylococcus epidermidis. This bacteria is quite prolific on the skin and generally does not cause harm, except when a person is immunocompromised. Another variety, Staph aureus, causes acne and, if it gets under the skin, can result in the formation of an abcess. Because of treatment with antibiotics over the years, Staphylococcus aureus has modified itself genetically to be resistant to antibiotics. It is often acquired in hospitals and is one of the most predominant noscomial infections. This variation is known as MRSA, methicillin-resistant Staphylococcus aureus.