Streptococcus Pyogenes Diagnosis
Streptococcus pyogenes is one of the most common types of bacteria found on the skin. Many people carry these bacteria with no sign of disease. However, when the body's defenses are compromised, the bacteria have the potential to cause a variety of serious diseases, such as strep throat, impetigo, scarlet fever, rheumatic fever, necrotizing fasciitis and other skin infections. Because the bacteria cause such a wide variety of diseases, several different tests are used to diagnose Streptococcus pyogenes.
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Identification
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Streptococcus pyogenes is a facultative anaerobic gram-positive bacterium. It consists of long chains of round cells, about 0.6 to 1.0 micrometer in diameter. The bacteria is non-motile, meaning it does not move. It also does not produce spores. In order to grow, the bacteria require an enriched medium that contains blood.
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Common Diagnosis
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Because Streptococcus pyogenes is responsible for a variety of diseases, various steps are taken to diagnose the bacteria. Strep throat is commonly diagnosed through a throat culture. Once the throat has been swabbed, the bacteria are smeared onto a specific blood culture plate that allows the bacteria to grow. Results are typically available within 24 to 48 hours. If the bacteria grow, the test is positive for strep throat. If the bacteria do not grow, the test is negative.
The blood culture test should show beta-hemolysis, which occurs when the bacteria eats through the blood agar. If you hold up the blood agar plate to a source of light, you should notice that the bacteria have eaten almost completely through the blood agar. A gram stain may also be done on the bacteria. The gram stain should show gram-positive bacterium in a streptococcus arrangement; essentially, the stain should show purple circular cells in long chains.
Rapid Diagnosis
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A rapid strep test has also been developed to diagnose strep throat within just a few minutes. A rapid strep test also a throat culture. A cotton swab is rubbed over the tonsils and throat, and then placed in a specialized container. These cotton swabs are designed to respond only to the presence of Streptococcus pyogenes, which is responsible for strep throat. A positive test will indicate the presence of the bacteria.
Visual Diagnosis
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Scarlet fever and impetigo can both be diagnosed through a visual examination, since their symptoms are easily recognizable. Scarlet fever is characterized by a bright red rash that begins on the chest and may spread out to the rest of the body. The rash looks like tiny red pinpoints on the skin and has a rough texture similar to sandpaper. Impetigo starts quite simply as a red sore, but forms into a crusty sore after a few days. Necrotizing fasciitis is first diagnosed through a visual examination, but further medical tests are often necessary. Necrotizing fasciitis causes extensive tissue damage and is fatal in 30 to 40 percent of all cases.
Treatment
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Because the Streptococcus pyogenes bacteria do not form spores, they can be easily destroyed. Diseases caused by these bacteria typically respond well to antibiotics; penicillin is the most commonly prescribed medication to treat diseases caused by Streptococcus pyogenes. However, necrotizing fasciitis often involves the surgical removal of all infected tissue, since the bacteria spreads rather quickly.
References
Resources
- Photo Credit "Bacteria" is Copyrighted by Flickr user: kaibara87 (Umberto Salvagnin) under the Creative Commons Attribution license.
