Streptococcus pyogenes

Streptococcus pyogenes (S. pyogenes) is a species of bacteria that is one of the most common disease-causing pathogens in humans. S. pyogenes is often present even in healthy individuals. It is estimated that as many as 15 percent of healthy individuals carry S. pyogenes asymptomatically, usually in the respiratory tract. Nevertheless, the S. pyogenes bacterium is a major cause of human disease. This is because the bacterium is capable of rapidly colonizing and multiplying within a host. Such rapid growth subsequently contributes to the development of an array of possible acute infections. While some of these possible infections, such as strep throat and impetigo, are relatively innocuous, some, like necrotizing fasciitis, can be life-threatening. Estimates suggest that S. pyogenes is responsible for causing about ten million minor throat and skin infections every year. Fortunately, S. pyogenes is highly sensitive to antibiotics, so most diseases it causes are easily treatable.

Background

The streptococcus family of bacteria was first described by German Austrian physician Theodor Billroth in the nineteenth century. Billroth made his historic breakthrough when he discovered S. pyogenes growing in his patients' infected wounds. S. pyogenes was formally named by German physician Michael Joseph Rossbach in 1884. The name pyogenes is taken from the Greek term for "pus-forming." American researcher Rebecca Lancefield officially classified S. pyogenes as a group A streptococcus in the 1930s. Group A was one of several alphabetically labeled groups into which different strains of streptococci are categorized. In recognition of her accomplishments, these groups are commonly referred to as the Lancefield groups. In addition to classifying S. pyogenes as a group A streptococcus, Lancefield also discovered the critical role that M protein, a special protein found in the cell walls of all group A streptococci, plays in S. pyogenes' ability to cause disease. Because there are variations in the chemical makeup of the cell walls of each strain, M proteins are also used to distinguish between the more than 120 different varieties of S. pyogenes.

In medicine, S. pyogenes initially came to be known among physicians as the cause of puerperal fever. Puerperal fever was a potentially life-threatening infection that often occurred in women shortly after childbirth. This disease was a common cause of childbirth-related deaths until nineteenth-century German Hungarian physician Ignaz Semmelweis discovered that it could be prevented if doctors simply washed their hands before performing vaginal examinations. Scarlet fever was another disease commonly caused by S. pyogenes infection before the advent of modern antibiotic therapy.

S. pyogenes is a gram-positive bacterium. Gram-positive bacteria have an especially thick cell wall made of a protein known as peptidoglycan. In gram-negative bacteria, peptidoglycan is found only in a small layer of the cell wall that is sandwiched between the inner and outer cell membranes. While gram-positive bacteria are often considered to be helpful and gram-negative bacteria are often considered harmful, neither of these assertions is entirely correct. Many gram-positive bacteria, including S. pyogenes, can cause disease. Similarly, some gram-negative bacteria can actually be beneficial for the human body.

Overview

S. pyogenes has a number of key characteristics that make it easy to identify. On a microscopic level, S. pyogenes appears to be a spherical bacterium that occurs in long, chain-like formations. In addition, S. pyogenes is a facultative anaerobic bacterium, which means that it can grow in an environment with or without oxygen. Studies have shown, in fact, that the growth of S. pyogenes is actually stimulated by the presence of carbon dioxide.

The virulence, or potential harmfulness, of S. pyogenes is determined by several different factors. Most importantly, S. pyogenes contains a special capsule that provides it with the ability to disguise itself from white blood cells. This means that it is difficult for the immune system to fight a S. pyogenes infection on its own. Further, the cell walls of S. pyogenes bacteria contain special proteins that allow it to adhere to the epithelial cells that make up skin. S. pyogenes bacteria are also capable of producing enzymes that help it to destroy tissue and spread. On top of all that, S. pyogenes bacteria is also able to produce mild toxins that cause rashes and other minor symptoms, as well as more dangerous toxins that can trigger organ failure.

S. pyogenes bacteria can cause a wide variety of diseases. Chief among these is streptococcal pharyngitis. Known more commonly as strep throat, streptococcal pharyngitis is the leading cause of bacterial sore throats and often results in a low-grade fever, a scratchy red throat with draining white patches, and swollen lymph nodes. Younger patients may also present with a headache or stomach ache. In some cases, strep throat may also be accompanied by rheumatic fever, an inflammatory condition that affects the skin, joints, heart, and nervous system.

Another disease caused by S. pyogenes bacteria is impetigo. Impetigo is a superficial skin infection that commonly occurs in children. The most common symptoms include the appearance of pustules and reddened skin around the arms, hands, or face. Impetigo may also lead to the appearance of itchy sores that ooze and form yellow crust.

S. pyogenes can also cause cellulitis, an infection that usually enters the body through cuts or scrapes in the skin. Cellulitis affects the deepest layers of the skin. It occurs most often on the face or legs. The skin around the infection site typically appears red and hot to the touch. Other symptoms of cellulitis include swollen skin, fever, chills, sweating, weakness, and shock.

Among the most serious conditions that S. pyogenes bacteria can cause is necrotizing fasciitis. Necrotizing fasciitis is a flesh-eating disease that occurs when bacteria enter the body and release a harmful toxin that destroys skin and other tissues. The damage caused by necrotizing fasciitis can spread quickly and may rapidly lead to death if it cannot be contained. S. pyogenes infections can also lead to toxic shock syndrome, a serious condition that occurs in response to an infection somewhere in the body. Toxic shock syndrome often results in fever, low blood pressure, kidney and liver failure, difficulty breathing, confusion, and bleeding problems. In severe cases, it may also lead to shock and death.

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