Streptococcus pyogenes, a bacterium that grows in long chains, is present in between 5 and 15 percent of healthy people and poses no threat. However, under the right conditions it can cause a deadly infection and is often the cause of illnesses such as strep throat, toxic shock syndrome, scarlet fever, flesh-eating bacteria syndrome, impetigo and erysipelas.
Bacteria such as S. pyogenes can travel from one individual's respiratory system to another on droplets of moisture in the air. For example, when an individual with the bacterium sneezes another may breathe in droplets from the sneeze. Transmission can also occur through other means of sharing fluids, such as using an infected person's toothbrush or through an open wound. Once inside the body, the pathogen can travel through the bloodstream to other locations.
Entry into the Body
When bacteria live in or on our bodies without causing disease they are known as normal flora. S. pyogenes is often found as part of the normal flora in the respiratory tract. Normal flora can begin to cause disease if the body lets down its defenses, for example during another infection, or if the flora gain access to other areas of the body such as the blood.
Infection and Symptoms
Which diseases develop depends on where Streptococcus pyogenes takes up residence in the body. In the membranes of the brain, it can cause bacterial meningitis. In the ear, it can cause otitis (ear infection), while in the sinuses it can cause sinusitis. In the throat, or pharynx, it can cause pharyngitis—known as strep throat. In skin, it can cause several conditions, including impetigo or erysipelas, which bring on blister-like lesions on the skin. Scarlet fever includes a skin rash as well as sore throat, fever and typically a white coating on the tongue and throat. In the uterus, it can cause puerperal fever. This infection was once a common cause of death in women who had recently given birth. In the fascia surrounding the muscles, it can cause necrotizing fasciitis, also called flesh-eating bacteria syndrome.
Streptococcus pyogenes is sensitive to penicillin (no resistant strains are known). Consequently, individuals with an infection from S. pyogenes are typically treated with penicillin for at least 10 days. This kills the bacteria and cures the infection.
Serious complications can result if an infection is not treated. Acute rheumatic fever seems to occur after strep throat when antibodies from the immune system, which are meant to attack the strep infection, attack healthy body parts instead. Symptoms of rheumatic fever can include joint pain and inflammation of the heart. Glomerulonephritis involves inflammation of small blood vessels in the kidneys, which causes the body to retain fluid while blood or protein accumulates in urine. If untreated, glomerulonephritis can develop into end-stage kidney disease.