Streptococcus, commonly known as strep, refers to a group of bacteria that can cause various infections in humans. When people discuss “strep throat,” they are referring to an infection caused by a specific type of this bacterium. The body’s ability to defend itself against these infections is known as immunity.
Understanding Strep Bacteria and Its Types
The genus Streptococcus encompasses numerous bacterial species. Group A Streptococcus (GAS), specifically Streptococcus pyogenes, is the most well-known cause of “strep throat.” This bacterium can also lead to other infections, ranging from skin infections like impetigo to more severe conditions. A defining feature of GAS is its M protein, a molecule on the bacterial surface. Variations in this M protein lead to the classification of GAS into over 200 distinct “serotypes” or “strains,” which are genetically different versions of the bacterium.
How the Immune System Responds to Strep
When the body encounters Streptococcus pyogenes, the immune system responds. Immune cells recognize specific bacterial components, such as the M protein. This recognition triggers the production of specialized proteins called antibodies. Antibodies bind to bacterial components, marking them for destruction.
Following a successful infection, the immune system develops memory cells. These cells “remember” the specific bacterial strain and can mount a faster, more effective antibody response if the same strain is encountered again. However, this acquired immunity is serotype-specific, meaning antibodies developed against one M protein serotype may not protect against a different serotype.
Why Strep Reinfections Occur
The recurring nature of strep throat infections directly relates to the diversity of Streptococcus pyogenes strains. An infection with one strain only grants immunity to that specific strain. For example, if someone develops antibodies against an M protein type 1 strain, those antibodies will protect against future infections by that same type.
However, if that individual is later exposed to a different serotype, such as M protein type 2, their existing antibodies may not recognize it effectively. This leaves the person susceptible to a new infection. This explains why someone can experience multiple episodes of strep throat throughout their life, each potentially caused by a different strain of the bacterium.
Preventing Strep and Its Complications
Preventing strep infections involves basic hygiene practices to limit bacterial spread. Regular handwashing, especially after coughing or sneezing and before eating, can reduce transmission. Avoiding the sharing of eating utensils, drinks, and food also helps minimize exposure to the bacteria.
Early diagnosis and complete antibiotic treatment of strep throat are important to prevent serious complications. Untreated strep throat can lead to conditions such as acute rheumatic fever, which can affect the heart, joints, and brain, or post-streptococcal glomerulonephritis, a kidney disorder. While these complications are less common in regions with access to antibiotics, they remain a concern globally. Currently, a widely available vaccine for Group A Strep is not available, though research continues to develop a vaccine that could offer broad protection against the many different strains.