Streptococci are gram-positive aerobic bacteria that can cause many illnesses, incl. Pharyngitis, pneumonia, wound and skin infections, sepsis and endocarditis. The symptoms vary depending on the infected organ. Consequences of infections by group A beta-hemolytic streptococci can be rheumatic fever and glomerulonephritis. Most strains are also sensitive to penicillin, but recently macrolide-resistant strains have emerged.
(See also Pneumococcal infections Pneumococcal infections Streptococcus pneumoniae (Pneumococci) are gram-positive, alpha-hemolytic, aerobic, encapsulated diplococci In the U.S., pneumococcal infections annually cause ca. 7. Learn More ; Rheumatic Fever Rheumatic fever is a nonpurulent, acute inflammation, a complication of infection with group A pharyngeal streptococcus (SGA), which is a combination of arthritis, carditis. Learn more ; and tonsillopharyngitis Tonsillopharyngitis is an acute pharyngeal and/or palatine tonsillar infection. Symptoms may include sore throat, dysphagia, cervical lymphadenopathy, and fever. Learn More )
Classification of streptococci
When grown on sheep blood agar, three different types of streptococci can be primarily distinguished:
Beta-hemolytic streptococci produce zones of clear hemolysis around each colony.
Alpha-hemolytic streptococci (often called viridans streptococci) are surrounded by a greenish discolored zone due to only partial hemolysis.
Gamma-hemolytic streptococci are not hemolytic.
The broader classification is based on carbohydrates in the cell wall and divides streptococci into Lancefield groups A through H and K through T (see table: Lancefield classification Lancefield classification Streptococci are gram-positive aerobic bacteria that can cause many diseases, incl. pharyngitis, pneumonia, wound and skin infections, sepsis, and endocarditis. The symptoms. Learn more ). Viridans streptococci form a separate group that is difficult to classify. In the Lancefield classification, enterococci were initially classified among group D streptococci. More recently, enterococcal enterococcal infections Enterococci are gram-positive, facultative aerobic organisms. Enterococcus faecalis and E. faecium cause a number of infections such as endocarditis, urinary tract infections. Learn More classified as a separate genus, but they express Lancefield group D antigens. Some streptococci such as Streptococcus pneumoniae do not express Lancefield antigens.
Many streptococci produce virulence factors, z. B. Streptolysins, DNAses, and hyaluronidase, which contribute to tie destruction and spread of infection. Some strains release exotoxins that activate certain T cells and trigger the release of cytokines, including tumor necrosis factor-alpha, interleukins, and other immune modulators. These cytokines activate the complement, coagulation, and fibrinolysis systems, leading to shock, organ failure, and death.
Diseases caused by streptococci
The most clinically significant streptococcal species is S. pyogenic Which is beta-hemolytic and belongs to Lancefield group A, which is why they are called group A-β-hemolytic streptococci (GABHS).
The Most common acute illness due to GABHS Are
Furthermore, delayed nonpurulent complications (rheumatic fever Rheumatic fever is a nonpurulent acute inflammation, a complication of infection with group A pharyngeal streptococci (SGA), which is a combination of arthritis, carditis. Learn more , Acute glomerulonephritis Postinfective glomerulonephritis Postinfective glomerulonephritis occurs after infection usually with a nephritogenic strain of beta-hemolytic streptococci (group A). The diagnosis is made by history. Learn More ).
Diseases caused by other streptococcal species are less common and usually manifest as soft tie infections or endocarditis (see table: Lancefield classification Lancefield classification Streptococci are gram-positive aerobic bacteria that can cause many diseases, incl. Pharyngitis, pneumonia, wound and skin infections, sepsis and endocarditis. The symptoms. Learn More ). Some non-GABHS infections occur predominantly in certain populations (z. B. Group B streptococcus in newborns and women).
GABHS can spread through affected ties and along lymphatics (lymphangitis) to regional lymph nodes (lymphadenitis). GABHS can also cause local purulent complications such as z. B. Peritonsillar abscess, otitis media, sinusitis, and bacteremia. Pus formation depends on the severity of the infection. The susceptibility of the tie depends.
Other serious GABHS infections include sepsis, puerperal sepsis, endocarditis, pneumonia, and empyema.
Streptococcal pharyngitis is most commonly caused by GABHS. About 20% of patients present with sore throat, fever, a dusky red pharynx, and a purulent tonsillar exudate. The remaining patients have less prominent symptoms, and the clinical picture resembles that of viral pharyngitis. The cervical and submaxillary lymph nodes may enlarge and swell. Streptococcal pharyngitis can lead to peritonsillar abscess Peritonsillar abscess and peritonsillitis Acute throat infections such as peritonsillar abscess and peritonsillitis are particularly common in adolescents and young adults. Its symptoms are severe sore throat. Learn more lead. Cough, laryngitis, and nasal congestion are not characteristic of streptococcal pharyngeal infection; their presence indicates another cause (usually viral or allergic).
Up to 20% of all people may have an asymptomatic carrier status.
Scarlet fever is uncommon today, but outbreaks still occur. Transmission occurs in environments with close human contact. (z. B. in schools or day care centers).
Scarlet fever, a disease that occurs predominantly in childhood, usually follows a throat streptococcal infection; less commonly, streptococcal infections elsewhere (e.g. B. of the skin). Scarlet fever is caused by group A streptococci, which produce an erythrogenic toxin that causes a diffuse, pinkish-red rash that fades under prere.
The rash is best observed on the abdomen or lateral thorax, as dark red lines in skin folds (pastia lines) or as circumoral pallor. The rash consists of characteristic, numerous, small (1-2 mm) papular elevations that give the skin a quality of sandpaper. The upper layer of previously red skin often scales after the fever disappears. The rash usually lasts 2-5 days.
Strawberry tongue (inflamed papillae protruding from a bright red layer) may also occur and must be distinguished from the in toxic shock syndrome Toxic shock syndrome (TSS) Toxic shock syndrome is caused by staphylococcal or streptococcal exotoxins. Symptoms consist of high fever, drop in blood prere, diffuse erythematous skin rashesä. Learn more and Kawasaki disease Kawasaki syndrome Kawasaki syndrome, or mucocutaneous lymph node syndrome, is a vasculitis that sometimes involves the coronary arteries and occurs in infants and children between 1 and 8 years of age. Learn more become differentiated.
Other symptoms resemble those of streptococcal pharyngitis, and the course and treatment of scarlet fever are the same as those of other group A infections.
Streptococcal infections of the skin
The Impetigo is a superficial skin infection that causes crusting and blistering.
The Erysipelas Erysipelas is a form of superficial cellulitis involving the dermal lymphatic system. The diagnosis is made clinically. Treatment consists in the administration of oral. Learn more Is a superficial cellulitis that also affects the lymphatic vessels. Patients have shiny, bright red, raised, indurated lesions with sharp borders. It is most commonly caused by GABHS, but other streptococci and nonstreptococci are sometimes involved.
A Cellulitis Cellulitis is an acute bacterial infection of the skin and subcutaneous tie, usually caused by staphylococci or streptococci. Symptoms and signs include pain, warmth, rapidly developing. Learn more affects the deeper layers of the skin and can spread rapidly due to the numerous lytic enzymes and toxins produced mostly by group A streptococci.
A necrotizing fasciitis Necrotizing soft tie infections A necrotizing soft tie infection typically results from mixed aerobic-anaerobic flora leading to subcutaneous tie necrosis, usually including fascia. This. Learn more , caused by S. pyogenic, is a severe dermal (and sometimes muscular) infection that spreads along fascial layers. Vaccination occurs through the skin or intestine.
Necrotizing fasciitis also occurs with i.v. substance abuse before.
Originally known as streptococcal gangrene and referred to by the media as flesh-eating bacteria, the same syndrome can also be polymicrobial and involve a variety of aerobic and anaerobic flora, incl. Clostridium perfringens. Polymicrobial infection is likely if the source is the intestine (z. B. after intestinal surgery, intestinal perforation, diverticulitis or appendicitis).
Symptoms of necrotizing fasciitis begin with fever and exquisite local pain out of proportion to physical findings; pain increases rapidly with time and is often the first (and sometimes only) manifestation. Diffuse or local erythema may be present. Thrombosis of small vessels causes ischemic necrosis, which in turn leads to rapid spread with disproportionately severe toxicity. In 20-40% of cases, the disease spreads to adjacent muscles. Shock often develops. a renal dysfunction. The lethality is high even with therapy.
Toxic shock syndrome caused by streptococcus
Toxin-producing GABHS strains can cause Streptococcal toxic shock syndrome LLLToxic shock caused by streptococci Toxic shock syndrome is caused by staphylococcal or streptococcal exotoxins. Symptoms consist of high fever, drop in blood prere, diffuse erythematous skin rashesä. Learn more , which is similar to S. aureus caused resembles. Patients are usually otherwise healthy children or adults with skin and soft tie infections.
Late complications of streptococcal infection
The mechanism by which certain GABHS strains cause delayed complications is unclear, but may involve cross-reactivity of streptococcal antibodies to host ties.
The rheumatic fever Rheumatic fever is a nonpurulent, acute inflammation, a complication of infection with group A pharyngeal streptococci (SGA), which is a combination of arthritis, carditis. Learn more is an inflammatory disease and occurs in 3% of patients a few weeks after untreated GABHS pharyngitis. It has become much less common in developed countries, but is still widespread in developing countries. The diagnosis of a first episode is based on the combination of arthritis, carditis, chorea, specific skin manifestations, and results of laboratory tests (Jones Criteria-see table: Modified Jones Criteria for First Episode of Acute Rheumatic Fever (ARF)* Rheumatic fever is a nonpurulent, acute inflammation, a complication of a group A pharyngeal streptococcal infection (SGA), which is a combination of arthritis, carditis. Learn more ).
One of the most important reasons for treating GABHS pharyngitis of streptococcal pharyngitis is to prevent the rheumatic fever.
A Acute poststreptococcal glomerulonephritis Rapidly progressive glomerulo- nephritis (RPGN) Rapidly progressive glomerulonephritis (RPGN) is an acute nephritic syndrome of microscopic glomerular crescent formation with progression to renal failure within. Learn more manifests as acute nephritic syndrome following pharyngitis or skin infection by certain limited nephritogenic GABHS strains (z. B. M protein serotypes 12 and 49) After pharyngitis or skin infection with one of these strains, approximately 10-15% of patients develop acute glomerulonephritis. It is most common among children, ca. 1-3 weeks after infection. Complete recovery without permanent kidney damage occurs in nearly all children, somewhat less frequently in adults. Antibiotic treatment of GABHS infection has only a small effect on the development of glomerulonephritis.
The PANDAS syndrome Symptoms and complaints Tics are defined as repetitive, sudden, rapid, nonrhythmic muscle movements, including noises or sounds. Tourette's syndrome is diagnosed at. Learn more (Pediatric autoimmune neuropsychiatric disorder associated with group A streptococcus) refers to a subset of obsessive-compulsive or tic disorders in children thought to be exacerbated by GABHS infection.
Certain forms of Psoriasis Psoriasis is an inflammatory disease usually associated with sharply defined erythematous papules and plaques covered with silvery scales. Multiple factors. Learn more (z. B. Guttate) may also be associated with beta-hemolytic streptococcal infections.
Sometimes rapid antigen tests or antibody titers
Streptococci can be easily identified by culture on sheep blood agar.
Rapid antigen tests, that allow detection of GABHS directly from throat swabs are available (d.h. for point-of-care use). Many tests use enzyme immunoassays, but recently tests that use optical immunoassays have become available. These rapid tests are highly specific (> 95%), but sensitivity varies considerably (55-80% or 90% with the newer optical immunoassay tests). Thus, positive results can confirm the diagnosis, but negative results should be confirmed by culture, at least in children. Because streptococcal pharyngitis is less common in adults and adults are unlikely to have poststreptococcal complications, many physicians do not confirm a negative rapid screening result in adults by culture unless the use of a macrolide is being considered; in such cases, sensitivity testing is performed to determine macrolide resistance.
The detection of Antibodies against streptococci in serum during convalescence provides only indirect evidence of infection. Antistreptococcal antibody tests are not useful for diagnosing acute GABHS infection because the antibody does not develop until several weeks after the onset of GABHS infection, and a single high antibody titer tends to reflect a long precursor infection. Antibody detection is very helpful in the diagnosis of poststreptococcal diseases such as z. B. rheumatic fever. Glomerulonephritis. rheumatic fever and glomerulonephritis.
Antistreptolysi- O (ASO) and antidesoxyribonuclease B (anti-DNase B) titers begin to rise about 1 week after GABHS infection and peak about 1 to 2 minutes after infection. Both titers may be elevated for several months even after uncomplicated infections. Titers are measured in the acute phase and convalescence phase 2 to 4 weeks later; a positive result is defined as a ≥ 2-fold increase in the titer. A single titer greater than the upper limit of normal suggests a preceding streptococcal infection or high streptococcal endemicity in the community. ASO titer only rises in 75 to 80% of infections. For completeness, any of the other available tests (antihyaluronidase, antinicotinamide adenine dinucleotidase, antistreptokinase) can also be used in difficult cases.
Penicillin administration within the first 5 days of symptomatic streptococcal pharyngitis can delay the onset of the ASO antibody response and reduce its severity.
Patients with streptococcal pyoderma usually do not have a significant ASO response, but may produce antibodies to other antigens (z. B. anti-DNAse, antihyaluronidase).