Pyogenes Description and Significance Streptococcus pyogenes is a gram-positive bacterium that usually grows in pairs or chains. It has been classified as a beta-hemolytic streptococcus because when cultured on a blood agar plate all the red blood cells are ruptured by the bacteria 1. Furthermore, it has been classified using Lancefield serotyping as group A, because it displays antigen A on its cell wall. Therefore, this bacterium is commonly called the beta-hemolytic group A streptococcus, or GAS.
Streptococcus pyogenes, other Streptococci, and Enterococcus Clinical Manifestations Acute Streptococcus pyogenes infections may take the form of pharyngitis, scarlet fever rashimpetigo, cellulitis, or erysipelas. Invasive infections can result in necrotizing fasciitis, myositis and streptococcal toxic shock syndrome.
Patients may also develop immune-mediated Streptococcus pyogenes essay such as acute rheumatic fever and acute glomerulonephritis. S agalactiae may cause meningitis, neonatal sepsis, and pneumonia in neonates; adults may experience vaginitis, puerperal fever, urinary tract infection, skin infection, and endocarditis.
Viridans streptococci can cause endocarditis, and Enterococcus is associated with urinary tract and biliary tract infections. Anaerobic streptococci participate in mixed infections of the abdomen, pelvis, brain, and lungs. Structure Streptococci are Gram-positive, nonmotile, nonsporeforming, catalase-negative cocci that occur in pairs or chains.
Older cultures may lose their Gram-positive character. Most streptococci are facultative anaerobes, and some are obligate strict anaerobes. Most require enriched media blood agar.
Group A streptococci have a hyaluronic acid capsule. Classification and Antigenic Types Streptococci are classified on the basis of colony morphology, hemolysis, biochemical reactions, and most definitively serologic specificity.
They are divided into three groups by the type of hemolysis on blood agar: Serologic grouping is based on antigenic differences in cell wall carbohydrates groups A to Vin cell wall pili-associated protein, and in the polysaccharide capsule in group B streptococci. Pathogenesis Streptococci are members of the normal flora.
Virulence factors of group A streptococci include 1 M protein and lipoteichoic acid for attachment; 2 a hyaluronic acid capsule that inhibits phagocytosis; 3 other extracellular products, such as pyrogenic erythrogenic toxin, which causes the rash of scarlet fever; and 4 streptokinase, streptodornase DNase Band streptolysins.
Some strains are nephritogenic. Immune-mediated sequelae do not reflect dissemination of bacteria. Nongroup A strains have no defined virulence factors. Host Defenses Antibody to M protein gives type-specific immunity to group A streptococci.
Antibody to erythrogenic toxin prevents the rash of scarlet fever. Immune mechanisms are important in the pathogenesis of acute rheumatic fever. Maternal IgG protects the neonate against group B streptococci.
The incidence of both respiratory and skin infections peaks in childhood. Infection can be transmitted by asymptomatic carriers. Acute rheumatic fever was previously common among the poor; susceptibility may be partly genetic.
Group B streptococci are common in the normal vaginal flora and occasionally cause invasive neonatal infection. Diagnosis Diagnosis is based on cultures from clinical specimens. Serologic methods can detect group A or B antigen; definitive antigen identification is by the precipitin test.
Acute glomerulonephritis and acute rheumatic fever are identified by anti-streptococcal antibody titers.
In addition, acute rheumatic fever is diagnosed by clinical criteria. Control Prompt penicillin treatment of streptococcal pharyngitis reduces the antigenic stimulus and therefore prevents glomerulonephritis and acute rheumatic fever.
Vancomycin resistance among the enterococci is an emerging microbial threat. Vaccines are under development. Streptococcus pneumoniae S pneumoniae causes pneumonia, meningitis, and sometimes occult bacteremia. Autolysis is enhanced by adding bile salts. Classification and Antigenic Types There are more than 85 antigenic types of S pneumoniaewhich are determined by capsule antigens.
There is no Lancefield group antigen. Pathogenesis S pneumoniae is a normal member of the respiratory tract flora; invasion results in pneumonia.
The best defined virulence factor is the polysaccharide capsule, which protects the bacterium against phagocytosis.Resistance, Infections, and Defenses of Streptococcus pyogenes Streptococcus pyogenes was the bacteria that used to be the cause of numerous cases of human sicknesses and deaths.
S pyogenes (a group A streptococcus) is the leading cause of uncomplicated bacterial pharyngitis and tonsillitis. Indeed, only group A streptococci are sought routinely in cases of pharyngitis, although groups B, C, and G are sometimes identified.
Streptococcus Pyogenes Custom Essay [meteor_slideshow slideshow=”arp1″] Abstract Introduction to contain information about the pathogen, the diseases caused, and clinical and economic significance Differentiating diagnostic characteristics [physiological and biochemical]. A = Streptococcus grupobittia.com further confirm that sample A is Streptococcus pyogenes you can undergo a PYR test.
The PYR test is a rapid colorimetric method which tests for the presence of the enzyme pyrrolidonyl aminopeptidase present in the microorganism. Discussion: Streptococcus Pyogenes a Group A Streptococcus is a Gram-positive, non-motile, non-spore forming coccus that occurs in chains and are round cocci.
The metabolism of Streptococcus Pyogenes is fermentative and is a catalase-negative facultative anaerobe, and requires enriched medium containing blood in order to grow. 3/5(2).
streptococcus pyogenes Essay Streptococcus pyogenes Research paper MCB C March 17, Nature of Causative Organism Streptococcus pyogenes, a group A streptococci, is a gram-positive, non-spore forming bacteria that can be seen as oval cocci chain forming shapes less than 2 micrometers in diameter under the microscope.