The bacterium *Streptococcus pyogenes* is a Lancefield group A, $$\beta$$-hemolytic species classified as a pyogenic pathogen due to the pus production associated with its infections. It is the most common cause of bacterial pharyngitis (strep throat) and can also lead to skin infections ranging from mild impetigo to life-threatening conditions like necrotizing fasciitis (flesh-eating disease).

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An infection that develops in the dermis or hypodermis can cause cellulitis, which presents as a reddened area of the skin that is warm to the touch and painful.

Cellulitis

Lancefield classification is a method for serotyping various $$\beta$$-hemolytic strains of *Streptococcus* species based on their cell-surface antigens using an agglutination assay.

Lancefield Classification

Streptococcus is a genus of low G+C gram-positive bacteria and a cellular arrangement of spherical cells forming chains. It includes many pathogens responsible for human diseases such as pharyngitis (strep throat), scarlet fever, rheumatic fever, glomerulonephritis, pneumonia, and other respiratory infections.

Streptococcus

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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Localized inflammation of the dermis and hypodermis, red warm skin and painful to the touch.

Signs and Symptoms of Cellulitis

*Streptococcus pyogenes*

The M protein is a cell-surface protein and virulence factor found on Group A streptococci (*Streptococcus pyogenes*) that helps the bacteria evade the host immune system. Variations in M proteins allow differentiation of more than 80 strains of Group A strep, and changes in this protein can alter the infectivity of a strain.

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