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.

M Protein

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).

*Streptococcus pyogenes*

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

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An agglutination assay is a diagnostic technique that uses the clumping of bacteria to detect specific cell-surface antigens.

Agglutination Assay

https://openstax.org/details/books/microbiology/

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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Lancefield Classification

A hemagglutination assay is a direct diagnostic test that utilizes a patient's sample to detect specific viruses by observing their ability to agglutinate red blood cells, although it does not distinguish between infectious and noninfectious viral particles.

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