What Do You Understand By The Term

Topics: Streptococcus, Streptococcus pyogenes, Bacteria Pages: 3 (605 words) Published: May 3, 2015
What do you understand by the term “Lancefield groups”?


In the early 1930’s Rebecca Lancefield recognized the importance of serological tests for the identification of organisms. The system is based on specific antibody agglutination reactions with cell wall carbohydrate antigens (C polysaccharides) extracted from the streptococci. Lancefield also showed that further sub division of group A into specific serological types was possible using type-specific M (protein) antigens. The groups are currently recognized from A to O, the common groups are: Pyogenes group: ABCFG (Beta haemolytic)

Viridans group (Alpha haemolytic)
Enterococci: D (Beta haemolytic, Alpha haemolytic or none.)

In 1918, Dr. Lancefield (above) joined the Rockefeller Institute for Medical Research, commencing her studies of the haemolytic streptococci, known then as Streptococcus haemolyticus. Following in the path of Oswald Avery, who had previously developed a serum (or precipitation) system for differentiating among types of pneumococci, Lancefield used similar methods to classify S. haemolyticus into groups according to antigens composed of carbohydrate. She also demonstrated that one of these groups, group A streptococci (S. pyogenes), was specific to humans and human disease, including pharyngitis ("strep throat"), scarlet fever, rheumatic fever, nephritis and impetigo. Group B streptococci were subsequently shown to be associated with neonatal disease. Dr. Lancefield further elaborated on the extensive variety of the group A streptococci, demonstrating that different serotypes were the result of antigenic variation of a cell surface protein, which she named M protein. In demonstrating the basis of antigenic specificity, she offered an explanation of M protein's role in the bacterium's mechanism of both surviving in the context of the human host and causing disease.

The coiled-coil dimeric nature of M protein and its relationship to the bacterial cell surface...
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