Medical Definition of Group B
: the Lancefield group of usually beta-hemolytic streptococci that comprises all strains of a species of the genus Streptococcus (S. agalactiae) and that includes the causative agents of certain infections (as septicemia, pneumonia, and meningitis) especially of newborn infants—usually used attributively <affected with Group B strep>; compare group a
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Dictionary: Definition of "Group B"
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