pharyngitis (strep throat), impetigo, toxic shock syndrome, scarlet fever, rheumatic fever, and necrotizing
fasciitis. The M protein is an important virulence factor for Group A strep, helping these strains evade the
immune system. Changes in M proteins appear to alter the infectivity of a particular strain of Group A strep.Figure 3.31 Rebecca Lancefield (1895–1981) was the first to develop a method for distinguishing various
strains of β-hemolytic streptococci from each other based on their surface proteins.Flagella
Flagellaare structures used by cells to move in aqueous environments. Bacterial flagella act like propellers. They are
stiff spiral filaments composed of flagellin protein subunits that extend outward from the cell and spin in solution.
Thebasal bodyis the motor for the flagellum and is embedded in the plasma membrane (Figure 3.32). A hook
region connects the basal body to the filament. Gram-positive and gram-negative bacteria have different basal body
configurations due to differences in cell wall structure.
110 Chapter 3 | The Cell
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