Fig. 3. Combinations of 30-valent M protein and trivalent M-related protein (Mrp) (trMrp) antisera promote enhanced bactericidal killing against multiple Mrp-positive group A streptococci (GAS) emm types. Antisera to trMrp (blue column) or to 30-valent M protein vaccine (orange column) were used alone or in combination with each other (red column). Antisera were mixed with an equal volume of normal rabbit serum when used singly and equal volumes of each when combined. Bars represent the mean±standard error of mean of four independent experiments. The asterisk above the bars indicates that the combination of anti-trMrp and anti-30-valent sera was significantly different in killing (p<0.05) than either antisera alone.