Array of M protein gene subtypes in 1064 recent invasive group a streptococcus isolates recovered from the active bacterial core surveillance

Using sequence analysis to detect variation within the hypervariable M protein N terminus, we found 41 emm types encompassing 81 subtypes, among 1064 consecutive invasive group A streptococcus isolates from a recent multistate, population- based surveillance. Seventeen of the 30 emm types represented by multiple isolates displayed multiple subtypes. Most subtypes differed from reference strain emm sequences as a result of single base substitutions or other alterations likely to be stably inherited. The Centers for Disease Control and Prevention database ( available at: http:// www. cdc. gov/ ncidod/ biotech/ strep/ strepblast. htm) currently contains 225 distinct emm types encompassing 450 subtypes. Although this subtyping scheme increases specificity, limited variation within individual types favors introduction of M protein type - specific vaccines.