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Minimum evolution tree for the ply alleles. All alleles found in the pneumococcal reference set or other group 1 isolates (shown in boldface) were found to descend from a single node. The remainder were alleles from nontypeable isolates that clustered apart from group 1 in Fig. 1. The tree was generated using MEGA 2.1. All nucleotide differences were used in the analysis, and distances were corrected using the K2P model. The scale bar indicates substitutions per site.
