Diversity of fragments obtained after amplification following the nested-PCR method in a single closed tube. The sizes vary, including the expected 447 bp (lanes 4 and 7), 391 bp (lanes 1, 2, 3, and 9), and intermediate values (lanes 5, 6, 8, 10, and 11). Numbered lanes contain samples from the NCPPB collection (strain number and country of origin are given in parentheses): lane 1, 2292 (United States); lane 2, 2293 (United States); lane 3, 2950 (United States); lane 4, 311 (Canada); lane 5, 683 (United Kingdom); lane 6, 1734 (Egypt); lane 7, 1819 (United States); lane 8, 2080 (New Zealand); lane 9, 2791 (United States); lane 10, 3159 (The Netherlands); lane 11, 3548 (Turkey); lane M, marker (100-bp DNA ladder; Gibco BRL).