Genetic variability of PE_PGRS17 and PE_PGRS18 genes throughout a worldwide collection of tubercle bacilli isolates. The sequenced region encompasses nucleotides 31 to 712 for both genes (numbering according to the reference strain H37Rv). Sequences of both genes were concatenated and, for MTBC strains, each unique sequence was assigned a type number (T1 to T26). Yellow boxes indicate that the sequence at this site is identical to that of the reference strain M. tuberculosis H37Rv. Blue and orange backgrounds correspond to genetic variations (in comparison to H37Rv) within PE_PGRS17 and PE_PGRS18 sequenced regions, respectively. White background indicates no sequence available. STB: Smooth tubercle bacillus. I1: A trinucleotide (GCC) insertion immediately after position 90. I2; A 1-nucleotide (A) frameshift insertion immediately after position 270. Δ1: A 114-nucleotide in frame deletion from positions 512 to 625. Δ2: A 9-nucleotide in frame deletion from positions 631 to 639.