Polymorphisms of pepA and PPE18 genes in clinical isolates of Mycobacterium tuberculosis in children

Abstract

Objective To sequence the antigen-encoding genes pepA and PPE18 from clinical isolates of Mycobacterium tuberculosis (MTB) and analyze their polymorphisms. Methods A total of 168 clinical isolates of MTB collected from the Department of Infection of the Children's Hospital of Chongqing Medical University from December 2006 to December 2013 were selected, corresponding to 168 cases with tuberculosis in children aged 7.8±5.7 years, with 87 males and 81 females.The target genes, pepA and PPE18, were amplified by PCR and sequenced respectively.The results of sequences were compared with the gene sequences of H37Rv, the standard strain of MTB, and the sequences of the epitopes searched from the immune epitope database (IEDB) to analyze the mutation characteristics of the gene sequences of pepA and PPE18. Results Among the 168 strains, mutations in PPE18 were found in 117(69.64%) strains and 10 of the 17 T cell antigenic epitopes of the PPE18 were altered.Six (9.84%) TB strains out of 168 clinical TB isolates showed polymorphisms in pepA gene and did not result in alteration of T cell antigenic epitopes. Conclusion PepA gene sequence is conservative, and PPE18 is highly polymorphic, which is predicted to affect the immune function of the M72 vaccine composed of pepA and PPE18 proteins, thus affecting the immunization effectiveness of the M72 vaccine.

Keywords

• mycobacterium tuberculosis
• pepa
• ppe18
• m72
• gene polymorphism