Immunoscreening of the M. tuberculosis F15/LAM4/KZN secretome library against TB patients' sera identifies unique active- and latent-TB specific biomarkers.

Tuberculosis (TB) protein biomarkers are urgently needed for the development of point-of-care diagnostics, new drugs and vaccines. Mycobacterium tuberculosis extracellular and secreted proteins play an important role in host-pathogen interactions. Antibodies produced against M. tuberculosis proteins before the onset of clinical symptoms can be used in proteomic studies to identify their target proteins. In this study, M. tuberculosis F15/LAM4/KZN strain phage secretome library was screened against immobilized polyclonal sera from active TB patients (n = 20), TST positive individuals (n = 15) and M. tuberculosis uninfected individuals (n = 20) to select and identify proteins recognized by patients' antibodies. DNA sequence analysis from randomly selected latent TB and active TB specific phage clones revealed 118 and 96 ORFs, respectively. Proteins essential for growth, virulence and metabolic pathways were identified using different TB databases. The identified active TB specific biomarkers included five proteins, namely, TrpG, Alr, TreY, BfrA and EspR, with no human homologs, whilst latent TB specific biomarkers included NarG, PonA1, PonA2 and HspR. Future studies will assess potential applications of identified protein biomarkers as TB drug or vaccine candidates/targets and diagnostic markers with the ability to discriminate LTBI from active TB.