Mycobacterium tuberculosisproduces pili during human infection

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Abstract
Mycobacterium tuberculosisis responsible for nearly 3 million human deaths worldwide every year. Understanding the mechanisms and bacterial factors responsible for the ability ofM. tuberculosisto cause disease in humans is critical for the development of improved treatment strategies. Many bacterial pathogens use pili as adherence factors to colonize the host. We discovered thatM. tuberculosisproduces fine (2- to 3-nm-wide), aggregative, flexible pili that are recognized by IgG antibodies contained in sera obtained from patients with active tuberculosis, indicating that the bacilli produce pili or pili-associated antigen during human infection. PurifiedM. tuberculosispili (MTP) are composed of low-molecular-weight protein subunits encoded by the predictedM. tuberculosisH37Rv ORF, designated Rv3312A. MTP bind to the extracellular matrix protein lamininin vitro, suggesting that MTP possess adhesive properties. Isogenicmtpmutants lost the ability to produce Mtpin vitroand demonstrated decreased laminin-binding capabilities. MTP shares morphological, biochemical, and functional properties attributed to bacterial pili, especially with curli amyloid fibers. Thus, we propose that MTP are previously unidentified host-colonization factors ofM. tuberculosis.