Tuberculosis is today one of the most spread infectious human diseases, being caused by a group of closely related species included in the Mycobacterium tuberculosis complex (MTBC). Molecular studies targeting tuberculosis affected human remains are important in order to understand the evolution of specific genomic sites related to virulence. The aim of this review is to describe several techniques that are useful for theconfirmation of pathogen persistence in the human archaeological remains. It also presents the genomic loci investigated in the field on molecular bioarchaeology for discrimination of MTBC species.
Keywords: tuberculosis, FT-IR, MALDI-TOF-MS, HPLC, ancient-DNA
World Health Organization (WHO) ranks tuberculosis as the second most dominant infectious disease, exceeded just by HIV/AIDS. Given the incidence of the disease today and the appearance of multi-drug-resistant strains, it is important to obtain informations about the conserved and variable genomic loci and about the mutation rate of the pathogen. For this reason, ancient cases of tuberculosis have to be investigated and the co-evolution of the pathogens and modern humans should be tracked.
Tuberculosis is caused by a group of closely related species with exclusivelly human hosts (Mycobacterium tuberculosis, M. africanum, M. canetti) or with a broader host spectrum: M. bovis (Brosch et al., 2002). These species are included in the M. tuberculosis complex (MTBC).
Comas et al. (2013) were able to infer the coalescence time of pathogenic species by analyzing the whole genomes of 259 MTBC strains. Thus, it was determined that MTBC accompanied humans in the Out-of-Africa migration and developed as a crowd disease during the Neolithic Demographic Transition (NDT). Evidence of spinal tuberculosis was found throughout the world, in Italy, Denmark and in the Middle East, dating from the Neolithic period (Smith, 2003). Osteological signs (resorbtion, growth) could not be interpreted as pathognomotic evidence for the disease. Ancient cases of tuberculosis should be confirmed by molecular methods. A number of techniques can be used for this purpose, targeting the ancient DNA (aDNA) of MTBC or the presence of mycolic acids in the human remains.
The aim of this review is to describe how a series of molecular techniques can be used for the diagnosis of ancient tuberculosis cases.
Detection of mycolic acids
The cell envelope of Mycobacterium species is composed of arabinogalactan-mycolate linked via a phosphodiester bond to the cell wall peptidoglycan. Mycolic acids are the dominant constituents of the cell envelope. They have structural and functional roles, defending the pathogen from noxious chemicals, oxidative stress or the host’s immune system. They are β-hydroxy fatty acids with a long α-alkyl side chain. Mycolic acids are classified in three structural classes: α-; methoxy- and keto-mycolic acids. They contain a carboxylic acid headgroup with two unequal...