Year: 2020
Type: dissertation
Abstract: CFP-10) by non-tuberculous mycobacterial species (Master Thesis Agnes Bouw)-3 - ABSTRACTIntroduction: Tuberculosis (TB) is a widespread chronic infectious granulomatous disease of many animal species as well as humans that is caused by mycobacteria.Several TB diagnostics use the immunogenic proteins Early Secreted Antigenic Target-6 (ESAT-6) and Culture Filtrate Protein 10 (CFP-10) as diagnostic markers.These proteins are thought to be important for virulence and specific for pathogenic mycobacterial species such as members of the Mycobacterium tuberculosis complex (MTBC).However, an increasingly number of non-tuberculous mycobacteria (NTM) species, most of wich are considered to be only environmental contaminants or commensals, have been found to contain gene orthologues of esxA and esxB genes coding for ESAT-6 and CFP-10 respectively.If these NTM species express ESAT-6 and CFP-10, cross-reactive immune responses between MTBC and NTM species may occur.NTM may therefore interfere with diagnostic tests for and vaccination against TB.The research aim was to investigate whether M. moriokaense, M. malmesburri sp.nov., M. vaccae/M.vanbaalenii, M. madagascariense, M. acapulcensis, M. elephantis, M. chitae, M. confluentis, M. paraffinicum, M. neonarum, M. engbackii, M. parafortuitum, M. septicum/peregrinum, M. smegmatis, M. fortuitum, M. komanii sp.nov.and M. nonchromogenicum possess orthologue esxA and/or esxB genes. Materials & methods:Polymerase chain reactions (PCR) were performed using M. bovis derived primers for the esxA and esxB genes.Amplification products sized approximately 300 basepairs were extracted and submitted for sequencing.BLAST (Basic Local Alignment Search Tool) searches were performed on the sequeces to identify if sequences were coding for ESAT-6 or CFP-10.EsxA and esxB sequences next to 16S rRNA sequences of NTM were used for phylogenetic analysis.The three phylogentic trees were compared by similarity and a consensus tree was created.Results: EsxB orthologues were detected in M. engbackii isolates and in M. paraffinicum.The esxB orthologues were 86-88% similar at nucleotide level to the genes coding for CFP-10 in other NTM-like M. szulgai, M. marinum, M. pseudohottsi, M. ulcerans, M. liflandi and M. kansasii.BLAST searches for the 321 bp sized sequence potentially coding for the esxA gene of M. acapulcensis resulted in 100% similarity with two short sequences of the type VII secretion system ESX-1 WXG100 family target ESAT-6 of MTBC species (M.tuberculosis).The two short sequences (31 and 29 base pairs respectively) overlapped with the primer annealing regions.Therefore the presence of an esxA gene orthologue in M. acapulcensis remains questionable.Phylogenetic profiling based on esxA and esxB sequences resulted in slow growing mycobacteria (SGM) roughly separating from rapid growing mycobacteria (RGM) as was shown for 16SrRNA sequences.SGM are mostly pathogenic mycobacterial species, while RGM are not known to be pathogenic or are sometimes known to cause opportunistic infections only.Phylogenetic trees based on esxA and esxB appeared more similar to each other than these trees were compared to the 16SrRNA-based phylogenetic tree.Discussion: Amplification of esxA and esxB gene sequences may be dependent on specific combinations of primers and NTM species, as different NTM were found to possess esxA and/or esxB orthologues than reported previously.Identification of esxB gene orthologues in M. engbackii and M. paraffinicum isolates confirms again that these genes do occur in non-pathogenic RGM species.In case of expression of ESAT-6 and CFP-10 by these mycobacterial species, infections with those NTM can cause false positive results in TB diagnostics when the antigens will be sufficient immunogenic.Therefore, the expression of ESAT-6 and CFP-10 should be further investigated and kept in mind when designing immunodiagnostic assays for TB.The phylogenetic classification of mycobacterial species based on esxA and esxB sequences can predict the potential pathogenicity of NTM species, but this classification does not predict NTM pathogenicity completely correct.This could be due to the fact that the proteins of the type VII secretion system are not the only virulence factors in mycobacterial species.EsxA-and esxB-based phylogenetic trees resembled each other more than the 16SrRNA-based phylogenetic tree, probably because sequences of different strains of the same mycobacterial species were used for the 16SrRNA-based tree.
Author: Agnes Bouw
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funder: Universiteit Utrecht
OpenAlex ID: W3041045865