Abstract
BackgroundHighly pathogenic mycobacteria like Mycobacterium tuberculosis are characterised by their slow growth and their ability to reside and multiply in the very hostile phagosomal environment and a correlation between the growth rate of mycobacteria and their pathogenicity has been hypothesised. Here, porin genes from M. fortuitum were cloned and characterised to address their impact on the growth rate of fast-growing and pathogenic mycobacteria.ResultsTwo genes encoding porins orthologous to MspA from M. smegmatis, porM1 and porM2, were cloned from M. fortuitum strains, which were originally isolated from human patients. Both porin genes were at least partially able to complement the mutations of a M. smegmatis mutant strain lacking the genes mspA and mspC with respect to the growth rate. PorM1 and porM2 were present in different strains of M. fortuitum including the type strain. Comparative expression analysis of porM genes revealed divergent porin expression among analysed M. fortuitum strains. Repression of the expression of porins by antisense technique decreased the growth rates of different M. fortuitum. The effects of over-expression of porM1 as well as porM2 varied depending on the strain and the concentration of antibiotic added to the medium and indicated that PorM1 and PorM2 enhance the growth of M. fortuitum strains, but also the diffusion of the antibiotic kanamycin into the cells.ConclusionThis study demonstrates the important role of porin expression in growth as well as antibiotic susceptibility of the opportunistic bacterium M. fortuitum.
Highlights
Pathogenic mycobacteria like Mycobacterium tuberculosis are characterised by their slow growth and their ability to reside and multiply in the very hostile phagosomal environment and a correlation between the growth rate of mycobacteria and their pathogenicity has been hypothesised
This study demonstrates the important role of porin expression in growth as well as antibiotic susceptibility of the opportunistic bacterium M. fortuitum
The M. fortuitum group is involved in 60% of localised cutaneous infections in immunocompetent persons caused by rapidly growing mycobacteria (RGM) but is a rare cause of pulmonary disease
Summary
Pathogenic mycobacteria like Mycobacterium tuberculosis are characterised by their slow growth and their ability to reside and multiply in the very hostile phagosomal environment and a correlation between the growth rate of mycobacteria and their pathogenicity has been hypothesised. The species of RGM able to cause human disease basically belong to the M. fortuitum group, the M. chelonae/abscessus group and the M. smegmatis group. Members of these groups are commonly seen in aquatic environments like municipal tap water, and health care-. Most or all of the cases of community-acquired or health care-associated diseases caused by the M. fortuitum group are due to M. fortuitum. This species basically causes skin lesions, wound infections, postinjection abscesses, postsurgical wound infections or pulmonary disease in previously healthy hosts [1]. Cirillo et al [2] and Da Silva et al [3] reported that M. fortuitum was capable to replicate in amoebae and murine monocytic cells, respectively
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