MgtC as a Host-Induced Factor and Vaccine Candidate against Mycobacterium abscessus Infection

Abstract

g Mycobacterium abscessus is an emerging pathogenic mycobacterium involved in pulmonary and mucocutaneous infections, presenting a serious threat for patients with cystic fibrosis (CF). The lack of an efficient treatment regimen and the emergence of multidrug resistance in clinical isolates require the development of new therapeutic strategies against this pathogen. Reverse genetics has revealed genes that are present in M. abscessus but absent from saprophytic mycobacteria and that are potentially involved in pathogenicity. Among them, MAB_3593 encodes MgtC, a known virulence factor involved in intramacrophage survival and adaptation to Mg 2؉ deprivation in several major bacterial pathogens. Here, we demonstrated a strong induction of M. abscessus MgtC at both the transcriptional and translational levels when bacteria reside inside macrophages or upon Mg 2؉ deprivation. Moreover, we showed that M. abscessus MgtC was recognized by sera from M. abscessus-infected CF patients. The intramacrophage growth (J774 or THP1 cells) of a M. abscessus knockout mgtC mutant was, however, not significantly impeded. Importantly, our results indicated that inhibition of MgtC in vivo through immunization with M. abscessus mgtC DNA, formulated with a tetrafunctional amphiphilic block copolymer, exerted a protective effect against an aerosolized M. abscessus challenge in CF (⌬F508 FVB) mice. The formulated DNA immunization was likely associated with the production of specific MgtC antibodies, which may stimulate a protective effect by counteracting MgtC activity during M. abscessus infection. These results emphasize the importance of M. abscessus MgtC in vivo and provide a basis for the development of novel therapeutic tools against pulmonary M. abscessus infections in CF patients. Mycobacterium abscessus, a rapidly growing mycobacterium (RGM), is the etiological agent of a wide spectrum of infections in humans. M. abscessus is responsible for severe and persistent pulmonary infections, disseminated cutaneous diseases, and posttrauma and postsurgery wound infections, mostly in immunocompetent patients and in cystic fibrosis (CF) patients (1-5). Infections by this pathogen lead to a fatality rate that is higher than those seen with other RGM species. Infection of CF patients with M. abscessus is a major health-related issue in most CF centers worldwide (1, 2, 6, 7) and is considered a contraindication to lung transplantation, leaving these patients with minimal therapeutic options.M. abscessus provokes very challenging therapeutic issues because of its natural resistance to most available antibiotics (8-10) and is considered the most drug-resistant mycobacterial species. The lack of optimal therapeutic treatments and the emergence of multidrug resistance in M. abscessus stress the need for the discovery of new strategies to combat these infections.Reverse genetics, based on the comparison between pathogenic and nonpathogenic species, allows the identification of genes missing in nonpathogenic species and encoding potential virulence...

The Diverse Cellular and Animal Models to Decipher the Physiopathological Traits of Mycobacterium abscessus Infection

“…These studies emphasize the usefulness of amoebae as a host model to identify and study determinants important in sustaining Mabs virulence (Halloum et al, 2016). Despite the failure of isolating Mabs from environmental sources, studies with Acanthamoeba suggest that Mabs has evolved in close contact with environmental protozoa and support the view that amoebae contribute in shaping Mabs virulence (Bakala N'Goma et al, 2015; Le Moigne et al, 2016). …”

“…This has recently stimulated studies aimed at describing interactions between Mabs and Ancathamoeba castellanii , an amoeba used as a model species to study the interaction with many different microorganisms (Guimaraes et al, 2016). Co-cultures have shown the induced expression of several Mabs virulence determinants, such as the phospholipase C or MgtC when Mabs is present inside the amoeba (Bakala N'Goma et al, 2015; Le Moigne et al, 2016). Additionally, a Mabs R mutant defective in cording showed severely impaired replication in both macrophages and amoebae, presumably due to limited inhibition of the phagolysosomal fusion.…”

Identification of genes required for Mycobacterium abscessus growth in vivo with a prominent role of the ESX-4 locus

“…Interestingly, these bacteria can also be found in amoebae (30,31) and share with M. abscessus the same pathophysiological niche, such as the CF patient airways. Of interest, phospholipase C and the magnesium transporter MgtC, which are often associated with the intracellular survival capacity of diverse pathogens, have been found to be induced in M. abscessus grown inside or in contact with amoebae or macrophages (MΦ) (10,32). These observations suggest that M. abscessus strains are equipped with a genetic arsenal acquired during their evolution to survive within environmental amoebae.…”

“…S2A, ΔeccB 4 was obtained by allelic exchange of nearly the entire eccB 4 coding sequence with a zeocin-resistance cassette (SI Appendix, Fig. S2B) (10,32). The complemented strain (C.ΔeccB 4 ) was obtained by cloning the eccB 4 gene under control of the hsp60 promoter in the integrative plasmid pMVH361, introducing this construct into ΔeccB 4 , and selecting recombinant clones with zeocin and hygromycin.…”

MmpL8 MAB controls Mycobacterium abscessus virulence and production of a previously unknown glycolipid family

“…A KO was performed in the M. abscessus subsp. abscessus S and R ATCC19977 strains using the recombineering approach (36,39,42,73,74). Complementation was performed by electrotransforming the mutant strains with the integrative vectors pMVH361::mmpL8 MAB and pMVH361::MYCMA_0439.…”