Mycobacterium llatzerense, a waterborne Mycobacterium, that resists phagocytosis by Acanthamoeba castellanii

Vincent Delafont,Yann Héchard,Emmanuelle Cambau,Ascel Samba-Louaka,Laurent Moulin,Didier Bouchon

doi:10.1038/srep46270

Abstract

Nontuberculous mycobacteria (NTM) are environmental bacteria increasingly associated to public health problems. In water systems, free-living amoebae (FLA) feed on bacteria by phagocytosis, but several bacteria, including many NTM, are resistant to this predation. Thus, FLA can be seen as a training ground for pathogenic bacteria. Mycobacterium llatzerense was previously described as frequently associated with FLA in a drinking water network. The present study aimed to characterize the interactions between M. llatzerense and FLA. M. llatzerense was internalised by phagocytosis and featured lipid inclusions, suggesting a subversion of host resources. Moreover, M. llatzerense survived and even multiplied in presence of A. castellanii. Using a genomic-based comparative approach, twelve genes involved in phagocytosis interference, described in M. tuberculosis, were identified in the M. llatzerense genome sequenced in this study. Transcriptomic analyses showed that ten genes were significantly upregulated during the first hours of the infection, which could partly explain M. llatzerense resistance. Additionally, M. llatzerense was shown to actively inhibit phagosome acidification. In conclusion, M. llatzerense presents a high degree of resistance to phagocytosis, likely explaining its frequent occurrence within FLA in drinking water networks. It underscores that NTM should be carefully monitored in water networks to prevent human health concerns.

Highlights

Nontuberculous mycobacteria (NTM) are environmental bacteria increasingly associated to public health problems
Using a genomic-based comparative approach, twelve genes involved in phagocytosis interference, described in M. tuberculosis, were identified in the M. llatzerense genome sequenced in this study
We recently reported the frequent occurrence of free-living amoebae (FLA)-NTM association in the drinking water network of Paris, France, and identified M. llatzerense as a predominant NTM co-occurring with FLA33

Summary

Introduction

Nontuberculous mycobacteria (NTM) are environmental bacteria increasingly associated to public health problems. M. llatzerense presents a high degree of resistance to phagocytosis, likely explaining its frequent occurrence within FLA in drinking water networks It underscores that NTM should be carefully monitored in water networks to prevent human health concerns. Resistance of environmental NTM to FLA was investigated using Mycobacterium avium, the major slowly-growing species involved in NTM diseases[28] During infection of both human macrophages and FLA, it was demonstrated that a species-specific pathogenicity island was involved in the successful invasion of host cells by M. avium[29]. Another NTM studied is Mycobacterium abscessus, the major rapidly growing mycobacteria involved in human diseases[30,31]. The involvement of M. llatzerense was recently reported in immunocompromised patients, raising the possibility that it may be an opportunistic pathogen as well[39,40,41]

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