Soutenance de thèse de NASSIM HAMMOUDI

Mycobacterium ulcerans is a non-tuberculous mycobacterium, causes Buruli Ulcer which is a neglected tropical disease reported in 36 countries. M. ulcerans belongs to the group of mycolactone-producing mycobacteria (MPMs), closely related to Mycobacterium marinum (M. marinum). M. ulcerans is secreting mycolactone toxins which are the main virulence factor, responsible for skin ulcers and underlying tissue and bone, leading to permanent deformities and disability. The reservoir and the mode of contamination of M. ulcerans are not formally known, limiting the initiation of prophylaxis in endemic countries. Based on the "One Health" approach, my thesis aims to contribute unmasking the reservoir(s) and mode(s) of contamination of M. ulcerans. My review of the literature dedicated to the study of the genomic diversity of the MPMs complex and the M. marinum group, highlights the taxonomy of these mycobacteria in order to understand the epidemiology of Buruli Ulcer. My study of methods for decontamination and culture of M. ulcerans has led to the development of a decontamination medium for environmental samples and a culture medium for M. ulcerans; which I used to culture several species of mycobacteria in the rhizosphere of plants in which M. ulcerans DNA was detected by PCR. Then, I determined a list of plants associated with M. ulcerans which may be sources of contamination of the population in Côte d'Ivoire. The mode of transmission of M. ulcerans to humans is still unclear. Experimental models have shown that different types of lesions, including mosquito bites on contaminated skin, can cause Buruli ulcer. Investigating the sources of contamination of populations in endemic areas, we traced a new chain of transmission of M. ulcerans from the bushmeat (aulacodes) that can be infected by eating plant roots contaminated with M. ulcerans. On the other hand, I have shown the spread of M. ulcerans in the spleens of these animals. An animal model of M. ulcerans ingestion that I performed in our laboratory confirmed the translocation of M. ulcerans from the gut to different organs of the rat. In addition, my study on skin ulcer in Burkina Faso showed for the first time since the 90s the involvement of M. ulcerans in skin ulcers in this country. I further showed an asymptomatic carriage of M. ulcerans on the healthy skin of farmers in Burkina Faso, and the significant presence of Aspergillus sp. in the skin microbiota of these individuals. The presence of this fungus is not fortuitous because I subsequently observed an attraction phoneme of Aspergillus. sp. by the mycolactone secreted by M. ulcerans. Focusing on this observation, I extended my study to three other fungi species, namely Mucor circinelloides, Scedosporium apiospermum and Fusarium equiseti, showing the attracting effect of mycolactone on the fungus M. circinelloides. These observations unmask a new activity of mycolactone which consists in attracting mobile unicellular organisms such as microscopic fungi, which could be the primary function of mycolactone in the ecological niches where M. ulcerans lives and multiplies. Keywords: Mycobacterium ulcerans, Buruli ulcer, infection, environment, Animals, plants.

Mycobacterium ulcerans is a non-tuberculous mycobacterium, causes Buruli Ulcer which is a neglected tropical disease reported in 36 countries. M. ulcerans belongs to the group of mycolactone-producing mycobacteria (MPMs), closely related to Mycobacterium marinum (M. marinum). M. ulcerans is secreting mycolactone toxins which are the main virulence factor, responsible for skin ulcers and underlying tissue and bone, leading to permanent deformities and disability. The reservoir and the mode of contamination of M. ulcerans are not formally known, limiting the initiation of prophylaxis in endemic countries. Based on the "One Health" approach, my thesis aims to contribute unmasking the reservoir(s) and mode(s) of contamination of M. ulcerans. My review of the literature dedicated to the study of the genomic diversity of the MPMs complex and the M. marinum group, highlights the taxonomy of these mycobacteria in order to understand the epidemiology of Buruli Ulcer. My study of methods for decontamination and culture of M. ulcerans has led to the development of a decontamination medium for environmental samples and a culture medium for M. ulcerans; which I used to culture several species of mycobacteria in the rhizosphere of plants in which M. ulcerans DNA was detected by PCR. Then, I determined a list of plants associated with M. ulcerans which may be sources of contamination of the population in Côte d'Ivoire. The mode of transmission of M. ulcerans to humans is still unclear. Experimental models have shown that different types of lesions, including mosquito bites on contaminated skin, can cause Buruli ulcer. Investigating the sources of contamination of populations in endemic areas, we traced a new chain of transmission of M. ulcerans from the bushmeat (aulacodes) that can be infected by eating plant roots contaminated with M. ulcerans. On the other hand, I have shown the spread of M. ulcerans in the spleens of these animals. An animal model of M. ulcerans ingestion that I performed in our laboratory confirmed the translocation of M. ulcerans from the gut to different organs of the rat. In addition, my study on skin ulcer in Burkina Faso showed for the first time since the 90s the involvement of M. ulcerans in skin ulcers in this country. I further showed an asymptomatic carriage of M. ulcerans on the healthy skin of farmers in Burkina Faso, and the significant presence of Aspergillus sp. in the skin microbiota of these individuals. The presence of this fungus is not fortuitous because I subsequently observed an attraction phoneme of Aspergillus. sp. by the mycolactone secreted by M. ulcerans. Focusing on this observation, I extended my study to three other fungi species, namely Mucor circinelloides, Scedosporium apiospermum and Fusarium equiseti, showing the attracting effect of mycolactone on the fungus M. circinelloides. These observations unmask a new activity of mycolactone which consists in attracting mobile unicellular organisms such as microscopic fungi, which could be the primary function of mycolactone in the ecological niches where M. ulcerans lives and multiplies. Keywords: Mycobacterium ulcerans, Buruli ulcer, infection, environment, Animals, plants.