Bouam, A. | bioRxiv Science

bioRxiv2020

Translocating Mycobacterium ulcerans: an experimental model.

Mycobacterium ulcerans is a non-tuberculous environmental mycobacterium responsible for extensive cutaneous and subcutaneous ulcers in mammals, named Buruli ulcer in patients. M. ulcerans has been seldom detected in the feces of mammals but not in patients, nevertheless the detection and isolation of M. ulcerans in animal feces does not feet with the current epidemiological schemes for the disease. Here using an experimental model in which rats were fed with 109 colony-forming units of M. ulcerans, we detected M. ulcerans in feces of challenged rats for two weeks and along their digestive tract for 10 days. M. ulcerans was further detected in the lymphatic system including cervical and axillary lymph nodes and the spleen, but not in any other tissue including the healthy and breached skin, 10 days post-challenge. These observations indicate that in some herbivorous mammals, M. ulcerans contamination by the digestive route may precede translocation and limited infection of the lymphatic tissues without systemic infection. These herbivorous mammals may be sources of M. ulcerans for exposed populations but are unlikely reservoirs for the pathogen.

microbiology↗

bioRxiv2019

Investigation of skin microbiota reveals Mycobacterium ulcerans-Aspergillus sp. trans-kingdom communication

BackgroundMycobacterium ulcerans secrete a series of non-ribosomal-encoded toxins known as mycolactones that are responsible for causing a disabling ulceration of the skin and subcutaneous tissues named Buruli ulcer. The disease is the sole non-contagion among the three most common mycobacterial diseases in humans. Direct contact with contaminated wetlands is a risk factor for Buruli ulcer, responsible for M. ulcerans skin carriage before transcutaneous inoculation with this opportunistic pathogen. Methodology and principal findingsIn this study, we analysed the bacterial and fungal skin microbiota in individuals exposed to M. ulcerans in Burkina Faso. We showed that M. ulcerans-specific DNA sequences were detected on the unbreached skin of 6/52 (11.5%) asymptomatic farmers living in Sindou versus 0/52 (0%) of those living in the non-endemic region of Tenkodogo. Then, we cultured the skin microbiota of asymptomatic M. ulcerans carriers and negative control individuals, all living in the region of Sindou. A total of 84 different bacterial and fungal species were isolated, 21 from M. ulcerans-negative skin samples, 31 from M. ulcerans-positive samples and 32 from both. More specifically, Actinobacteria, Aspergillus niger and Aspergillus flavus were significantly associated with M. ulcerans skin carriage. We further observed that in vitro, mycolactones induced spore germination of A. flavus, attracting the fungal network. ConclusionThese unprecedented observations suggest that interactions with fungi may modulate the outcome of M. ulcerans skin carriage, opening new venues to the understanding of Buruli ulcer pathology, prophylaxis and treatment of this still neglected tropical infection. Author summaryBuruli ulcer is a chronic infectious disease caused by the environmental opportunistic pathogen Mycobacterium ulcerans which secretes an exotoxin responsible for its pathogenicity. The reservoir and sources of M. ulcerans in the environment remain elusive and its mode of transmission is unclear. To acquire M. ulcerans infection, at least two conditions must be met, viable bacteria and a skin lesion as demonstrated by experimental animal models. In this study, we showed that M. ulcerans specific DNA sequences could be detected on the healthy skin of asymptomatic farmers living in one region of Burkina Faso where Buruli ulcer cases had already been reported, but not in Buruli ulcer-free regions, suggesting skin carriage after contacts with environmental sources. We also investigated the skin microbiota of M. ulcerans carriers and found significant associations of some bacteria and fungi with skin carriage of M. ulcerans. These associations may due to the effect of mycolactones on some fungi species. As we showed previously with Mucor circinelloides and here with Aspergillus flavus.

microbiology↗

bioRxiv2019

Mycolactone-independent pathogenicity of Mycobacterium ulcerans: an experimental study in plants.

Mycobacterium ulcerans, the etiologic agent of Buruli ulcer in humans and animals, secretes macrolide exotoxins mycolactones which damage tissues after a cascade of cellular effects. M. ulcerans, an environmental organism with still elusive reservoirs and sources has been detected in soil and water in endemic areas where it could be in contact with plants. Symptom observations, microscopy and molecular biology were used to investigate M. ulcerans contact with plants in an experimental model mimicking the known pathology of Buruli ulcer in humans. Solanum lycopereum (tomato) plants with scarified or intact roots were transplanted into pots containing contaminated soil with M. ulcerans or a mixture of mycolactones A/B and C in the presence of negative control groups. Whereas plants with intact roots remained asymptomatic, M. ulcerans-infected plants with scarified roots had significantly more diseased leaves than controls (p = 0.004). Optic microscopy examination showed significantly more mycobacteria in the secondary and main roots than in controls (p=0.0008). Real-time PCRs detected M. ulcerans DNA in 7/12 (58%) of infected root samples versus none in the control plants (p = 0.04). Further study of plants with mycolactones A/B and C yielded no significant difference with negative controls. These results suggest that in this model, M. ulcerans exhibits a mycolactone-independent pathogenicity whose mechanism remains to be elucidated.

microbiology↗