Agnès Marot

Seasonal and regional dynamics of M. ulcerans transmission in environmental context: deciphering the role of water bugs as hosts and vectors.

Background Buruli ulcer, the third mycobacterial disease after tuberculosis and leprosy, is caused by the environmental mycobacterium M. ulcerans. Various modes of transmission have been suspected for this disease, with no general consensus acceptance for any of them up to now. Since laboratory models demonstrated the ability of water bugs to transmit M. ulcerans, a particular attention is focused on the transmission of the bacilli by water bugs as hosts and vectors. However, it is only through detailed knowledge of the biodiversity and ecology of water bugs that the importance of this mode of transmission can be fully assessed. It is the objective of the work here to decipher the role of water bugs in M. ulcerans ecology and transmission, based on large-scale field studies. Methodology/Principal Findings The distribution of M. ulcerans-hosting water bugs was monitored on previously unprecedented time and space scales: a total of 7,407 water bugs, belonging to large number of different families, were collected over one year, in Buruli ulcer endemic and non endemic areas in central Cameroon. This study demonstrated the presence of M. ulcerans in insect saliva. In addition, the field results provided a full picture of the ecology of transmission in terms of biodiversity and detailed specification of seasonal and regional dynamics, with large temporal heterogeneity in the insect tissue colonization rate and detection of M. ulcerans only in water bug tissues collected in Buruli ulcer endemic areas. Conclusion/Significance The large-scale detection of bacilli in saliva of biting water bugs gives enhanced weight to their role in M. ulcerans transmission. On practical grounds, beyond the ecological interest, the results concerning seasonal and regional dynamics can provide an efficient tool in the hands of sanitary authorities to monitor environmental risks associated with Buruli ulcer.

Protection against Mycobacterium ulcerans lesion development by exposure to aquatic insect saliva

Background Buruli ulcer is a severe human skin disease caused by Mycobacterium ulcerans. This disease is primarily diagnosed in West Africa with increasing incidence. Antimycobacterial drug therapy is relatively effective during the preulcerative stage of the disease, but surgical excision of lesions with skin grafting is often the ultimate treatment. The mode of transmission of this Mycobacterium species remains a matter of debate, and relevant interventions to prevent this disease lack (i) the proper understanding of the M. ulcerans life history traits in its natural aquatic ecosystem and (ii) immune signatures that could be correlates of protection. We previously set up a laboratory ecosystem with predatory aquatic insects of the family Naucoridae and laboratory mice and showed that (i) M. ulcerans-carrying aquatic insects can transmit the mycobacterium through bites and (ii) that their salivary glands are the only tissues hosting replicative M. ulcerans. Further investigation in natural settings revealed that 5%–10% of these aquatic insects captured in endemic areas have M. ulcerans–loaded salivary glands. In search of novel epidemiological features we noticed that individuals working close to aquatic environments inhabited by insect predators were less prone to developing Buruli ulcers than their relatives. Thus we set out to investigate whether those individuals might display any immune signatures of exposure to M. ulcerans-free insect predator bites, and whether those could correlate with protection. Methods and Findings We took a two-pronged approach in this study, first investigating whether the insect bites are protective in a mouse model, and subsequently looking for possibly protective immune signatures in humans. We found that, in contrast to control BALB/c mice, BALB/c mice exposed to Naucoris aquatic insect bites or sensitized to Naucoris salivary gland homogenates (SGHs) displayed no lesion at the site of inoculation of M. ulcerans coated with Naucoris SGH components. Then using human serum samples collected in a Buruli ulcer–endemic area (in the Republic of Benin, West Africa), we assayed sera collected from either ulcer-free individuals or patients with Buruli ulcers for the titre of IgGs that bind to insect predator SGH, focusing on those molecules otherwise shown to be retained by M. ulcerans colonies. IgG titres were lower in the Buruli ulcer patient group than in the ulcer-free group. Conclusions These data will help structure future investigations in Buruli ulcer–endemic areas, providing a rationale for research into human immune signatures of exposure to predatory aquatic insects, with special attention to those insect saliva molecules that bind to M. ulcerans.

A Multifaceted Study of Scedosporium boydii Cell Wall Changes during Germination and Identification of GPI-Anchored Proteins

Scedosporium boydii is a pathogenic filamentous fungus that causes a wide range of human infections, notably respiratory infections in patients with cystic fibrosis. The development of new therapeutic strategies targeting S. boydii necessitates a better understanding of the physiology of this fungus and the identification of new molecular targets. In this work, we studied the conidium-to-germ tube transition using a variety of techniques including scanning and transmission electron microscopy, atomic force microscopy, two-phase partitioning, microelectrophoresis and cationized ferritin labeling, chemical force spectroscopy, lectin labeling, and nanoLC-MS/MS for cell wall GPI-anchored protein analysis. We demonstrated that the cell wall undergoes structural changes with germination accompanied with a lower hydrophobicity, electrostatic charge and binding capacity to cationized ferritin. Changes during germination also included a higher accessibility of some cell wall polysaccharides to lectins and less CH3/CH3 interactions (hydrophobic adhesion forces mainly due to glycoproteins). We also extracted and identified 20 GPI-anchored proteins from the cell wall of S. boydii, among which one was detected only in the conidial wall extract and 12 only in the mycelial wall extract. The identified sequences belonged to protein families involved in virulence in other fungi like Gelp/Gasp, Crhp, Bglp/Bgtp families and a superoxide dismutase. These results highlighted the cell wall remodeling during germination in S. boydii with the identification of a substantial number of cell wall GPI-anchored conidial or hyphal specific proteins, which provides a basis to investigate the role of these molecules in the host-pathogen interaction and fungal virulence.

Identification of Scedosporium boydii catalase A1 gene, a reactive oxygen species detoxification factor highly expressed in response to oxidative stress and phagocytic cells.

Scedosporium boydii is an opportunistic filamentous fungus which may be responsible for a large variety of infections in both immunocompetent and immunocompromised individuals. This fungus belongs to the Scedosporium apiospermum species complex which usually ranks second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). Species of the S. apiospermum complex are able to chronically colonize the CF airways suggesting pathogenic mechanisms allowing persistence and growth of these fungi in the respiratory tract. Few putative virulence factors have been purified and characterized so far in the S. apiospermum complex including a cytosolic Cu,Zn-superoxide dismutase (SOD) and a monofunctional catalase (catalase A1). Upon microbial infection, host phagocytes release reactive oxygen species (ROS), such as hydrogen peroxide, as part of the antimicrobial response. Catalases are known to protect pathogens against ROS by degradation of the hydrogen peroxide. Here, we identified the S. boydii catalase A1 gene (CATA1) and investigated its expression in response to the environmental conditions encountered in the CF airways and to the oxidative stress. Results showed that S. boydii CATA1 gene expression is not affected by hypoxia, hypercapnia or pH changes. In contrast, CATA1 gene was overexpressed in response to a chemically induced oxidative stress with a relative gene expression 37-fold higher in the presence of 250 μM H(2)O(2), 20-fold higher with 250 μM menadione and 5-fold higher with 2 mM paraquat. Moreover, S. boydii CATA1 gene expression progressively increased upon exposure to activated THP-1-derived macrophages, reaching a maximum after 12 h (26 fold). Activated HL60-derived neutrophils and activated human peripheral blood neutrophils more rapidly induced S. boydii CATA1 gene overexpression, a maximum gene expression level being reached at 75 min (17 fold) and 60 min (15 fold), respectively. In contrast expression of the gene encoding the Cu,Zn-SOD (SODC gene) was not affected by H(2)O(2), menadione, paraquat or in co-culture with phagocytic cells. These results suggest that S. boydii CATA1 gene is highly stimulated by the oxidative burst response whereas SODC gene is constitutively expressed.

Diagnosis of dermatophytosis: an evaluation of direct examination using MycetColor® and MycetFluo®

Dermatophytes are an important cause of superficial fungal infection. Direct examination of skin, nail, or hair samples remains essential in diagnosis, as it provides a quick response to the clinician. However, mycological analysis, including direct examination and culture, often lacks sensitivity. The use of stains or fluorochromes may enhance the performance of direct examination. We analyzed 102 samples from patients with suspected dermatophytosis in 4 different diagnostic mycology laboratories. Two reagents, MycetColor® and MycetFluo®, which use Congo red and calcofluor dye, respectively, were evaluated for the direct microscopic examination of skin, hair, and nail specimens. The results were compared to those of culture and conventional direct examination. Both reagents were able to clarify the specimens and also to specifically stain fungal elements. Microscopic examination of the specimens was greatly facilitated with MycetFluo®, which allowed a higher number of positive cases to be detected compared to the other methods.

Diagnostic biologique des candidoses

Resume Les candidoses representent les infections fongiques les plus frequentes en pathologie humaine. Les techniques mycologiques classiques, de realisation simple, suffisent le plus souvent a poser un diagnostic de candidose superficielle. Dans un contexte de candidose profonde ou systemique, l’hemoculture represente toujours le « gold standard », meme si sa sensibilite peut etre prise en defaut. Au cours des dernieres decennies, un certain nombre de tests alternatifs a la culture ont ete developpes afin de pallier ce defaut de sensibilite. Ceux-ci reposent sur la detection d’anticorps, d’antigenes, de metabolites ou d’acides nucleiques. Les resultats de la serologie doivent, dans la grande majorite des cas, etre interpretes en fonction du statut immunitaire des patients et la recherche isolee d’anticorps specifiques est souvent peu contributive au diagnostic, si elle n’est pas associee a la recherche d’antigenes circulants. Ainsi, la recherche de mannanes circulants permet de detecter les infections causees par les principales especes de Candida ; la sensibilite de cette technique augmente avec la repetition des prelevements et la realisation conjointe de la detection d’anticorps anti-mannanes. De meme, la recherche de β(1,3)-D-glucanes, utilisee seule ou en association avec la recherche des mannanes, peut etre utile pour depister precocement une candidose profonde. La biologie moleculaire permet d’envisager le diagnostic de candidose profonde sans etre gene par le statut immunitaire du patient. Grâce a l’arrivee recente de kits commerciaux, la detection moleculaire des Candida devrait se democratiser dans les laboratoires. De meme, l’approche proteomique par MALDI-TOF permet de raccourcir considerablement les delais d’identification des especes isolees. Les methodes modernes de typage moleculaire, basees sur l’analyse de la variabilite du genome, ont remplace les techniques phenotypiques. Bien qu’insuffisamment standardisees, elles sont un outil precieux permettant de mieux apprehender l’epidemiologie des infections a Candida .

Scedosporium boydii CatA1 and SODC recombinant proteins, new tools for serodiagnosis of Scedosporium infection of patients with cystic fibrosis

Scedosporium species rank the second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF), after Aspergillus fumigatus. In CF, these fungi may cause various respiratory infections similar to those caused by A. fumigatus, including bronchitis and allergic broncho-pulmonary mycoses. Diagnosis of these infections relies on the detection of serum antibodies using crude antigenic extracts. However, many components of these extracts are common to Scedosporium and Aspergillus species, leading to cross-reactions. Here, 5 recombinant proteins from S. apiospermum or S. boydii were produced, and their value in serodiagnosis of Scedosporium infections was investigated by enzyme-linked immunosorbent assay. Two of them, corresponding to the Scedosporium catalase A1 or cytosolic Cu,Zn-superoxyde dismutase, allowed the detection of Scedosporium infection, and the differentiation with an Aspergillus infection. These recombinant proteins therefore may serve as a basis for the development of a standardized serological test.