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Germ tube mediated invasion of Batrachochytrium dendrobatidis in amphibian skin is host dependent.

Van Rooij P, Martel A, D'Herde K, Brutyn M, Croubels S, Ducatelle R, Haesebrouck F, Pasmans F - PLoS ONE (2012)

Bottom Line: Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm.Only the superficial epidermis was affected.These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. pascale.vanrooij@ugent.be

ABSTRACT
Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, a fungal skin disease in amphibians and driver of worldwide amphibian declines.We focussed on the early stages of infection by Bd in 3 amphibian species with a differential susceptibility to chytridiomycosis. Skin explants of Alytes muletensis, Litoria caerulea and Xenopus leavis were exposed to Bd in an Ussing chamber for 3 to 5 days. Early interactions of Bd with amphibian skin were observed using light microscopy and transmission electron microscopy. To validate the observations in vitro, comparison was made with skin from experimentally infected frogs. Additional in vitro experiments were performed to elucidate the process of intracellular colonization in L. caerulea. Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm. Inoculation of A. muletensis and L. caerulea skin was followed within 24 h by endobiotic development, with sporangia located intracellularly in the skin. Evidence is provided of how intracellular colonization is established and how colonization by Bd proceeds to deeper skin layers. Older thalli develop rhizoid-like structures that spread to deeper skin layers, form a swelling inside the host cell to finally give rise to a new thallus. In X. laevis, interaction of Bd with skin was limited to an epibiotic state, with sporangia developing upon the skin. Only the superficial epidermis was affected. Epidermal cells seemed to be used as a nutrient source without development of intracellular thalli. The in vitro data agreed with the results obtained after experimental infection of the studied frog species. These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

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Light microscopical overview of the development of Bd in skin explants of Alytes muletensis and Litoria caerulea.(A) at 1 day post infection (dpi) germlings have developed germ tubes (arrow) that invade the epidermis of A. muletensis; Gomori methenamine silver (GMS) stain; scale bar = 10 µm; (B) at 1 dpi both Bd germlings (black arrow) attached upon the epidermal surface as intracellular chytrid thalli (white arrow) in the stratum corneum of L. caerulea are observed; haematoxylin and eosin stain; scale bar = 10 µm.
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pone-0041481-g003: Light microscopical overview of the development of Bd in skin explants of Alytes muletensis and Litoria caerulea.(A) at 1 day post infection (dpi) germlings have developed germ tubes (arrow) that invade the epidermis of A. muletensis; Gomori methenamine silver (GMS) stain; scale bar = 10 µm; (B) at 1 dpi both Bd germlings (black arrow) attached upon the epidermal surface as intracellular chytrid thalli (white arrow) in the stratum corneum of L. caerulea are observed; haematoxylin and eosin stain; scale bar = 10 µm.

Mentions: Figure 3 illustrates the development of Bd in skin explants of A. muletensis and L. caerulea. Compared to X. laevis, a similar initial infection process was seen in A. muletensis and L caerulea. Likewise, zoospore cysts adhered to the stratum corneum, host cells were invaded by germ tubes that developed into rhizoidal axes spreading out in the entire cell (Figs. 3A,B). Invasion of the keratinocytes by germ tubes and loss of the cellular cytoplasm was most obvious by TEM (Figs. 4A,B). From 2 dpi on, maturing sporangia were observed upon the infected skin surface. However, the development of Bd in A. muletensis and L. caerulea was clearly distinct in the respect that besides superficial colonization, intracellular chytrid thalli were observed in superficial and deeper layers of the epidermis. Within 24 hours after inoculation, marked intracellular colonization was seen in L. caerulea by LM (Fig. 3B) and TEM (Fig. 4B) and occasional intracellular colonization in A. muletensis.


Germ tube mediated invasion of Batrachochytrium dendrobatidis in amphibian skin is host dependent.

Van Rooij P, Martel A, D'Herde K, Brutyn M, Croubels S, Ducatelle R, Haesebrouck F, Pasmans F - PLoS ONE (2012)

Light microscopical overview of the development of Bd in skin explants of Alytes muletensis and Litoria caerulea.(A) at 1 day post infection (dpi) germlings have developed germ tubes (arrow) that invade the epidermis of A. muletensis; Gomori methenamine silver (GMS) stain; scale bar = 10 µm; (B) at 1 dpi both Bd germlings (black arrow) attached upon the epidermal surface as intracellular chytrid thalli (white arrow) in the stratum corneum of L. caerulea are observed; haematoxylin and eosin stain; scale bar = 10 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3401113&req=5

pone-0041481-g003: Light microscopical overview of the development of Bd in skin explants of Alytes muletensis and Litoria caerulea.(A) at 1 day post infection (dpi) germlings have developed germ tubes (arrow) that invade the epidermis of A. muletensis; Gomori methenamine silver (GMS) stain; scale bar = 10 µm; (B) at 1 dpi both Bd germlings (black arrow) attached upon the epidermal surface as intracellular chytrid thalli (white arrow) in the stratum corneum of L. caerulea are observed; haematoxylin and eosin stain; scale bar = 10 µm.
Mentions: Figure 3 illustrates the development of Bd in skin explants of A. muletensis and L. caerulea. Compared to X. laevis, a similar initial infection process was seen in A. muletensis and L caerulea. Likewise, zoospore cysts adhered to the stratum corneum, host cells were invaded by germ tubes that developed into rhizoidal axes spreading out in the entire cell (Figs. 3A,B). Invasion of the keratinocytes by germ tubes and loss of the cellular cytoplasm was most obvious by TEM (Figs. 4A,B). From 2 dpi on, maturing sporangia were observed upon the infected skin surface. However, the development of Bd in A. muletensis and L. caerulea was clearly distinct in the respect that besides superficial colonization, intracellular chytrid thalli were observed in superficial and deeper layers of the epidermis. Within 24 hours after inoculation, marked intracellular colonization was seen in L. caerulea by LM (Fig. 3B) and TEM (Fig. 4B) and occasional intracellular colonization in A. muletensis.

Bottom Line: Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm.Only the superficial epidermis was affected.These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. pascale.vanrooij@ugent.be

ABSTRACT
Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, a fungal skin disease in amphibians and driver of worldwide amphibian declines.We focussed on the early stages of infection by Bd in 3 amphibian species with a differential susceptibility to chytridiomycosis. Skin explants of Alytes muletensis, Litoria caerulea and Xenopus leavis were exposed to Bd in an Ussing chamber for 3 to 5 days. Early interactions of Bd with amphibian skin were observed using light microscopy and transmission electron microscopy. To validate the observations in vitro, comparison was made with skin from experimentally infected frogs. Additional in vitro experiments were performed to elucidate the process of intracellular colonization in L. caerulea. Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm. Inoculation of A. muletensis and L. caerulea skin was followed within 24 h by endobiotic development, with sporangia located intracellularly in the skin. Evidence is provided of how intracellular colonization is established and how colonization by Bd proceeds to deeper skin layers. Older thalli develop rhizoid-like structures that spread to deeper skin layers, form a swelling inside the host cell to finally give rise to a new thallus. In X. laevis, interaction of Bd with skin was limited to an epibiotic state, with sporangia developing upon the skin. Only the superficial epidermis was affected. Epidermal cells seemed to be used as a nutrient source without development of intracellular thalli. The in vitro data agreed with the results obtained after experimental infection of the studied frog species. These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.

Show MeSH
Related in: MedlinePlus