Date Published: January 23, 2019
Publisher: Public Library of Science
Author(s): Natthanej Luplertlop, Watcharamat Muangkaew, Potjaman Pumeesat, San Suwanmanee, Pantira Singkum, Wolfgang Arthofer.
Scedosporium is a genus comprising at least 10 species of airborne fungi (saprobes) that survive and grow on decaying organic matter. These fungi are found in high density in human-affected areas such as sewage-contaminated water, and five species, namely Scedosporium apiospermum, S. boydii, S. aurantiacum, S. dehoogii, and S. minutisporum, cause human infections. Thailand is a popular travel destination in the world, with many attractions present in densely populated areas; thus, large numbers of people may be exposed to pathogens present in these areas. We conducted a comprehensive survey of Scedosporium species in 350 soil samples obtained from 35 sites of high human population density and tourist popularity distributed over 23 provinces and six geographic regions of Thailand. Soil suspensions of each sample were inoculated on three plates of Scedo-Select III medium to isolate Scedosporium species. In total, 191 Scedosporium colonies were isolated from four provinces. The species were then identified using PCR and sequencing of the beta-tubulin (BT2) gene. Of the 191 isolates, 188 were S. apiospermum, one was S. dehoogii, and species of two could not be exactly identified. Genetic diversity analysis revealed high haplotype diversity of S. apiospermum. Soil is a major ecological niche for Scedosporium and may contain S. apiospermum populations with high genetic diversity. This study of Scedosporium distribution might encourage health care providers to consider Scedosporium infection in their patients.
Scedosporium is a genus of filamentous fungi with septate hyphae. These fungi are airborne saprobes that survive and grow on decaying organic matter, and thus, are frequently found in high density in human-affected areas such as sewage, contaminated water, and urban soil. The genus currently comprises 10 species, five of which, namely Scedosporium apiospermum, S. boydii, S. aurantiacum, S. dehoogii, and S. minutisporum, cause Scedosporiosis. . This disease has recently emerged as a severe fungal infection from environmental sources. Scedosporium biology has been studied mainly after its isolation from the environment. In Thailand, S. apiospermum was reported in brain abscesses of near-drowning individuals . Moreover, two Swiss tourists who nearly drowned in a tsunami disaster were infected with S. apiospermum .
In this study, 350 soil samples were collected from 35 public parks that were distributed across 23 provinces of Thailand (Table 1). In total, 191 morphologically distinct colonies of Scedosporium were selected for species and strain identification based on Bt2 gene sequencing. Of the 191 isolates, 188 were S. apiospermum (76 isolates from Pumrak Park, 44 isolates from Asdang Park, and 32 isolates from Nongkae Chang Park in Nakhon Ratchasima Province; 33 isolates from Bueng Phraram Public Park in Phra Nakhon Si Ayutthaya Province; one isolate from Chaloem Phrakiat Health Park in Samut Songkhram Province; and two isolates from Municipal Public Park in Prachuap Khiri Khan Province), and one isolate of S. dehoogii (TMMI154; isolated from Pumrak Park in Nakhon Ratchasima Province) as summarized in Fig 1. In addition, the species of two isolates (TMMI275 from Nongkae Chang Park in Nakhon Ratchasima Province and TMMI293 from Bueng Phraram Public Park in Phra Nakhon Si Ayutthaya Province) could not be identified.
There are several molecular techniques applied to identify Scedosporium species. Sequencing techniques, including Multi-Locus Sequence Typing (MLST), is widely used for identification of these fungi. The target gene using for sequencing are internal transcribed spacer (ITS), actin, calmodulin exons 3 and 4, the second largest subunit of the RNA polymerase II and Beta-tubulin exon 2–4, manganese superoxide dismutase, transcription elongation 1 alpha, Beta -tubulin exon 5–6 . Researchers have also used the internal transcribe spacer-restriction fragment length polymorphism (ITS-RFLP) technique, M13 PCR fingerprint, quantitative Real-Time PCR (qPCR), PCR-based reverse line blotting (PCR-RLB) and loop-mediated isothermal amplification (LAMP) [16–17]. Isolates should be characterized phenotypically as well as with molecular techniques to confirm Scedosporium species identification.
In conclusion, this study identified soil as an ecological niche of Scedosporium in Thailand. The results provide valuable knowledge to assist future studies to compare genetic relatedness among pathogenic species in the clinical setting and to evaluate infection risk in specific regions.