Molecular Phylogeny of the Pseudallescheria boydii Species Complex: Proposal of Two New Species

Abstract

Pseudallescheria boydii (anamorph Scedosporium apiospermum) is the species responsible for human scedosporiosis, a fungal infection with a high mortality rate and which is difficult to treat. Recently, it has been demonstrated that high genetic variation exists within this species. We have performed a morphological and molecular study involving numerous strains of clinical or environmental origins and from different countries. The analysis of partial sequences of the ␤-tubulin (two loci) and calmodulin genes and the internal transcribed spacer region of the rRNA gene has demonstrated that P. boydii is a species complex. The combined analysis of the sequences of the four loci of 60 strains has showed the presence of 44 haplotypes in the ingroup. Three species morphologically related to P. boydii sensu stricto, i.e., Pseudallescheria angusta, Pseudallescheria ellipsoidea, and Pseudallescheria fusoidea, which had previously been considered synonyms, could be differentiated genetically from P. boydii in our study. It is relevant that two of the three strains now included in P. ellipsoidea have caused invasive infections. The species Pseudallescheria minutispora and Scedosporium aurantiacum are clearly phylogenetically separated from the other species studied and are here proposed as new. Morphological features support this proposal. All the strains included in S. aurantiacum species have a clinical origin, while those included in P. minutispora are environmental. Further studies are needed to demonstrate whether all the species included in the P. boydii complex have different clinical spectra and antifungal susceptibility.Pseudallescheria boydii (anamorph Scedosporium apiospermum) is a ubiquitous ascomycetous fungus that causes a wide array of human infections that can affect practically all the organs of the body (8). These infections have been known for a long time, but in recent years, a marked increase in severe invasive infections has been noticed, mainly in immunocompromised hosts. The treatment of these infections has not yet been resolved, and the mortality rate is very high (3, 17). One of the most typical features of this species, which is very rare in other pathogenic fungi, is its ability to develop sexual structures on routine culture media. The presence of spherical ascomata (cleistothecia) and fusiform or ellipsoidal ascospores allows easy identification of this species and its differentiation from the other species of Scedosporium, Scedosporium prolificans, whose sexual state still remains unknown.On the basis of nuclear DNA-DNA reassociation, some studies have proved that important genetic variation exists in P. boydii. Gueho and de Hoog (10) found three infraspecific ecological and clinical groups. Rainer et al. (16) reported the existence of five different small-subunit rRNA gene sequence lengths. Random amplified polymorphic DNA studies also demonstrated that numerous and very different genotypes can be found (7). Other authors have reported considerable differences with respect to growth and sp...

Molecular Typing of AustralianScedosporiumIsolates Showing Genetic Variability and NumerousS. aurantiacum

“…In line with previously reported genetic variability in the S. apiospermum/P. boydii species complex (30-32), we observed 2 distinct ITS-RFLP patterns among S. apiospermum isolates, showing the presence of the newly described species S. aurantiacum (11). Notably, we have identifi ed by ITS sequencing that S. aurantiacum comprised 45% of the current collection of Australian "S. apiospermum" isolates and documents genetic variability within S. aurantiacum.…”

“…Given that S. aurantiacum is phylogenetically more closely related to S. apiospermum than to S. prolifi cans (11,33; current study), this result was unexpected. It may be due to different evolutionary pressures acting on the 3 different species or the relatively small numbers of S. aurantiacum isolates studied to date.…”

“…This species also colonizes the respiratory tract of ≈10% of patients with cystic fi brosis and chronic suppurative lung disease (8)(9)(10). On the basis of genetic data, a new species, S. aurantiacum, was proposed for a subset of isolates previously identifi ed as S. apiospermum (11). S. prolifi cans infections are geographically more restricted than those caused by S. apiospermum, being most prevalent in Australia, Spain, and the United States (12)(13)(14)(15).…”

Multilocus differentiation of the related dermatophytes Microsporum canis, Microsporum ferrugineum and Microsporum audouinii

“…recent studies have shown that b-tubulin is a good target for identification of opportunistic moulds such as Aspergillus, Penicillium, Scedosporium and Phaeoacremonium Essakhi et al, 2008;Gilgado et al, 2005;Mostert et al, 2005;Serra & Peterson, 2007;Staab et al, 2009). It is also well documented that translation elongation factor is the best marker for species identification in Fusarium (Geiser et al, 2004;O'Donnell, 2000).…”

Effect of Water Activity and Titania P25 Photocatalyst on Inactivation of Pathogenic Fungi - Contribution to the Protection of Public Health

“…and Scedosporium sp. cause human scedosporiosis, a fungal disease difficult to treat with a high mortality rate (16,17).…”