Background: Penicillium is one of the most common fungi and has an important economic impact on human life. Some of its species have been described as causal agents of human and animal infections, P. marneffei being the most clinically significant species able to cause fatal mycosis in immunocompromised patients. In recent years, the taxonomic structure of the genus Penicillium has changed dramatically using different molecular approaches, with a notable increase in the number of species placed into the genus. Moreover, species like P. marneffei and other human opportunistic pathogens like P. piceus, P. purpurogenus and P. radicus have been transferred to the genus Talaromyces. Since these taxonomical changes, therefore, the diversity of Penicillium species associated to clinical specimens using molecular techniques has not yet been explored. The aim of this study was to characterize molecularly a large set of clinical isolates identified morphologically as belonging to the genus Penicillium and to establish the in vitro antifungal susceptibility profile for the most frequently identified species.
Material/methods: A total of 100 isolates previously identified as Penicillium sp. were received from the Fungus Testing Laboratory at the University of Texas Health Science Center in San Antonio (USA). The isolates were studied phenotypically using standard growth conditions. Molecular identification was made using two genetic markers, the internal transcribed spacer (ITS) and a fragment of the β-tubulin gene (BenA). In order to assess phylogenetic relationships, maximum likelihood and bayesian inference assessments were used. Antifungal susceptibility testing was determined according to CLSI document M38-A2 for amphotericin B (AMB), voriconazole (VRC), itraconazole (ITC), posaconazole (PSC), terbinafine (TRB), anidulafungin (AFG), caspofungin (CFG), micafungin (MFG) and 5-fluorocytosine (5FC).
Results: The isolates identified belonged to 74 Penicillium, 24 Talaromyces and two Rasamsonia. For the genus Penicillium, 23 species distributed into ten sections were recognized, P. rubens and P. citrinum being the most frequently identified taxa. In Talaromyces, ten species belonging to four sections were identified, where T. amestolkiae and T. purpurogenus were the most prevalent ones. Likewise, the two isolates of Rasamsonia were identified as R. argillacea. TRB was the most active drug, whereas 5FC showed the lowest in vitro activity against the species tested.
Conclusions: This study is the first to characterize a large number of clinical isolates of Penicillium and to demonstrate a wide range of species associated to clinical specimens. Because of the difficulties in recognizing species of the genera that share penicilium-like morphs using morphological criteria alone, molecular identification is crucial to avoid wrong identifications for clinical diagnosis. Susceptibilities of the isolates to nine antifungal drugs in vitro showed mostly high MICs, except for TRB.
Full conference title:
- ECCMID 26th (2016)