Universal In Vitro Antifungal Resistance of Genetic Clades of the Fusarium solani Species Complex

Abstract

Eleven antifungal drugs were tested against representative isolates of the four phylogenetic clades of the Fusarium solani species complex obtained in a multilocus sequence analysis. They all showed very poor activity, with no differences among the clades. Amphotericin B was the most active drug.Fusarium solani is a fungus that is widely distributed in nature and is able to produce many plant diseases with important economic impacts and, also, severe, usually fatal, human infections (7,9,15,23). These infections can be characterized by their resistance to practically all available antifungal drugs (3,21,24). Primary therapy with voriconazole (VRC) or a lipid formulation of amphotericin B (AMB) is currently recommended (22). Although the response of Fusarium spp. to AMB is poor in general, it depends on the species involved, with F. solani being the most resistant species, at least in vitro (24). Recently, Zhang et al. (29) used a multilocus sequence analysis approach to demonstrate that under the generic name F. solani, at least 45 phylogenetically distinct species exist, most of which have not been described formally. It is unknown if antifungal susceptibility varies among these phylogenetic species. If such differences exist, knowing them could be useful for guiding clinical treatments. Due to the difficulties of testing representative strains of all the phylogenetic species, we tested isolates belonging to the four major clades, inferred from a combined phylogenetic analysis of fragments of three genes, i.e., the translation elongation factor 1␣ (EF-1␣) and ␤-tubulin genes and the internal transcribed spacer (ITS) of the nuclear rRNA gene, against traditional and new antifungal drugs.Fifty isolates from clinical or environmental sources, morphologically identified as F. solani (6), were included in the study (Table 1). Isolates were stored by lyophilization and submerged in slant cultures in mineral oil at room temperature. The procedures for DNA extraction, amplification, and sequencing of the different regions analyzed were described by Gilgado et al. (8). The annealing temperature was 55°C, and the primers used were EF-1H and EF-2T (16) for EF-1␣, TUB-F (5) and T22 (17) for ␤-tubulin, and ITS5 and ITS4 (28) for the ITS. The phylogenetic analysis was performed using PAUP*, version 4.0b10 (27). Maximum parsimony trees were obtained after 100 heuristic searches with random sequence addition and tree bisection-reconnection branch-swapping algorithms, collapsing zero-length branches, and saving of all minimal-length trees (MulTrees). The results of the partition homogeneity test showed that the three locus sequence data sets were congruent (P ϭ 0.2) and could therefore be combined. Sequences of the three genes were analyzed phylogenetically as separate (data not shown) and combined data sets.We evaluated the in vitro activities of 11 antifungal drugs against 27 representative strains (22 clinical and 5 environmental) randomly chosen from the main clades obtained in the phylogenetic analysis. The isolates were g...

Emergence of fusarioses in a university hospital in Turkey during a 20-year period

“…Species-specific differences in the susceptibility of Fusarium isolates was apparent in the MICs to amphotericin B, voriconazole, and posaconazole. In agreement with previous reports [16,37], amphotericin B was the most effective agent across all isolates. The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and the European Confederation of Medical Mycology (ECMM) recommend amphotericin B and voriconazole as the first optional agents in the treatment of cases with fusariosis [18].…”

“…However, in the present study, these compounds were not effective against some of the species, sometimes indicating high degrees of intraspecific variability (Table 4). Some studies have reported that the MIC values in F. verticillioides were high for amphotericin B and low for posaconazole [16,37]. Similarly, we also observed activity of posaconazole against this species, but with a limited degree of confidence.…”

“…Most opportunistic Fusarium species are relatively to very resistant to antifungal drugs in vitro, although anti-fungal sensitivity profiles may differ between species [2,16,17]. While refractory onychomycoses are not life-threatening, timely and effective treatment for deep and disseminated fusariosis is very important.…”

“…While refractory onychomycoses are not life-threatening, timely and effective treatment for deep and disseminated fusariosis is very important. Joint guidelines on the treatment of hyalohyphomycoses recommend amphotericin B and voriconazole for the treatment of systemic fusariosis [18], despite variable minimum inhibitory concentration (MIC) test results for both drugs [2,16,17,19]. Hence, accurate identification of the species involved is of importance for epidemiological studies and for guiding clinical follow-up of the patients [2,13].…”

Accurate and Practical Identification of 20 Fusarium Species by Seven-Locus Sequence Analysis and Reverse Line Blot Hybridization, and an In Vitro Antifungal Susceptibility Study

“…In humans, they cause infections ranging from superficial disease (e.g., keratitis and onychomycosis) to life-threatening disseminated infections; the latter occur predominantly in severely immunocompromised patients (7,18,19) in whom mortality approaches 100% (10). This high mortality is due in part to frequent delays in diagnosis and to the fact that most Fusarium species, particularly those nested within the Fusarium solani species complex (FSSC), are typically resistant to most antifungal agents (1,2,28).…”