Species Distribution and In Vitro Azole Susceptibility of Aspergillus Section Nigri Isolates from Clinical and Environmental Settings

Abstract

Aspergillus section Nigri includes species of interest for animal and human health, although studies on species distribution are limited to human cases. Data on the antifungal susceptibilities and the molecular mechanism of triazole resistance in strains belonging to this section are scant. Forty-two black Aspergillus strains from human patients (16 isolates), animals (14 isolates), and the environment (12 isolates) were molecularly characterized and their in vitro triazole susceptibilities investigated. Aspergillus tubingensis was isolated from humans, animals, and environmental settings, whereas Aspergillus awamori and Aspergillus niger were isolated exclusively from humans. Phylogenetic analyses of ␤-tubulin and calmodulin gene sequences were concordant in differentiating A. tubingensis from A. awamori and A. niger. Voriconazole and posaconazole (PSZ) were the most active triazoles. One A. tubingensis strain was resistant to itraconazole and PSZ and one A. niger strain to PSZ. Sequence analysis of the cyp51A gene revealed different sequence types within a species, and A. tubingensis strains were also phylogenetically distinct from A. awamori/A. niger strains according to the strain origin and susceptibility profile. Genetic analysis of the cyp51A sequences suggests that two nonsynonymous mutations resulting in amino acid substitutions in the CYP51A protein (changes of L to R at position 21 [L21R] and of Q to R at position 228 [Q228R]) might be involved in azole resistance. Though azole resistance in black Aspergillus isolates from animals and rural environments does not represent a threat to public health in Southern Italy, the use of triazoles in the clinical setting needs to better monitored. The cyp51A sequence is useful for the molecular identification of black Aspergillus, and point mutations in protein sequences could be responsible for azole resistance phenomena.

New Insights into the Cyp51 Contribution to Azole Resistance in Aspergillus Section Nigri

“…Both ITC and VRC exhibited good in vitro activity, even though low susceptibility to VRC was more common than to ITC, which is also in line with previous results (26). In addition, ITC non-wt isolates were found more frequently among A. tubingensis isolates than in the other species of this section that we tested, as already described (23,26,27). In accordance with previous works (23,27), crossresistance was not common in our isolates.…”

“…The three azoles tested here (VRC, PSC, and ITC) showed good activity, with POS being the most active one, a finding in accordance with previous studies (23)(24)(25). The low modal POS MIC and its narrow MIC range are also indicative of its elevated in vitro activity against these fungi.…”

Drug Sensitivity and Resistance Mechanism in Aspergillus Section Nigri Strains from Japan

“…Our finding suggests that A. tubingensis isolates are intrinsically resistant to azoles, but this does not depend on exposure to azoles. Several reports from other countries, so far, have supported the idea of less susceptibility in A. tubingensis (6,7,9,21). Considering the lowered azole susceptibilities in A. tubingensis, it must be further stressed that identification of the detailed species causing mycoses is important for appropriate drug therapy.…”

“…2). We , N506H 63253 1 1 K477E 49719 1 2 54606 1 2 V383L 54634 1 2 V383L 55451 1 2 K477E 55743 1 2 F343L, L511F 56814 1 2 V383L 62616 1 2 F343L, L511F 62621 1 2 V383L 63657 1 2 V383L 54679 2 2 K477E 57144 2 2 F343L, L511F 62255 2 2 V383L 62617 2 2 V383L 63332 2 2 D474N, N506H 63348 2 2 F343L, L511F 63878 2 2 V383L 63879 2 2 V383L 63880 2 2 D474N, N506H 63881 2 2 L157I, G509E 63882 2 (4,(7)(8)(9). MIC distributions of antifungals showed obvious differences between clinical isolates and environmental isolates for 5FC, where the clinical isolate group showed higher MICs than the environmental isolate group.…”

“…Importantly, several reports on the antifungal drug susceptibility of strains of Aspergillus section Nigri have revealed that strains showing higher MICs of itraconazole were often isolated from A. niger and A. tubingensis in a clinical setting as well as from the environment (6)(7)(8)(9). This is suggestive of an intrinsic resistance to itraconazole by these species.…”