Phenotypic characteristics of isolates of Aspergillus section Fumigati from different geographic origins and their relationships with genotypic characteristics

Abstract

Background: Epidemiological studies worldwide have shown that A. fumigatus exhibits important phenotypic and genotypic diversity, and these findings have been of great importance in improving the diagnosis and treatment of diseases caused by this fungus. However, few studies have been carried out related to the epidemiology of this fungus in Latin America. This study's aim is to report on the epidemiology of the fungus by analyzing the phenotypic variability of Aspergillus section Fumigati isolates from different Latin American countries and the relationship between this variability, the geographical origin and genotypic characteristics.

Methods: We analyzed the phenotypic characteristics (macro- and micromorphology, conidial size, vesicles size, antifungal susceptibility and thermotolerance at 28, 37 and 48°C) of A. section Fumigati isolates from Mexico (MX), Argentina (AR), Peru (PE) and France (FR). The results were analyzed using analysis of variance (ANOVA) and Tukey's multiple comparison test to detect significant differences. Two dendrograms among isolates were obtained with UPGMA using the Euclidean distance index. One was drawn for phenotypic data, and the other for phenotypic and genotypic data. A PCoA was done for shown isolates in a space of reduced dimensionality. In order to determine the degree of association between the phenotypic and genotypic characteristics AFLP, we calculated the correlation between parwise Euclidean distance matrices of both data sets with the nonparametric Mantel test.

Results: No variability was found in the macromorphology of the studied isolates; however, the micromorphology and growth rate showed that the PE isolates grew at a faster rate and exhibited the widest vesicles in comparison to the isolates from MX, AR and FR. The dendrogram constructed with phenotypic data showed three distinct groups. The group I and II were formed with isolates from PE and FR, respectively, while group III was formed with isolates from MX and AR. The dendrogram with phenotypic and genotypic data showed the same cluster, except for an isolate from FR that formed a separate cluster. This cluster was confirmed using PCoA. The correlation between the phenotypic and genotypic data of the isolates revealed a statistically significant association between these characteristics.

Conclusions: The PE isolates showed specific phenotypic characteristics that clearly differentiate them from the rest of the isolates, which matches the genotypic data. The correlation between the phenotypic and genotypic characteristics showed a statistically significant association. In conclusion, phenotypic and genotypic methods together increase the power of correlation between isolates.

Figure 1

Scanning Electron Microscopy of the phenotypic characteristics of A. section Fumigati isolates selected from each country. Conidia size (a); vesicles size (b) and growth rate (c). The samples were processed with a conventional technique for SEM. Abbreviations: AR-Argentina; MX-Mexico; FR- France and PE-Peru.

Figure 2

Dendrogram based on phenotypic data (conidia and vesicle size and thermotolerance), generated by UPGMA using Euclidean distances (r = 0.89859, P = 0.0004) of A. section Fumigati isolates from MX, AR, FR and PE. The number on the nodes represents the support values based on 10,000 bootstrap replicas.

Figure 3

Dendrogram based on phenotypic (conidia and vesicle size and thermotolerance) and genotypic data (AFLP), generated by UPGMA using Euclidean distances (r = 0.78763, P = 0.0004) of 55 A. section Fumigati isolates from MX, AR, FR and PE. The number on the nodes represents the support values based on 10,000 bootstrap replicas.

Figure 4

Principal coordinates analysis (PCoA) of pheno and genotypic data of 55 A. section Fumigati isolates from MX, AR, FR y PE in a multidimensional space.