Research & Development

Taxonomy of Aspergillus flavus complex
Aspergillus section flavi is said to be comprised of a group of 25 species. The phylogeny of 25 isolates (10 reference and 15 clinical) belonging to the Aspergillus section flavi was to be ascertained based on three genes sequences; O –methyltransferase (OMT), β-tubulin, and the Internal Transcriber Regions and 5.8S rDNA. Fifteen clinical isolates were to be identified as species from the section flavi based on the three gene sequences and also more detailed morphology (microscopic and macroscopic) and susceptibility profiles.
Phylogenetic trees for ITS and β-tubulin showed similar topology and most clinical isolates grouped with A. flavus and A. oryzae but most reference isolates grouped separately. The OMT gene showed three distinct groups and differentiated A. flavus and A. oryzae. The combined tree showed isolates to be separated into an A. flavus ‘clade’ and ‘A. oryzae ‘clade’.
Macroscopic observations revealed five groups. Eleven clinical isolates grouped with A. toxicarius, but many of the reference isolates and three clinical isolates showed the most distinct colonial morphology.
Susceptibility profiles showed isolates to be classified into six groups, with eight clinical and four reference isolates fully susceptible but seven isolates were intermediate to voriconazole (VRZ) only. Six isolates showed resistance; one to itraconazole, three to amphotericin B and three to VRZ (one isolate was AMB and VRZ resistant). 
Clinical isolates could not be identified to be the same as any of the reference species by any of the three methods, but they could be grouped together based on similarities to the reference species and each other.
Further work will focus on the completion of phylogenetic trees to include isolates that could not be amplified with current primers and also the inclusion of more reference isolates may assist regarding the identities of the clinical isolates.