Aim: Chronic pulmonary aspergillosis (CPA) is an uncommon but progressive pulmonary disease estimated to affect about 3,600 patients in the UK, causing significant mortality. The main causal organism, Aspergillus fumigatus, is an ubiquitous environmental, opportunistic fungus, and exposure is by inhalation of its abundant airborne conidia. Long-term antifungal treatment required in CPA is hampered by the rising frequency of triazole resistance in A. fumigatus isolated in UK patients. Little is known about the genetic diversity of clinical A. fumigatus isolates from CPA patients in the UK and less about the relationship between genetic relatedness and azole resistance. The aim of our study was to identify the geographical distribution of genotypes in clinical A. fumigatus isolates from CPA patients in the UK and compare two tandem repeat-based typing methods: nSTRAf, based on a panel of nine STR markers, and TRESP, a sequencing method based on a panel of long tandem repeats in three surface protein coding genes, cell surface protein A (CSP), antigenic galactomannan protein (MP-2), and a hypothetical protein with a CFEM domain (CFEM). In addition to assessing their ability to discriminate, we investigated whether typing could determine if genotype was associated with azole resistance.
Methods: A total of 31 A. fumigatus isolates collected from 14 CPA patients located in different regions of the UK were tested by both typing methods. Cluster analysis was performed using NCSS 11 software. Our data were compared with an additional 175 TRESP and 137 nSTRAf results using RAxML software (randomized accelerated maximum likelihood).
Results: A total of 23 and 18 genotypes were identified by nSTRAf and TRESP, respectively. A wide geographical distribution among these genotypes was seen across the UK. The pattern of genetic diversity contrasted between some patients being colonised by multiple genotypes while other patients harboured a single genotype over a number of years. All genotyping, except for one pair of isolates, showed concordance between the nSTRAf and TRESP typing methods, with the latter method showing slightly higher discriminatory power. However, genotypes did not reflect resistance profiles.
Conclusion: This study showed large genetic diversity in the clinical isolates tested and suggests a wide geographical distribution of A. fumigatus genotypes in the UK, some not previously reported and distinct from Spanish and Portuguese isolates. There were no instances of a single genotype spread widely throughout the UK, although more analysis is required. In some patients, azole resistance appeared to be related to treatment-induced selection pressure, while in others, colonisation was with multiple genotypes. The nSTRAf method offered better discrimination and could be the appropriate option for centres with the availability of funding for highly technical services and trained staff.
Full conference title:
- AAA 8th (2018)