Diversity and origins of Indian multi‐triazole resistant strains of Aspergillus fumigatus

Abstract

Aspergillus fumigatus is a widespread opportunistic fungal pathogen causing an alarmingly high mortality rate in immunocompromised patients. Nosocomial infections by drug-resistant A. fumigatus strains are of particular concern, and there is a pressing need to understand the origin, dispersal and long-term evolution of drug resistance in this organism. The objective of this study was to investigate the diversity and putative origins of triazole resistance of A. fumigatus from India. Eighty-nine isolates, including 51 multiple triazole resistant (MTR) isolates and 38 azole-susceptible isolates, were genotyped using multilocus sequence typing (MLST), mating typing and PCR fingerprinting. MLST resolved the 51 MTR isolates into three genotypes, two of which have susceptible counterparts, suggesting that MTR isolates originated multiple times in India. The multiple-origin hypothesis was further supported by the diversity of sequences at the triazole target gene CYP51A among the MTR isolates, and by PCR fingerprints. Interestingly, there is abundant evidence for mating and recombination in natural population of A. fumigatus in India, suggesting that sexual spread of TR34 /L98H, the dominant MTR allele, is possible. Our results call for greater attention to MTR in A. fumigatus and for better management of antifungal drug use.

Evidence of unique genetic diversity in Aspergillus fumigatus isolates from Cameroon

“…Our analyses identified significant novel allelic and genotypic diversities in that region. Interestingly, unlike the low genetic differentiation among geographic populations of A. fumigatus from other geographic regions from Eurasia and North America, the Cameroonian sample of A. fumigatus was significantly differentiated from regional populations analysed so far from other parts of the world. Whilst our analyses revealed abundant evidence of clonal reproduction, we identified a notably diverse sub‐population in Eloundem that was differentiated from other local populations within Cameroon and this sub‐population had signatures of recombination.…”

“…Generally speaking, a genetically differentiated population can be due to multiple factors including natural selection, genetic drift and mating patterns. For instance, the Indian population of A. fumigatus was significantly differentiated from other geographic populations largely due to the selective sweep of a multiple triazole‐resistant microsatellite genotype across India . While assumed to be neutral, the microsatellite loci used in this study, which are identical to those used in the Indian study, might be linked to genes under selective constraints.…”

“…Given the mobile nature of asexual A. fumigatus spores and the finding of triazole resistant strains elsewhere in Africa and outside of Africa, we expected that triazole resistance might be present in the Cameroonian environment. In addition, since A. fumigatus samples from most other geographic areas showed evidence for abundant gene flow at local, regional and continental scales, we also hypothesised that evidence for gene flow would be detected among local samples within Cameroon and between the Cameroonian samples and other geographic populations of A. fumigatus . Within Cameroon, the sampled regions were located relatively close to each other, closer than most of the reported regional samples from elsewhere that showed no genetic differentiation.…”

“…Previous studies have shown that geographic populations of A. fumigatus often consist of genetically diverse strains . For instance, Klaassen and colleagues found up to five genetically differentiated A. fumigatus clusters in the Netherlands .…”

Clinical implications of globally emerging azole resistance in Aspergillus fumigatus

“…However, a striking exception to this pattern was shown in India, where isolates containing TR 34 /L98H were found to be highly related despite being isolated from both clinical and environmental sources across more than 1000 km. This high degree of relatedness across India suggested a recent selective sweep of a highly fit genotype that is associated with the TR 34 /L98H allele [73,74]. We found that the isolates that we sequenced all show the hallmarks of genetic recombination, showing that azole-resistant alleles are segregating into diverse genetic backgrounds.…”