CSP typing in multi-azole resistant Aspergillus fumigatus isolates

S.M.T. Camps, E. Snelders, P.E. Verweij, W.J.G. Melchers

Author address: 

Radboud University Medical Center, NIJMEGEN, The Netherlands

Abstract: 

Objectives: We have recently described the emergence of multi-azole resistant Aspergillus fumigatus isolates in the Netherlands. The dominant resistance mechanism found was a point mutation in the cyp51A gene resulting in a substitution of leucine for histidine at codon 98 (L98H) in combination with a 34 base pair tandem repeat (TR) in the promoter region of this gene. The emergence of this single resistance mechanism suggests that the resistant isolates have a common evolutionary origin. Moreover, resistant A. fumigatus isolates were obtained from patients who never received azole treatment and this TR/L98H resistance mechanism was also present in environmental isolates of A. fumigatus, indicating that this resistance mechanism might not be induced in the patient but may have been evolved in the environment. CSP (gene encoding for a putative Cell Surface Protein) typing is a reliable, simple, rapid and discriminatory typing tool to genotype A. fumigatus isolates. Recently, a nomenclature system was proposed resulting in the classification of 18 CSP types. We used this method to type azole susceptible and TR/L98H resistant A. fumigatus isolates of clinical and environmental origin to investigate the genetic relatedness of multi-azole resistant isolates. Methods: Resistant isolates were identified by in vitro susceptibility testing. The resistance mechanism was subsequently determined by sequencing the cyp51A gene and its promoter region. From 30 isolates containing the TR/L98H resistance mechanism the CSP gene was sequenced. In addition, the CSP of 24 susceptible strains without TR/L98H alterations was sequenced. The sequences were subsequently assigned to one of the 18 CSP subtypes that were previously described. Results: The resistant isolates were grouped into three CSP types (2, 4B and 11). To each group clinical as well as environmental resistant strains were assigned. Susceptible isolates were classified to other CSP types than the resistant ones (1, 3, 4A, 5, 8, 13 and 14) except for one isolate belonging to CSP type 2. Conclusions: 1. Clinical and environmental multi-azole resistant (TR/L98H) isolates were grouped to the same CSP types so the TR/L98H resistance mechanism might not be induced in the patient but might be acquired from the environment. 2.The resistant A. fumigatus isolates were grouped to different CSP types than susceptible (wild type) isolates. This indicates that the isolates containing the TR/L98H alterations belong to a separate genetic A. fumigatus lineage.
2009

abstract No: 

04.1

Full conference title: 

4th Trends in Medical Mycology
    • TIMM 4th (2012)