Microsatellite typing to trace Aspergillus flavus infections in a hematology unit

Abstract

Assessing the relatedness of strains isolated from patients and their environment is instrumental in documenting the source of preventable health care-associated life-threatening Aspergillus flavus human infection clusters. The present study aimed at identifying and selecting suitable microsatellite markers for A. flavus typing. This typing scheme was then applied to investigate the A. flavus epidemiology within a hematology unit in Sfax, Tunisia. Use of a combination of five markers made it possible to discern clusters of isolates and to substantiate the genetic diversity of A. flavus within clusters. Isolates from Tunisia and Marseille, France, displayed distinct haplotypes, indicating a highly significant geographical structuring of A. flavus. The typing of clinical and environmental A. flavus isolates in a hematology unit provided insights into its hospital epidemiology. From a heterogeneous genetic background, a cluster indicative of a clonal propagation episode within the unit could be identified. In two patients with invasive aspergillosis, the same genotype was found in clinical and environmental isolates, indicating hospital-acquired colonization and infection. In further studies, this novel microsatellite typing scheme might be instrumental in illuminating important epidemiological issues about A. flavus population genetics or epidemiology, including tracing the sources and routes of transmission.

FIG. 1.

Distribution frequency of microsatellites in A. flavus genome.

FIG. 2.

Allele size distribution of A. flavus at 12 microsatellites upon analysis of 15 isolates from Marseille (hatched bars) and 48 isolates from Tunisia (black bars). x axis, number of isolates; y axis, allele size.

FIG. 3.

Neighbor-joining dendrogram based on the Dice similarity coefficient upon analysis of five microsatellite makers in 48 A. flavus isolates from a hematology ward in Tunisia. The isolates are identified by the isolate number followed by the patient number (P1 to P15). The isolates are described in Table 1. The highlighted isolates from three patients and their environment illustrate two epidemiological scenarios: for P1 (square with solid-line border), each isolate (clinical and environmental) has a distinct genotype, indicating exposure to a genetically highly heterogeneous A. flavus population; for P2 (square with dashed-line border) and P8 (square with dotted-line border), clinical and environmental isolates share the same genotype, indicating exposure to a clonal A. flavus population.