Typing by irnrnunoblot of Aspergillus fumigatus from nosocornial infections

Phenotypic and genotypic characterization of reference strains of the genus Aspergillus

Twenty-five culture collection strains from four Aspergillus species (A. fumigatus n = 8, A. flavus n = 8, A. niger n = 4, A. nidulans n = 5) were characterized by four methods: (i) determination of patterns in an assimilation assay; (ii) protein pattern of whole mycelial cell lysates in the sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis (PAGE); (iii) reactivity of a pool serum obtained from cystic fibrosis patients with mycelial lysates in the immunoblot; and (iv) random amplification of polymorphic DNA (RAPD) with eight primers having arbitrary or repetitive sequences. In the assimilation assay the A. fumigatus strains showed identical patterns in contrast to the strains of the species A. flavus, A. niger, and A. nidulans, which each showed four patterns. In the SDS-PAGE no differences in the band patterns in the A. fumigatus strains were found, in contrast to the A. flavus (three patterns), A. nidulans (five patterns) and A. niger strains (two patterns). The immunoblot patterns were characteristic for each species with bands at 62 and 17/18 kDa in the A. fumigatus strains, at 51 and 18 kDa in the A. flavus strains, at 51 kDa in the A. niger strains, and at 51, 40 and 17/18 kDa in the A. nidulans strains allowing, however, no intraspecies typing. In the RAPD assay four out of eight primers gave interpretable patterns with 3-20 bands. None of the primers showed sufficient discriminatory power when used alone. However, when combining the results of two of the primers (5'-GTA TTG CCC T-3' and 5'-GAT AGA TAG ATA GAT A-3') all strains except two A. fumigatus strains could be clearly separated from each other. It is concluded that the the RAPD assay showed the most discriminatory power in all Aspergillus species investigated. In contrast to the phenotypically similar A. fumigatus strains, the strains of the species A. flavus, A. nidulans and A. niger differed in their phenotypic characteristics. The presented data of strains from international culture collections may serve as basis for interlaboratory standardization of typing methods.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Epidemiology of nosocomial fungal infections

This paper briefly reviews the current knowledge of the epidemiology and modes of transmission of nosocomial fungal infections and some of the therapeutic options for treating these diseases. In the mid-1980s, many institutions reported that fungi were common pathogens in nosocomial infections. Most, if not all, hospitals care for patients at risk for nosocomial fungal infections. The proportion in all nosocomial infections reportedly caused by Candida spp. increased from 2% in 1980 to 5% in 1986 to 1989. Numerous studies have identified common risk factors for acquiring these infections, most of which are very common among hospitalized patients; some factors act primarily by inducing immunosuppression (e.g., corticosteroids, chemotherapy, malnutrition, malignancy, and neutropenia), while others primarily provide a route of infection (e.g., extensive burns, indwelling catheter), and some act in combination. Non-albicans Candida spp., including fluconazole-resistant C. krusei and Torulopsis (C.) glabrata, have become more common pathogens. Newer molecular typing techniques can assist in the determination of a common source of infection caused by several fungal pathogens. Continued epidemiologic and laboratory research is needed to better characterize these pathogens and allow for improved diagnostic and therapeutic strategies.

Multicentric epidemiological study of Aspergillus fumigatus isolates by multilocus enzyme electrophoresis

The genotypes of 63 isolates of Aspergillus fumigatus obtained from three hospitals in different geographical areas and of eight culture collection strains were determined by multilocus enzyme electrophoresis. Twelve of the 17 enzymatic loci studied were polymorphic, giving rise to 48 different electrophoretic types. The existence of fixed multilocus genotypes, significant heterozygote deficits and excesses at the different loci, and linkage disequilibria within subpopulations strongly suggests a clonal reproduction mode for A. fumigatus. Numerical analysis of the comparison and disposition of the different electrophoretic types demonstrates a significant genetic differentiation between the three sampling sites. However, no correlation could be found between geographical distances and genetic differentiation. On account of the multiple discriminatory markers, multilocus enzyme electrophoresis typing seems to be a very powerful tool for epidemiological and reproductive mode studies of A. fumigatus.

Use of phenotypic and genotypic fingerprinting methods in the strain identification of Aspergillus fumigatus

Aspergillus fumigatus isolates (n = 6) from a lung transplant recipient, one isolate from a patient who had been on the same ward and a reference strain (NCPF 2140) were compared using three typing methods: SDS-PAGE, immunoblotting with serum from the transplant patient and random amplified polymorphic DNA (RAPD) assay. Neither the SDS-PAGE, immunoblot nor RAPD assay with single primers revealed differences between the eight isolates. Digestion of one primer product with the endonuclease EcoRI discriminated between the six patient isolates and the other two strains. The RAPD assay using pairwise combined primers showed identical patterns for the patient's strains but differentiated between the two other strains. It is concluded that any single technique may fail to detect strain differences and that a spectrum of typing methods is necessary in order to reveal or to exclude cross-infections with Aspergillus fumigatus.

DNA typing of epidemiologically-related isolates of Aspergillus fumigatus

Invasive aspergillosis is often nosocomially acquired and carries a high mortality. Molecular typing methods to discriminate isolates have now been developed. Using simple restriction endonuclease (Sal1 and Xho1) digestion of total genomic DNA, we have typed 25 epidemiologically-related isolates of A. fumigatus from six hospital episodes of invasive aspergillosis. Eight DNA types were found and in each case the DNA type matched precisely the epidemiological data. Thus DNA typing of A. fumigatus can provide the means to match isolates from linked sources and distinguish isolates from diverse origins.