Growth of Aspergillus fumigatus is inhibited by Candida species on sealed Sabouraud agar plates, but not on sealed Columbia agar plates
Abstract number: 902_p1781
Randhawa et al. (1) reported that some Candida species inhibit growth of Aspergillus fumigatus when cocultured on pepton-glucose agar (PGA), especially on sealed agar plates. C. glabrata and C. albicans proved to be the major inhibitors in this study. The authors speculate that colonisation by Candida species may delay a definite diagnosis of aspergillosis from sputum or other clinical specimens. To assess the possible impact of these findings for clinical diagnostics of A. fumigatus, we questioned the role of used media.
The experiments of Randhawa et al. (1) were repeated with Sabouraud dextrose agar (SDA), Candida-II agar (C-II), Columbia agar (CA) and CLED agar on sealed and unsealed agar plates for cocultivation of A. fumigatus with C. albicans (six strains), C. glabrata (one strain), C. krusei (three strains) and C. tropicalis (three strains).
On SDA, growth of A. fumigatus was strongly inhibited by Candida species, especially on sealed plates. On unsealed plates, C. glabrata and C. albicans were strong inhibitors as well, whereas C. tropicalis and C. krusei were only weak inhibitors. After cocultivation with strong inhibitors for 48 to 72 h, no visible growth of A. fumigatus was obtained. These results were in concordance with those reported for PGA (1). There was no difference in growth inhibition between SDA and C-II.
In contrast, on CA, all tested Candida species were weak inhibitors on sealed plates. On unsealed plates, a relevant inhibition was registered for C. tropicalis and C. albicans, whereas C. glabrata and C. krusei were only weak inhibitors. After 48 to 72 h of cocultivation, visible growth of A. fumigatus was obtained, regardless of the tested Candida strain. Growth inhibition on CLED was comparable with that on CA.
To avoid contamination, sealed agar plates are often used for isolation of A. fumigatus in clinical laboratories. When specimens that might be heavily contaminated by Candida species are cultured on SDA, delayed growth or growth inhibition of Aspergillus might be a concern. Our results suggest that this problem might be overcome by simultaneous inoculation on a glucose-poor medium, e.g. CA plates, and prolonged incubation of these plates for more than 48 h.
|Session name:||XXIst ISTH Congress|
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