Fungal biomass is a key factor affecting polymorphonuclear leukocyte-induced hyphal damage of filamentous fungi

Abstract number: O449

Antachopoulos C., Demchok J., Roilides E., Walsh T.

Objectives: Previous studies of polymorphonuclear leukocyte (PMN)-induced hyphal damage (HD) of filamentous fungi have used the effector-target (E:T) ratio as the only variable for assessment or comparison of results. However, we hypothesised that the overall hyphal biomass of organism may also be an important determinant in host-pathogen interaction. We therefore investigated the effect of fungal biomass on PMN-induced HD.

Methods: An inoculum of 2×104 conidia/ml of one isolate each of Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Rhizopus oryzae, Rhizopus microsporus, Cunninghamella bertholletiae, Scedosporium prolificans and Fusarium solani was incubated for 6 one- to two-hourly different time periods in order to yield biomass values ranging between 0.01–0.1 optical density (OD, measured at 405 nm). PMNs from healthy volunteers were then added at E:T ratios of 5:1, 10:1, 20:1, 50:1 and 100:1, and HD was assessed by XTT metabolic assay. For each E:T ratio, the relationship between HD and OD was studied using nonlinear regression analysis.

Results: HD decreased with increasing biomass following a sigmoid pattern described with the Emax model (median R2: 0.87). HD at 0.01 OD exceeded HD at 0.1 OD (P < 0.01 for all E:T ratios) by >2-fold in 64 of 80 comparisons (8 isolates x 5 E:T ratios x 2 replicate experiments). The sigmoid curves were shifted to the right with higher E:T ratios; the EC50 values (i.e., the model-derived OD at which HD is reduced half-way between the maximum and minimum HD values for a given E:T ratio and isolate) obtained for 50:1 or 100:1 were higher than those obtained for 5:1 (P < 0.01). Using the same E:T ratio, interspecies differences were observed; for 5:1, lower EC50 values were obtained for A. flavus and the three zygomycete species.

Conclusion: PMN-induced HD decreases with increasing biomass at rates that are species-dependent and that decrease with higher E:T ratios. This biomass effect may have important implications for understanding systemic host defences and can be a useful factor in the design and interpretation of studies of PMN-induced HD of filamentous fungi.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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