Real-time monitoring of fungal inhibition and morphological changes

Abstract

Mold growth constitutes a problem in many food and clinical environments and there is therefore focus on studying antifungal activity. Methods for determining growth inhibition by measuring colony growth or biomass are, however, time-taking and rapid methods for evaluation of antifungal effects are needed. Propionic acid and diacetyl are antifungal compounds produced by a range of dairy-associated bacteria. Their activity against Penicillium spp. was monitored real-time using an optical detection system with tilted focus plane to assess growth and morphological changes of Penicillium spp. by image recording inside a 96 well microplate. Images were used for generation of growth curves by using a segmentation and extraction of surface areas (SESA) algorithm and for quantifying morphology changes. Using image analysis growth could be detected within 15 h compared with more than 30 h when using standard optical density measurements. Induced morphological changes of fungi could furthermore be visualized and quantified using morphological descriptors such as circularity, branch points, perimeter and area of spores and growing hyphae. Propionic acid inhibited two out of two Penicillium spp. while morphological changes were strain dependent at the concentrations tested. Diacetyl inhibited six out of six Penicillium spp. strains and increased spore size and number of germination sites in two out of six of the strains prior to germination.

7‐hydroxytropolone is the main metabolite responsible for the fungal antagonism of Pseudomonas donghuensis strain SVBP6

“…S2). Similar phenotypes have been observed with other compounds of bacterial origin (Garbeva et al, 2014;Aunsbjerg et al, 2015;Torres et al, 2016;Melloul et al, 2018).…”

Interruption of Aspergillus niger spore germination by the bacterially produced secondary metabolite collimomycin

“…did not reach the polarized growth stage) after 14 h in the presence of Cf Ter331, the majority (89%) were no longer dormant but had entered the isotropic growth stage (Table ). Such an arrestment of fungal spores in the isotropic growth phase has been reported previously for other antifungal compounds, including olorofim (du Pré et al ., ), natamycin (van Leeuwen et al ., ) and diacetyl (Aunsbjerg et al ., ). Staining with fluorescein diacetate (FDA) showed (Table ) that the majority (83.0%) of the isotropically growing An N402 conidiospores in co‐cultures with Cf Ter331 were viable after 12 h, which was not significantly different from what was observed with isotropically growing spores in monoculture (86.2%) or in co‐culture with the collimomycin‐deficient mutant Cf Ter331∆col (81.8%).…”

Host-guest complexes of imazalil with cucurbit[8]uril and β-cyclodextrin and their effect on plant pathogenic fungi

“…Various methods have been used to monitor fungal growth and inhibition due to antifungal activity of chemical compounds. Although optical density (OD) has sometimes been used to determine the inhibitory activity of antifungal compounds, the disadvantage of using OD especially for filamentous fungi, however, is that actively growing hyphae are not evenly distributed and this might give uncertainties in the quantitative estimation of fungal growth 37 . In addition, sporulation might give unexpectedly high OD values and thereby overestimation of mycelial growth 37 .…”