Question

Microscopic difference between aspergillus flavus and fumigatus

Answer 1



Morphological effects of lipopeptides against Aspergillus fumigatus correlate with activities against (1, 3)-beta-D-glucan synthase.

MB Kurtz, IB Heath, J Marrinan, S Dreikorn, J Onishi, C Douglas

Antimicrobial Agents and Chemotherapy 38 (7), 1480-1489, 1994

The lipopeptide antifungal agents, echinocandins, papulacandins, and pneumocandins, kill Candida albicans by inhibiting glucan synthesis. For this fungus, there is a good correlation of in vitro enzyme inhibition with in vitro assays of MICs. Semisynthetic lipopeptides such as cilofungin, LY303366, L-693,989, and L-733,560 have activity in vivo against Aspergillus infections but appear to be inactive in broth dilution in vitro tests (MICs,> 128 micrograms/ml). To understand how compounds which lack activity in vitro can have good in vivo activity, we monitored the effect of pneumocandins on the morphology of Aspergillus fumigatus and A, flavus strains by light microscopy and electron microscopy and related the changes in growth to inhibition of glucan synthesis. Pneumocandin B0 caused profound changes in hyphal growth; light micrographs showed abnormally swollen germ tubes, highly branched hyphal tips, and many cells with distended balloon shapes. Aspergillus electron micrographs confirmed that lipopeptides produce changes in cell walls; drug-treated germlings showed very stubby growth with thick walls and a conspicuous dark outer layer which was much thicker in the subapical regions. The rest of the hyphal tip ultrastructure was unaffected by the drug, indicating considerable specificity for the primary target. The drug-induced growth alteration produced very compact clumps in broth dilution wells, making it possible to score the morphological effect macroscopically. The morphological changes could be assayed quantitatively by using conventional broth microdilution susceptibility assay conditions. We defined the endpoint as the lowest concentration required to produce the morphological effect and called it the minimum effective concentration to distinguish it from the no-growth endpoints used in MIC determinations. The minimum effective concentration assay was related to inhibition of glucan synthase activity in vitro and may provide a starting point for development of susceptibility testing methods for lipopeptides.

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Differences in pathogenicity and clinical syndromes due to Aspergillus fumigatus and Aspergillus flavus

Alessandro C Pasqualotto

Medical mycology 47 (Supplement_1), S261-S270, 2009

Most of the information available about Aspergillus infections has originated from the study of A. fumigatus, the most frequent species in the genus. This review aims to compare the pathogenicity and clinical aspects of Aspergillosis caused by A. fumigatus an A. flavus. Experimental data suggests that A. flavus is more virulent than A. fumigatus. However, these were mostly models of disseminated Aspergillusinfection which do not properly mimic the physiopathology of invasive aspergillosis, a condition that is usually acquired by inhalation. In addition, no conclusive virulence factor has been identified for Aspergillus species. A. flavus is a common cause of fungal sinusitis and cutaneous infections. Chronic conditions such as chronic cavitary pulmonary aspergillosis and sinuses fungal balls have rarely been associated with A. flavus. The bigger size of A. flavus spores, in comparison to those of A. fumigatus spores, may favour their deposit in the upper respiratory tract. Differences between these species justify the need for a better understanding of A. flavusinfections.