Year: 2020
Type: review
Abstract: The complexity and diversity of microbial colony morphologies have contributed to the identification of pathogenic microbes for decades.Even as biomarker-based approaches are adopted for diagnosis of fungal infections, culture-based methods remain valuable for the identification of specific etiological agents and determination of antifungal susceptibility [1].Thus, when obtainable, infectious organisms are observed as macroscopic colony biofilms in clinical settings.We define macroscopic morphologies (a strain's morphotype) as the collective phenotypes of form and/or structure attributed to a group of organisms of the same species within a defined area such as a colony.Clinical isolates of Aspergillus fumigatus, Cryptococcus neoformans, and Candida spp.have been reported for decades to be morphologically variable within and between patients [2-4].Similarly, diverse population-level macroscopic morphologies of bacterial pathogens have been observed in clinical samples [5,6].A key question is whether observed microbial morphotypes tell us anything about their virulence.Below, we discuss the intrinsic and extrinsic factors that contribute to macroscopic morphological variation in fungi and bacteria.We then discuss fungal and bacterial examples linking macroscopic morphology with virulence and the challenges faced with studying this relationship.Finally, we discuss the importance of investigating recurring and distinct fungal macroscopic morphologies for furthering our understanding of host-fungal interactions. What features of population-level growth contribute to macroscopic morphologies?Microbial populations are most often observed as macroscopic colonies with defined morphologies on a solid surface.Underlying features of macroscopic microbial colonies include the production and secretion of extracellular matrix (ECM) [7], quorum sensing [8], surface appendages [9], pigmentation [10,11], and cellular morphology [12].Importantly, these features often, but not always, impact a given strain's macroscopic morphology.For example, quorum sensing in Pseudomonas aeruginosa regulates the production of phenazines that, under permissive conditions, contribute to colony pigmentation and topography [8].The production of the long filamentous pilus is reflected in the colony morphology of Neisseria gonorrhoeae, in which colonies without a pilus are flat and lack a distinct colony edge [9].However, while some features may broadly impact microbial colony morphologies, others are speciesspecific.For example, the ECM of Vibrio cholerae is necessary for the rugose colony morphology [7], but in the pathogenic filamentous fungus A. fumigatus, loss of the primary ECM component galactosaminogalactan does not impact colony morphology [13].
Source: PLoS Pathogens
Authors: Caitlin H. Kowalski, Robert A. Cramer
Institution: Dartmouth College
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $2,500
OpenAlex ID: W3035945100