Effect of silver nanoparticles on Candida albicans biofilms: an ultrastructural study
Authors: Jose L Lopez-Ribot
Dulce G Romero-Urbina
M Josefina Arellano-Jiménez
Humberto H Lara
Christopher Pierce
Miguel Jose-Yacaman
Journal: Journal of nanobiotechnology (2015)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Candida albicans; biofilm formation; silver nanoparticles; antifungal strategies; cell wall disruption
Affiliations: Department of Physics and Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, 78249, USA. ., Department of Biology and South Texas Center for Emerging Infectious Diseases, The University of Texas at San Antonio, San Antonio, TX, 78249, USA. .

Abstract:  Background: Candida albicans is the most common pathogenic fungus isolated in bloodstream infections in hospitalized patients, and candidiasis represents the fourth most common infection in United States hospitals, mostly due to the increasing numbers of immune- and medically-compromised patients. C. albicans has the ability to form biofilms and morphogenetic conversions between yeast and hyphal morphologies contribute to biofilm development and represent an essential virulence factor. Moreover, these attached communities of cells are surrounded by a protective exopolymeric matrix that effectively shelters Candida against the action of antifungals. Because of dismal outcomes, novel antifungal strategies, and in particular those targeting biofilms are urgently required. As fungi are eukaryotic, research and development of new antifungal agents has been difficult due to the limited number of selective targets, also leading to toxicity. Results: By microwave-assisted techniques we obtained pure 1 nm spherical silver nanoparticles ideal for their potential biological applications without adding contaminants. A phenotypic assay of C. albicans demonstrated a potent dose-dependent inhibitory effect of silver nanoparticles on biofilm formation, with an IC50 of 0.089 ppm. Also silver nanoparticles demonstrated efficacy when tested against pre-formed C. albicans biofilms resulting in an IC50 of 0.48 ppm. The cytotoxicity assay resulted in a CC50 of 7.03 ppm. The ultrastructural differences visualized under SEM with silver nanoparticles treatment were changes in the surface appearance of the yeast from smooth to rough thus indicating outer cell wall damage. On the fungal pre-formed biofilm true hyphae was mostly absent, as filamentation was inhibited. TEM measurement of the cell-wall width of C. albicans after treatment resulted in significant enlargement (206 ± 11 nm) demonstrating membrane permeabilization. Conclusions: Our results demonstrate that silver nanoparticles are potent inhibitors of C. albicans biofilm formation. SEM observations are consistent with an overall loss of structure of biofilms mostly due to disruption of the outer cell membrane/wall and inhibition of filamentation.TEM indicates the permeabilization of the cell wall and subsequent disruption of the structural layers of the outer fungal cell wall. The anti-biofilm effects are via cell wall disruption. 

Retracted: No

PubPeer comments:
 Thank you for your amazing article. I found an error in figure 9. In fig. 9, the authors wrote a,b images show yeast without treatment. Then Treated yeast with Ag-NPs are shown in (b) and (d). How this b untreated and b treated. I think is a typo error and b must be replaced by c and rearrangement of the image field to be a b c d due to letters were distributed incorrectly. For instance, a and b represented untreated C. albicans with CW diameter of 0.12 um and 0.07 um however c represented treated fungal cells with Ag-NPs showing enlargement in CW width (0.37 um) while d represented the affinity between Ag-NPs and cell walls as well as demonstrated the potentiality of NPs to form pores or holes in CW. I understood this due to I read the whole paper, however, the person who looks only in figure legend, he she will be confused due to the error. Another point, in material and methods, a section of characterization of NPs. The authors wrote u2018u2019zeta potential measurement of nanoparticles was determined by dynamic light scatteringu2019u2019. This is difficult to understand due to DLS is analysis for the estimation hydrodynamic diameter of NPs in liquid while Zeta potential is another analysis describing the charge of NPs surface and measured by Zetasizer instrument. I attached a link to support my writing. https: www.researchgate.net post Can_someone_explain_the_difference_between_dynamic_light_scattering_and_zeta_potential_Is_DLS_used_to_measure_zeta_potential_or_are_they_different ,