Effect of silver nanoparticles on Candida albicans biofilms: an ultrastructural study

Abstract

BackgroundCandida 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.ResultsBy 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.ConclusionsOur 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0147-8) contains supplementary material, which is available to authorized users.

Antimicrobial properties of acrylic resins for dentures impregnated with silver nanoparticles

“…Dobijeni rezultati nisu dokazali fungicidni efekat AgNPs. Literaturno dostupni podaci jasno opisuju dejstvo AgNPs na kolonije kandide u ustima pacijenta, što uslovljava ponavljanje istraživanja istim metodološkim postupkom, kao i uvođenjem novih metoda 23,24 . S obzirom na ograničenost ovog istraživanja ne možemo doneti jasne sudove o antimikrobnim svojstvima impregniranih akrilatnih materijala.…”

“…The results did not prove the fungicidal effect of AgNPs. Literary available data clearly describe the effect AgNPs on the colonization of Candida in the mouth, dictating the necessity for the repetition of the same methodological research process, as well as the introduction of new research methods 23,24 . Given the limitations of this study, we cannot make a clear judgment on the antimicrobial properties of resin impregnated materials.…”

Inhibition of Candida albicans biofilm by pure selenium nanoparticles synthesized by pulsed laser ablation in liquids

“…These are ideal conditions for C. albicans to grow as budding yeast. Biofilms are quantified using well established phenotypic assay previously reported by our group (23). Briefly, after cells are harvested from overnight YPD broth cultures they were washed and grown in RPMI-1640 (Corning-Cellgro), with biofilms formed on sterile flat-bottom microtiter plate (Costar, Corning Inc. USA) following incubation for 24 h. The biofilm and sessile cells strongly attached to the flat-bottom wells were gently washed twice with sterile phosphate-buffered saline (PBS) to ensure removal of non-adherent yeast cells, and the amount of biofilm inhibition quantified using a colorimetric assay based on the reduction of a tetrazolium salt, the XTT reduction assay (Sigma Chemical Co., St. Louis, Mo.…”

“…For those reasons, it is extremely urgent to develop new drugs to fight those infections. The solution may come from nanotechnology where nanoparticles being less than one hundred nanometers in size are especially adapted to interact with bacteria(22) and fungus(23) due to their large surface to volume ratio. Therefore, there is a specific interest in synthesizing pure Se NPs for nano-medical applications(24, 25).…”

Synergistic action of amphotericin B and rhamnolipid in combination on Candida parapsilosis and Trichosporon cutaneum

“…Pires et al (2011) also studied the combined influence of cinnamon oil and amphotericin B on Candida biofilms; however, the interaction was indifferent (FICi 1.5). It is also known to be possible to inhibit preformed biofilm by silver nanoparticles (diameter 2 nm) as reported by (Lara et al 2015). Ziccardi et al (2015) investigated the susceptibility of Candida biofilms to antifungal drugs (amphotericin B, itraconazole, fluconazole, caspofungin and variconazole), but they failed to find the MIC values for biofilm (in the range of observed concentrations).…”