Mitigation of acyl-homoserine lactone (AHL) based bacterial quorum sensing, virulence functions, and biofilm formation by yttrium oxide core/shell nanospheres: Novel approach to combat drug resistance

Abstract

The present study evaluated the efficacy of Y₂O₃:Tb (core) and Y₂O₃:Tb@SiO₂ nanospheres (core/shell NSs) against virulence functions regulated by quorum sensing (QS) and biofilm formation in pathogenic bacteria. Scanning electron microscope (SEM) images were used to study the size, shape, and morphology. The images clearly displayed spherical shaped, mono-dispersed particles with narrow size distribution and an average grain size of 110-130 nm. The chemical composition of the samples was determined by using energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). We determined the impact of core and core/shell NSs on QS using sensor strains of Chromobacterium violaceum CVO26 and Pseudomonas aeruginosa PAO1 in a comparative study. Sub-MICs of core and core/shell NSs substantially suppressed QS-controlled violacein production in C. violaceum. Similar concentration-dependent effect of sub-MICs of synthesized core and core/shell NSs was observed in the QS-regulated virulence functions (elastase, total protease, pyocyanin production, swarming motility, and exopolysaccharide production) in PAO1. A concentration-dependent decrease (14-60%) was recorded in the biofilm forming capability of PAO1, upon treatment with core and core/shell NSs. Moreover, core/shell NSs were more effective in inhibiting biofilm at higher tested concentrations as compared to core-NSs. The synthesized NSs demonstrated significantly impaired attachment of cells to the microtiter plate indicating that NSs target biofilm inhibition at the attachment stage. Based on these results, we predict that core and core/shell NSs may be an alternative to combat the threat of drug-resistant pathogenic bacteria.

Figure 1

(a) Low magnification SEM image (b,c) high magnification SEM image and (d) EDX analysis of core/shell NSs.

Figure 2

XPS analysis (a)Y (3d_5/2) (b) O(1 s) (c) Tb (4d_5/2) and (d) Si (2p_3/2) signals of core/shell NSs.

Figure 3

Assay for QS inhibition. (a) Inhibition of violacein production in CVO26 by core and core/shell NSs concentrations (25, 50, 100, and 200 μg/mL) was quantified spectrophotmetrically (OD at 585 nm). (b) Growth curve analysis of CVO26 at 200 µg/mL concentration of NSs.

Figure 4

Effect on QS regulated virulence traits of PAO1. (a) Growth curve analysis of PAO1 at 200 µg/mL concentration of NSs. (b) Effect of sub-MICs of TYO on inhibition of quorum sensing regulated virulence factors. (c) Effect of sub-MICs of TYSO on inhibition of quorum sensing regulated virulence factors. Data is presented as mean percent reduction ± SD. ^*Significance at p ≤ 0.05, ^**significance at p ≤ 0.005, ^***Significance at p ≤ 0.001.

Figure 5

Anti-biofilm activity of NSs. (a) Percent inhibition of biofilm formation of PAO1 by sub-MICs of core and core/shell NSs using microtitre plate assay. (b) Images of (a–c) CV-staining light microscope, (d–f) acridine orange staining CLSM. (a,d) untreated control; (b,e) 200 µg/mL core and (c,f) 200 µg/mL core/shell NSs.

Figure 6

The effect of sub-MICs of synthesized core and core/shell NSs on the attachment of PAO1, expressed as percentage inhibition.