Antimicrobial activity of biogenically produced spherical Se-nanomaterials embedded in organic material against Pseudomonas aeruginosa and Staphylococcus aureus strains on hydroxyapatite-coated surfaces

Abstract

In an effort to prevent the formation of pathogenic biofilms on hydroxyapatite (HA)-based clinical devices and surfaces, we present a study evaluating the antimicrobial efficacy of Spherical biogenic Se-Nanostructures Embedded in Organic material (Bio Se-NEMO-S) produced by Bacillus mycoides SelTE01 in comparison with two different chemical selenium nanoparticle (SeNP) classes. These nanomaterials have been studied as potential antimicrobials for eradication of established HA-grown biofilms, for preventing biofilm formation on HA-coated surfaces and for inhibition of planktonic cell growth of Pseudomonas aeruginosa NCTC 12934 and Staphylococcus aureus ATCC 25923. Bio Se-NEMO resulted more efficacious than those chemically produced in all tested scenarios. Bio Se-NEMO produced by B. mycoides SelTE01 after 6 or 24 h of Na₂ SeO₃ exposure show the same effective antibiofilm activity towards both P. aeruginosa and S. aureus strains at 0.078 mg ml^-1 (Bio Se-NEMO₆ ) and 0.3125 mg ml^-1 (Bio Se-NEMO₂₄ ). Meanwhile, chemically synthesized SeNPs at the highest tested concentration (2.5 mg ml^-1 ) have moderate antimicrobial activity. The confocal laser scanning micrographs demonstrate that the majority of the P. aeruginosa and S. aureus cells exposed to biogenic SeNPs within the biofilm are killed or eradicated. Bio Se-NEMO therefore displayed good antimicrobial activity towards HA-grown biofilms and planktonic cells, becoming possible candidates as new antimicrobials.

Figure 1

Dynamic light scattering (DLS) analysis of biogenic SeNPs produced by Bacillus mycoides SelTE01 after 6 (A) or 24 h (B) of Na₂SeO₃ exposure, and chemical SeNPs made using L‐cysteine (C) or ascorbic Acid (D).

Figure 2

Transmission Electron Microscopy (TEM) analysis of biogenic SeNPs produced by Bacillus mycoides SelTE01 after 6 (A) or 24 h (B) of Na₂SeO₃ exposure, and chemical SeNPs made using L‐cysteine (C) or ascorbic Acid (D).

Figure 3

Energy‐dispersive X‐ray spectroscopy (EDX) spectra of Bio Se‐NEMO‐S produced by Bacillus mycoides SelTE01 after 6 (A) or 24 h (B) of Na₂SeO₃ exposure, and chemical SeNPs made using L‐cysteine (C) or ascorbic Acid (D).

Figure 4

Zeta potential measurements of Bio Se‐NEMO‐S produced by Bacillus mycoides SelTE01 after 6 (A) or 24 h (B) of Na₂SeO₃ exposure, and chemical SeNPs made using L‐cysteine (C) or ascorbic acid (D).

Figure 5

Minimal Biofilm Eradication Concentration (MBEC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) established biofilms for 24 h, and subsequently exposed for 24 h to Bio Se‐NEMO‐S₆ and Bio Se‐NEMO‐S₂₄. Error bars show the standard deviation.

Figure 6

Minimal Biofilm Eradication Concentration (MBEC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) established biofilms for 24 h, and subsequently exposed for 24 h to L‐cys SeNPs and Asc SeNPs. Error bars show the standard deviation.

Figure 7

Minimal Biofilm Prevention Concentration (MBPC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) growing biofilms exposed for 24 h to Bio Se‐NEMO‐S₆ and Bio Se‐NEMO‐S₂₄. Error bars show the standard deviation.

Figure 8

Minimal Biofilm Prevention Concentration (MBPC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) growing biofilms exposed for 24 h to L‐cys SeNPs and Asc SeNPs. Error bars show the standard deviation.

Figure 9

Minimal Inhibition Concentration (MIC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) growing planktonic cells exposed for 24 h to Bio Se‐NEMO‐S₆ and Bio Se‐NEMO‐S₂₄. Error bars show the standard deviation.

Figure 10

Minimal Inhibition Concentration (MIC) assays of Pseudomonas aeruginosa NCTC 12934 (A) and Staphylococcus aureus ACTT 25923 (B) growing planktonic cells exposed for 24 h to L‐cys SeNPs and Asc SeNPs. Error bars show the standard deviation.

Figure 11

Confocal Laser Scanning Microscopy (CLSM) of HA‐coated peg (A), Pseudomonas aeruginosa biofilm grown onto HA‐coated peg (B) and in the presence of bio6 SeNPs at the concentration of 0.039 mg ml⁻¹ (C), 0.078 mg ml⁻¹ (MBBC) (D), 1.25 mg ml⁻¹ (E), or in the presence of L‐cys SeNPs at the concentration of 0.625 mg ml⁻¹ (F), 1.25 mg ml⁻¹ (G), 2.5 mg ml⁻¹ (H).

Figure 12

Confocal Laser Scanning Microscopy (CLSM) of HA‐coated peg (A), Staphylococcus aureus biofilm grown onto HA‐coated peg (B) and in the presence of bio6 SeNPs at the concentration of 0.039 mg ml⁻¹ (C), 0.078 mg ml⁻¹ (MBBC) (D), 1.25 mg ml⁻¹ (E), or in the presence of L‐cys SeNPs at the concentration of 0.625 mg ml⁻¹ (F), 1.25 mg ml⁻¹ (G), 2.5 mg ml⁻¹ (H).