Antibacterial activity of grapefruit peel extracts and green-synthesized silver nanoparticles.

BACKGROUND AND AIM

The gradual loss of efficacy of conventional antibiotics is a global issue. Plant material extracts and green-synthesized nanoparticles are among the most promising options to address this problem. Therefore, the aim of this study was to assess the antibacterial properties of aqueous and hydroalcoholic extracts of grapefruit peels as well as their inclusion in green-synthesized silver nanoparticles (AgNPs).

MATERIALS AND METHODS

Aqueous and hydroalcoholic extracts (80% v/v) were prepared, and the volume and mass yields were determined. The synthesis of AgNPs was done in an eco-friendly manner using AgNO as a precursor. The nanoparticles were characterized by ultraviolet-vis spectrometry and photon cross-correlation spectroscopy. The antibacterial activity of the extracts was tested on three Gram-positive bacteria ( ATCC 6538, clinical , and ) and two Gram-negative bacteria (two clinical ) using various concentrations of extracts (100, 50, 25, 12, and 5 mg/mL and 5% dimethyl sulfoxide as negative control). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using the microdilution method. Modulation of cefazoline and ampicillin on resistant and strains was added to the mixture design response surface methodology with extreme vertices design, with the diameters of inhibition and the fractional inhibitory concentration index as responses and factors, respectively. The antibiotic, the ethanolic extract, and water varied from 0.1 MIC to 0.9 MIC for the first two and from 0 to 0.8 in proportion for the third. Validating the models was done by calculating the absolute average deviation, bias factor, and accuracy factor.

RESULTS

The volume yield of the EE and aqueous extract (AE) was 96.2% and 93.8% (v/v), respectively, whereas their mass yields were 7.84% and 9.41% (m/m), respectively. The synthesized AgNPs were very uniform and homogeneous, and their size was dependent on the concentration of AgNO. The antibacterial activity of the two extracts was dose-dependent, and the largest inhibition diameter was observed for the Gram-positive bacteria ( ATCC 6538; AE, 12; EE, 16), whereas AgNPs had a greater effect on Gram-negative bacteria. The MICs (mg/mL) of the AEs varied from 3.125 ( ATCC 6538) to 12.5 ( and 2), whereas the MICs of the EEs varied from 1.5625 ( 1, ATCC 6538, and ) to 6.25 ( 1). There was a significant difference between the MICs of AEs and EEs (p=0.014). The MBCs (mg/mL) of the AEs varied from 12.5 ( ATCC 6538) to 50 ( 1), whereas those of the EEs varied from 6.25 ( 1) to 25 ( 1 and ). Ethanolic grapefruit extracts demonstrated an ability to modulate cefazolin on and but were completely indifferent to ampicillin on .

CONCLUSION

Grapefruit peel extracts and their AgNPs exhibit antibacterial properties that can be exploited for the synthesis of new antimicrobials and their EEs may be efficiently used synergistically with other antibiotics against bacteria with intermediate susceptibility.