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

Abstract

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 AgNO3 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 (Staphylococcus aureus ATCC 6538, clinical Enterococcus faecalis, and S. aureus) and two Gram-negative bacteria (two clinical Escherichia coli) 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 E. coli and S. aureus 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 AgNO3. The antibacterial activity of the two extracts was dose-dependent, and the largest inhibition diameter was observed for the Gram-positive bacteria (S. aureus 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 (S. aureus ATCC 6538) to 12.5 (E. coli 1 and E. coli 2), whereas the MICs of the EEs varied from 1.5625 (S. aureus 1, S. aureus ATCC 6538, and E. faecalis) to 6.25 (E. coli 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 (S. aureus ATCC 6538) to 50 (S. aureus 1), whereas those of the EEs varied from 6.25 (S. aureus 1) to 25 (E. coli 1 and E. faecalis). Ethanolic grapefruit extracts demonstrated an ability to modulate cefazolin on E. coli and S. aureus but were completely indifferent to ampicillin on E. coli. 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.

Assessment of antimicrobial activity of ethanolic and aqueous extracts ofAesculus hippocastanumL. (horse chestnut) bark against bacteria isolated from urine of patients diagnosed positive to urinary tract infections

“…This residue cloudiness could therefore explain the higher mass yield in AE (24,3%) compared to EE (13,4%). Several authors [17,18,24,25] reported observations similar to our findings while others [26,27] found opposite results. Therefore, as…”

“…The well diffusion method previously described [18] was used to assess the antimicrobial activity of the extracts. Briefly, 15 ml of sterile Muller Hinton Agar (for bacteria) was poured into petri dishes and 100 μl of each microorganism were spread.…”

“…Ethanolic solution (80%, v/v) and distilled water was used because they have been reported to be an efficient solvent for the extraction of bioactive compounds in the medicinal plants used in this study. As we described in our previous investigation [18] fifty grams (30g) of vegetal material was weighed and added to 270 ml of the solvent in separate conical flasks. The flasks were covered tightly and were shaken at 200 rpm for 24h and 25°C in a shaker incubator (Heidolph Inkubator 1000 coupled with Heidolph Unimax 1010, Germany).…”

“…Indeed, several recent studies have reported a considerable increase in antibiotic resistance in uropathogens and an unprecedented number of multidrug-resistant germs worldwide [10,11]. To respond to this dangerously worrying situation, research teams from all over the world are permanently evaluating the use of potential alternatives to antibiotics such as nanoparticles [12], probiotics [13,14], phage therapy [15], antimicrobial peptides [16] and medicinal plants [17,18]. Among these alternatives, medicinal plants appear as the most credible [19] since it is well known that plants have been used for millennia in the treatment and prevention of various diseases, including bacterial infections and some of these herbal remedies have been shown to be effective in preventing and treating UTIs [19].…”

Prolonged Exposure to Antimicrobials Induces Changes in Susceptibility to Antibiotics, Biofilm Formation and Pathogenicity in Staphylococcus aureus

“…These infections are more serious due to the growth of antibiotic resistance worldwide. Recent estimates have shown that antibiotic resistance is responsible for 700,000 annual deaths worldwide, 230,000 of which have resulted from multidrug-resistant tuberculosis [2,3]. The World Health Organization estimates that if nothing is done to address this problem, drug-resistant diseases may cause 10 million deaths each year by 2050 and damage to the economy as catastrophic as the 2008-2009 global financial crisis [2].…”