Comparative Antimicrobial Potential of Green Synthesized Sliver-nano-particles Using Three Different Natural Gums on Potentially Pathogenic Microbes from Veterinary Clinical Cases and Associated Environment

Abstract

Metallic silver, its compounds and nano-particles (SNPs) are known for their wide-spectrum antimicrobial potential. However, little is understood about the best material for the green synthesis of SNPs. This study was conducted to find out the best of the three natural gums viz., piyar or chironji (Buchanania lanzan) gum, gum acacia (Acacia nilotica) and jhingan (Lannea coromandelica) gum used for green synthesis of SNPs and to evaluate the effect of aspirin, flunixin meglumine and pacetamol on in vitro antimicrobial activity of SNPs. The study was conducted on 376 Gram-negative (G-ve), 184 Gram-positive (G+ve) bacteria and 7 yeasts and moulds, belonging to 41 genera. The test strains were from clinical cases (392), environmental sources (120) and, reference culture (55) repositories. The MIC of silver-nano-particles for 567 isolates of bacteria and yeast and moulds was 1.6 ± 2.03, 2.13 ± 2.57, 1.46 ± 1.87, and 1.35 ± 1.85 µg of silver mL -1 in MHB when the source of silver in the medium was PGNP, AGNP, JGNP and silver nitrate, respectively. Strains of different origins had a wide difference in MIC of silver, 10 of the 12 strains having MIC of silver >4 µg mL -1 were detected from herbivores and one each was from a dog and a fish. Of the three SNPs, SNPs synthesized using gum acacia (AGNP) had the least antimicrobial activity (p < 0.01) while SNPs synthesized using jhingan gum (JGNPs) were the most effective among all the three SNPs. Significantly (p ≤ 0.05) larger number of G-ve bacteria were resistant to SNPs than G+ve bacteria if susceptibility limit was set at 0.25 or 0.5 µg mL -1 but no such difference was evident at 1 or 2 µg mL -1 concentration of silver. Among strains of 17 different genera compared, R. terrigena isolates were significantly (p < 0.05) more often resistant than isolates of most of the other bacteria (Acinetobacter,