Background:The extensive application of silver compounds especially in nanomedicine, has increased the need to develop environmental friendly and cost effective route to synthesizing silver nanoparticles (AgNPs). Methods:Water, diethyl ether, and ethanol were used in the extraction of Waltheria americana root. Silver nanoparticles (AgNPs) were synthesized by reacting 0.001 M AgNO3 solution with the different crude extracts of W. americana root in the ratio of 10:1. The synthesized AgNPs were analyzed using UV-visible spectrophotometer, X-ray diffraction (XRD), scanning electron microscope (SEM), and FTIR techniques. The different crude extracts and their synthesized colloidal AgNPs were tested against Proteus species, Streptococcus species, Klebsiella species, Staphylococcus aureus, and ciprofloxacin (control). Results:UV-vis results showed surface plasmon resonance (SPR) at 415, 435, and 425 nm for synthesized colloidal AgNPs from water, diethyl ether, and ethanol extracts, respectively. When screened against all test organisms, the synthesized colloidal AgNPs from diethyl ether extract of W. americana root (WARDEEP) showed more improved antimicrobial efficacy than other crude extracts and their synthesized AgNPs. The strongest antimicrobial activity of WARDEEP against all test organisms were at 400, 100, and 200 mg/mL concentrations for Proteus species and Staphylococcus aureus, Klebsiella species, and Streptococcus species, respectively. From minimum inhibitory concentration (MIC) results, it was observed that WARDEEP exhibited a strong antibiotic activity against Proteus and Streptococcus species at a least value of 12.5 mg/ mL concentration. Minimum bactericidal concentration (MBC) results showed that WARDEEP exhibited a minimum antibiotic activity at 25 mg/mL concentration against Proteus and Streptococcus species. Conclusions:Therefore, silver nanoparticles were sucessfully synthesized from all the crude extracts. The synthesized silver nanoparticles could comparatively provide better alternative treatment to both gram-positive and gram-negative bacteria than the crude plant extracts.
