Studies by various researchers have established citrate stabilized AgNPs as an effective bactericidal nanomaterial. El-Kheshen and El-Rab reported a MIC of 125 mg ml for the citrate capped AgNPs against E. coli ATCC 8739 strain for an
initial bacterial concentration of 105 to 106 CFU ml. The AgNPs were found to be polydispersed in nature with a size
range of 20 to 65 nm. In addition to spherical nanoparticles, rods, triangles, and irregular shapes were also reported. Thus, their antibacterial activity can not solely be explained on the basis of size, since the shape of the silver nanoparticles may have a significant effect.14 A AgNP colloidal suspension (size, not reported) has also been used by Taner et al.40 for antibacterial purposes with a reported MIC of >150 mg ml against E. coli DH5a strain at 108 CFU ml initial bacterial concentration. Citrate stabilized AgNPs of varying size, i.e., 120 nm and 160 nm exhibited variations in MIC and MBC values against multi-drug resistant bacterial strains isolated from hospital wastes for studies performed at 103 to 104 CFU ml initial bacterial concentration. For Staphylococcus aureus and Bacillus megaterium, the MIC/MBC values for these AgNPs were found to be 60/160 mg ml and 80/160 mg ml, respectively.