A XANES study of the antibacterial activity of silver ions against Acinetobacter baumannii

Abstract

One of the most challenging antimicrobial-resistant Gram-negative bacilli to manage and cure is pathogenic Acinetobacter baumannii. Numerous bacterial species, including the tough A. baumannii, are strongly inhibited by silver ions. However, there is currently a scarcity of information regarding the mechanism of silver ions' bactericidal effect. The objective of this research was to use X-ray near-edge structure (XANES) spectroscopy to investigate the antibacterial activity of silver ions against A. baumannii. The local environment around silver ions and their bonding to specific spots in the biomass can be studied using this non-destructive technique. The obtained results demonstrated that the biomass sample of A. baumannii treated with silver included formation of silver bonding to -SH, -NH, and -OH groups, with Ag-N and Ag-O being the most dominant binding types. The presence of uniformly distributed silver at the bacterial cells as revealed by scanning electron microscopy (SEM) suggests that the majority of the silver ions bond to the outer cell membrane of A. baumannii. Accordingly, the antibacterial mechanism most likely involves silver ions connecting to locations in A. baumannii's outer cell membrane as well as to the amino acids.