Abstract
Enhancing the antibacterial activity of old antibiotics by a multitarget approach, such as combining antibiotics with metal nanoparticles, is a valuable strategy to overcome antibacterial resistance. In this work, the synergistic antimicrobial effect of silver nanoparticles and antibiotics, immobilized on a solid support, was investigated. Nanometric layered double hydroxides (LDH) based on Zn(II) and Al(III) were prepared by the double microemulsion technique. The dual function of LDH as an anionic exchanger and support for metal nanoparticles was exploited to immobilize both silver and antibiotics. Cefazolin (CFZ), a β-lactam, and nalidixic acid (NAL), a quinolone, were selected and intercalated into LDH obtaining ZnAl-CFZ and ZnAl-NAL samples. These samples were used for the growth of silver nanoparticles with dimension ranging from 2.5 to 8 nm. Silver and antibiotics release profiles, from LDH loaded with antibiotics and Ag/antibiotics, were evaluated in two different media: water and phosphate buffer. Interestingly, the release profiles are affected by both the acceptor media and the presence of silver. The synergistic antibacterial activity of LDH containing both silver and antibiotics were investigated on gram-positives (Staphylococcus aureus and Streptococcus pneumoniae) and gram-negatives (Pseudomonas aeruginosa) and compared with the plain antimicrobials and LDH containing only antibiotics or silver.
Highlights
After they were discovered, it was clear that antibiotics would have become a mixed blessing
Given the conditions of synthesis, in which the surfactant bromide counterions are diffused in the micellar water pool, the resulting layered double hydroxides (LDH) will be preferentially in bromide form (ZnAl-Br)
Other observations should regard the nature of the target bacteria and the mechanisms employed by the microorganism to develop resistance; despite all these specific evaluations, this study demonstrates that silver has a potential synergistic effect when placed in combination with other species to target a broad spectrum of both gram-positive and gram-negative bacteria
Summary
After they were discovered, it was clear that antibiotics would have become a mixed blessing. The escalating crisis of antibiotic resistance is pressing science to take action in order to stave off a tremendous decline towards a post-antibiotic era [3] This quest includes the diffusion of new drugs [4,5], the repurpose of older ones [6], the administration of mixed antibiotic regimens [7,8], and the testing of target-based approaches focused on the development of specific inhibitors [9,10]. Another strategy involves the combination of antibiotics with metal nanoparticles (NPs)
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