Use of Nanoparticles to Prevent Resistance to Antibiotics—Synthesis and Characterization of Gold Nanosystems Based on Tetracycline

Abstract

Antimicrobial resistance (AMR) is a serious public health problem worldwide which, according to the World Health Organization (WHO), requires research into new and more effective drugs. In this work, both gold nanoparticles covered with 16-3-16 cationic gemini surfactant (Au@16-3-16) and DNA/tetracycline (DNA/TC) intercalated complexes were prepared to effectively transport tetracycline (TC). Synthesis of the Au@16-3-16 precursor was carried out by using trihydrated gold, adding sodium borohydride as a reducing agent and the gemini surfactant 16-3-16 as stabilizing agent. Circular dichroism and atomic force microscopy techniques were then used to ascertain the optimal R range of the relationship between the concentrations of Au@16-3-16 and the DNA/TC complex (R = CAu@16-3-16/CDNA) that allow the obtainment of stable and compact nanosystems, these characteristics being fundamental for their use as antibiotic transporters. Stability studies over time were carried out for distinct selected Au@16-3-16 and Au@16-3-16/DNA-TC nanoformulations using the ultraviolet–visible spectrophotometry technique, checking their stability for at least one month. In addition, in order to know the charge and size distribution of the nanocomplexes, DLS and zeta potential measurements were performed in the solution. The results showed that the characterized nanosystems were highly charged, stable and of a reduced size (<100 nm) that allows them to cross bacterial membranes effectively (>1 μm). Once the different physicochemical characteristics of the gold nanosystems were measured, Au@16-3-16 and Au@16-3-16/DNA-TC were tested on Escherichia coli and Staphylococcus aureus to study their antibacterial properties and internalization capacity in microbes. Differences in the interaction of the precursors and the compacted nanosystems generated were observed in Gram-positive and Gram-negative bacteria, possibly due to membrane damage or electrostatic interaction with internalization by endocytosis. In the internalization experiments, depending on the treatment application time, the greatest bacterial destruction was observed for all nanoformulations explored at 18 h of incubation. Importantly, the results obtained demonstrate that both new nanosystems based on TC and Au@16-3-16 precursors have optimal antimicrobial properties and would be beneficial for use in patients, avoiding possible side effects.

Synergistic Antibacterial Effects of Amoxicillin and Gold Nanoparticles: A Therapeutic Option to Combat Antibiotic Resistance

“…It is important to note that the NS 2 preparation has the same AMOX concentration as the control in Figure 13B; thus, the results obtained here support the benefit of using Au@16-mph-16 nanoparticles as nanocarriers for antibacterial drugs. Being a Gram-positive bacterium, the destabilization mechanisms of the biosynthetic machinery via the induction of the release of free oxygen radicals are similar to those previously described for S. aureus [21,[70][71][72][73][74][75][76][77]. However, these bacteria are not reactive to catalase, while S. aureus are positive.…”

“…In Figure 12E,F, we can see the effect of the treatment with the nanosystem. Since the NS 2 charge is negative, the mechanism of action is driven by an electrostatic interaction, contributing to internalization by endocytosis, releasing the antibiotic from the precursor and causing a mismatch in metabolic signal transduction similar to that described above, thereby destroying the biosynthetic machinery of the microorganism and causing its death [21,[70][71][72][73][74][75][76][77]. Finally, in Figure 13, we can see the result of the treatments carried out on S. pneumoniae, which is a lactic acid, facultative anaerobic, catalase-negative bacterium.…”

“…As is already known, the use of nanocomplexes that include an antibiotic in their structure is an effective and efficient strategy to combat resistance to antimicrobials, while also minimizing side effects [ 21 , 49 ]. In this work, we used Au@16-mph-16/DNA-AMOX nanocomplexes to efficiently transport AMOX to the interior of the target.…”

“…Visualization of the samples was performed with a Zeiss Libra microscope. For more details, see the protocol followed by the research group in previous works [ 21 , 40 , 44 , 45 , 46 ]. The different samples were studied by observation of between 500 to 700 bacteria per experiment.…”

“…The mechanisms of intracellular antibiotic reduction may be due to a mechanism based on efflux pumps that expel the antibiotic [ 19 ], or a mechanism that modifies the external bacterial membrane, so that the bacteria lose or modify porins, thereby preventing the entry of the antibiotic. An example of these are beta-lactams, hydrophilic antibiotics that cross porins [ 20 ], or the use of vehicles made up of gold nanoparticles (AuNPs) that can interact with the exterior of the microorganism, destabilizing its exterior [ 21 ].…”