Opportunistic bacteria Staphylococcus aureus and Staphylococcus epidermidis often form rigid biofilms on tissues and inorganic surfaces. In the biofilm bacterial cells are embedded in a self-produced polysaccharide matrix and thereby are inaccessible to biocides, antibiotics, or host immune system. Here we show the antibacterial activity of newly synthesized cationic biocides, the quaternary ammonium, and bisphosphonium salts of pyridoxine (vitamin B6) against biofilm-embedded Staphylococci. The derivatives of 6-hydroxymethylpyridoxine were ineffective against biofilm-embedded S. aureus and S. epidermidis at concentrations up to 64 μg/mL, although all compounds tested exhibited low MICs (2 μg/mL) against planktonic cells. In contrast, the quaternary ammonium salt of pyridoxine (N,N-dimethyl-N-((2,2,8-trimethyl-4H-[1,3]dioxino[4,5-c]pyridin-5-yl)methyl)octadecan-1-aminium chloride (3)) demonstrated high biocidal activity against both planktonic and biofilm-embedded bacteria. Thus, the complete death of biofilm-embedded S. aureus and S. epidermidis cells was obtained at concentrations of 64 and 16 μg/mL, respectively. We suggest that the quaternary ammonium salts of pyridoxine are perspective to design new synthetic antibiotics and disinfectants for external application against biofilm-embedded cells.
The composite silver and gold nanoparticles (AgNPs and AuNPs) coated with nonionic amphiphilic block copolymers (Pluronics L121, F68, or F127) are prepared by their adsorption under critical micelle concentrations. It is found that Pluronics bind to the surface of metal NPs as a very thin film by the hydrophobic association through poly(propylene oxide) block of the copolymers. The modification increases the colloidal stability of NPs with increasing hydrophilic-lipophilic balance of Pluronics in the order of L121, F127, and F68. In order to investigate the potentials of polymer coated noble metal NPs as surface-enhanced Raman spectroscopy (SERS) probes, fluorescent dyes and doxorubicin are used as model compounds. It is found that Pluronic component promotes the adsorption of these compounds on the composite NPs resulting in a considerable increase of Raman signal. This effect is attributed to increased concentration of the analyte molecules on the composite surface due to the hydrophobic and charge-charge interactions between the analytes and the Pluronic coat, and the stabilization of NPs by poly(ethylene oxide) blocks. The copolymer coated AgNPs show higher SERS activity than the counterparts prepared with AuNPs. Among the prepared composites, the AgNPs modified with Pluronic F127 containing extended poly(propylene oxide) and poly(ethylene oxide) blocks exhibit maximal Raman activity using rhodamine 6G (Rh6G) with a EF of 9.04 x 10(6). The results show that the developed Pluronic-based SERS probes can be used for sensitive and selective analysis of organic analytes.
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