Abstract
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.
Highlights
Opportunistic bacteria like Escherichia coli, Micrococcus sp., Staphylococcus sp., and others have been demonstrated to form rigid biofilms, a community of microbial cells adherent to a substrate and embedded in a polysaccharide matrix (EPS) produced by cells themselves [1]
Using the drop plate method and the differential fluorescent microscopy to estimate the viability of bacteria, we show explicitly that, in contrast to ciprofloxacin, the quaternary ammonium salt of pyridoxine (N,N-dimethyl-N-((2,2,8-trimethyl-4H-[1, 3]dioxino[4,5c]pyridin-5-yl)methyl)octadecan-1-aminium chloride) completely kills the biofilm-embedded S. aureus and S. epidermidis cells at concentrations of 64 and 16 μg/mL, respectively
In our previous works we have reported the synthesis of quaternary ammonium and phosphonium salts of pyridoxine and 6hydroxymethylpyridoxine which had demonstrated activity against S. aureus and S. epidermidis [24,25,26]
Summary
Opportunistic bacteria like Escherichia coli, Micrococcus sp., Staphylococcus sp., and others have been demonstrated to form rigid biofilms, a community of microbial cells adherent to a substrate and embedded in a polysaccharide matrix (EPS) produced by cells themselves [1]. Bacteria are extremely resistant to biocides, antibiotics and to the human immune system [1, 2]. This leads to the drastic increase in the bacterial resistance against antimicrobial treatment, higher frequency of nosocomial infections, and creating difficulties in the microbiological diagnostics of infectious diseases [2, 3]. The biofilm formation could be blocked by either natural agents like
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