Abstract
Biofilm-forming bacteria present formidable challenges across diverse settings, and there is a need for new antimicrobial agents that are both environmentally acceptable and relatively potent against microorganisms in the biofilm state. The antimicrobial activity of three naturally occurring, low molecular weight, phenols, and their derivatives were evaluated against planktonic and biofilm Staphylococcus epidermidis and Pseudomonas aeruginosa. The structure activity relationships of eugenol, thymol, carvacrol, and their corresponding 2- and 4-allyl, 2-methallyl, and 2- and 4-n-propyl derivatives were evaluated. Allyl derivatives showed a consistent increased potency with both killing and inhibiting planktonic cells but they exhibited a decrease in potency against biofilms. This result underscores the importance of using biofilm assays to develop structure-activity relationships when the end target is biofilm.
Highlights
Pseudomonas aeruginosa is a Gram-negative, rod shaped bacterium with a pronounced tendency to form biofilms
After coupons were removed from the Center for Disease Control (CDC) reactor they were rinsed and transferred to separate, 50 mL conical tubes and 4 mL of a 100 Mean log reduction MIC (mM) solution of the antimicrobial compound being tested in sterile Phosphate-buffered saline (PBS) buffer was added
Studies have shown that thymol (1a) and carvacrol (2a) compromise the outer membrane of Gram-negative bacteria increasing the permeability of the cytoplasm (El Abed et al, 2011)
Summary
Pseudomonas aeruginosa is a Gram-negative, rod shaped bacterium with a pronounced tendency to form biofilms. Aromatic alcohols such as phenoxyethanol have shown to increase permeability of the cytoplasmic membrane in E. coli (Gilbert et al, 1977; Fitzgerald et al, 1992) In this communication, thymol (1a), carvacrol (2a), and eugenol (3a) as well as guaiacol are evaluated along with several 2- and 4- allyl, 2-methallyl and 2-n-propyl derivatives (Figure 1). The simple analogs 2-allylphenol (3e) and 2-n-propylphenol (3f) were evaluated for comparative purposes to the aforementioned 2-allyl derivatives of the selected essential oils The purpose of this investigation was to develop structure activity relationships for naturally occurring phenol derivatives and to compare these relationships between planktonic and biofilm modes of bacterial growth
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