Antibacterial Activity of Phenolic Compounds: P-Coumaric Acid, Caffeic Acid, Cinnamic Acid and Gallic Acid

Abstract

Antimicrobial resistance is one of the most important human and animal health threatening issues worldwide. Therefore, one of the future perspectives to reduce the use of antibiotics might be natural bioactive materials [1]. Natural phenolic acids are known by their anti-inflammatory, antibacterial and antioxidant effect. However, just one research study has analysed the antimicrobial activity of gallic acid, caffeic acid and pyrogallol in isolated bacteria [2]. The aim of this study was to evaluate antibacterial activity of phenolic compounds (PC) in bacteria isolated from infected skin wounds. The study was done at the Lithuanian University of Health Sciences, Veterinary Academy from December 2021 to March 2022. PC antibacterial activity was evaluated in vitro by the method diffusion in agar. Mueller-Hinton agar was used. Reference (Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC 29212), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27859)) and clinical (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa isolated from dogs and cats wounds) bacteria were used. The Petri plates with different concentration (from 5 % to 1 %) of p-coumaric acid, caffeic acid, cinnamic acid and gallic acid were incubated at 37 °C for 24 h. 96° ethanol was used for positive control, and purified water for negative control. For each strain, 5 plates were used. After incubation the antibacterial activity was assessed by measuring the clear zone in millimetres around the well. Statistical analysis was done by SPSS 27.0 software, assessing median, minimum and maximum values; p values were counted by Mann-Whitney U test. All 5 % conc. PC presented antibacterial activity. P-coumaric acid presented the greatest effect in ref. S. aureus (27.50 [22-30]), E. faecalis (19 [14-22]) and clinical S. aureus (21.50 [12-30]), E. faecalis (16.50 [14-20]). Caffeic acid presented the greatest effect in ref. S. aureus (27 [11-30]), E. faecalis (18 [10-21]) and clinical S. aureus (23 [20-24]), E. faecalis (16.50 [14-20]). Cinnamic acid presented antibacterial activity just in ref. S. aureus (23 [20-28]) and E. faecalis (15 [14-15]). Gallic acid presented the greatest activity just in ref. S. aureus (12.50 [10-29]). P-coumaric acid and caffeic acid had no difference in antibacterial activity of reference S. aureus (U=34, p=0.4), E. faecalis (U=25, p=0.190) and clinical S. aureus (U=27, p=0.792), E. faecalis (U=24, p=0.562). P-coumaric acid presented 2.2 times higher effect in ref. S. aureus than gallic acid (U=8,.5, p=0,.003). The lower concentration of PC presented antibacterial activity just in S. aureus strain. 4 % conc. p-coumaric acid presented activity in ref. (20 [13-23]) and clinical (12 [11-19]) S. aureus. In ref. S. aureus p-coumaric acid, cinnamic acid and gallic acid had no differences in antibacterial activity (U=9, p=0.905; U=5, p=0.286). Of all PC just 1 % conc. gallic acid presented antibacterial effect in ref. S. aureus (15 [11-17]). According to the findings, the tested phenolic compounds presented antibacterial activity. The highest effect was found in S. aureus and E. faecalis, both reference and clinical strains. For further tests more studies, such as cytotoxicity evaluation of substances, are necessary.