Investigation of in vitro antimicrobial activities of some hydroxybenzoic and hydroxycinnamic acids commonly found in medicinal and aromatic plants

Since hospital-acquired microorganisms are developing more and more resistance to antibiotics used today, researchers are turning to new searches in the treatment of infectious diseases. Unfortunately, unconscious use of antibiotics is another important reason why microorganisms develop resistance to infectious diseases. The aim of this study was to test the antimicrobial activity of some hydroxybenzoic and hydroxycinnamic acids on various gram-positive and gram-negative bacteria and a yeast strain (C. albicans). Agar well diffusion and minimum inhibitory concentration (MIC) tests were applied to determine the antimicrobial activities of phenolic acids. Considering the activity findings of phytochemicals on all test microorganisms, they were ranked in terms of their activities with a statistical method called the relative inhibitory capacity index (RICI) (a method that was first introduced in the literature by the current study). RICI analysis showed that the most effective phenolic acids for all test microorganisms were sinapic acid and 4-hydroxybenzoic acid. The RICI coefficients of these compounds were 1.02 and 0.99, respectively. Sinapic acid exhibited a zone of inhibition of 9.00-27.00 mm and an MIC of 18.00-72.00 mg/ml on microorganisms. Inhibition zone and MIC value ranges of 4-hydroxybenzoic acid were determined as 9.00-16.00 mm and 36.00-72.00 mg/ml, respectively. RICI analyzes confirmed that 2-phenylbutyric acid and phloroglucinol carboxylic acid did not show any antimicrobial activity. It is thought that sinapic acid and 4-hydroxybenzoic acid can be used as alternative antimicrobial agents against multi drug resistant microorganisms