Cinnamic acid in the control of planktonic and sessile cells of Escherichia coli and Staphylococcus aureus

Abstract

Surface disinfection is one of the frontline strategies to prevent infectious diseases. However, the emergence of resistance against the commonly used biocides has lead to an increasing demand for new antimicrobial compounds. Furthermore, there is strong evidence of a possible relationship between resistance to biocides and cross-resistance to antibiotics. Consequently, the effective control of bacterial growth is of prime importance. Therefore, it is critical to explore new resources to produce effective biocides and plant secondary metabolites (phytochemicals) are an interesting and sustainable source of new bioactive molecules. In this study, two phytochemicals, cinnamic acid and ferulic acid, were tested for their antimicrobial properties in comparison with two commonly used disinfectants, sodium hypochlorite and hydrogen peroxide. Minimum inhibitory and bactericidal concentrations (MIC and MBC), for Escherichia coli and Staphylococcus aureus, were determined for the selected phytochemicals. The effects of the selected antimicrobials were also assessed on monolayer adhered bacteria and on biofilm prevention by colony forming units (CFU) determination.One of the benchmark disinfectants, hydrogen peroxide, was not successful in controlling adhered and biofilm cells of S. aureus. Contrarily, sodium hypochlorite was the most efficient chemical with almost 100% CFU reduction achieved for adhered and biofilm cells of S. aureus and E. coli. Regarding the chosen phytochemicals, ferulic acid was only capable of reducing aproximatly 3 log CFU/cm2 of monolayer adhered E. coli, being inneffective against E. coli biofilms and adhered and biofilms of S. aureus. Curiosly, the effciency of cinnamic acid was comparable to sodium hypochlorite in controlling adhered bacteria, despite its higher MIC and MBC (Table 1). In fact, total CFU reduction was achieved for the monolayer adhered cells of both bacteria. A mild CFU redution of biofim cells was obtained.The overal results demonstrate that cinnamic acid has antimicrobial activity against a Gram-positive and a Gramnegative bacterium. This phytochemical is able to effectively control monolayer adhered bacteria and reduce significantly the viability of biofilms, to values comparative to those obtained with sodium hypochlorite application. Moreover, this study reinforces that phytochemicals are an auspicious alternative to commonly used disinfectants for general disinfection practices.