Phytochemicals efficacy against planktonic bacteria and biofilms

In the last years, the use of biocides for general disinfection has increased, which has influenced the incidence of antimicrobial resistant microorganisms [1]. Due to evidence on the strong relationship between biocide and antibiotic resistance, there is a real risk in enhancing antimicrobial resistance of clinically relevant organisms [2]. Therefore, the control of microbial growth is of prime importance in the hospital environment, and consequently it is critical to explore novel resources to produce high-level disinfectants. In this study, phytochemical products were explored in terms of microbial growth potential against planktonic and biofilm cells. Minimum inhibitory and bactericidal concentrations (MIC and MBC), for Escherichia coli and Staphylococcus aureus, were determined for selected phytochemicals as well as their influence in biofilm prevention and control. Cinnamaldehyde and eugenol can be considered antimicrobial phytochemicals due to their low MIC and MBC (Table I). However, these products were not so successful when bacteria were adhered to polystyrene surfaces or as a biofilm. Interestingly, cinnamic acid demonstrated total reduction of adhered bacteria (≈5 Log), followed by p-coumaric and caffeic acid for both bacteria and ferulic acid for S. aureus or eugenol for E. coli. Additionally, cinnamic acid action against adhered S. aureus was comparable to peracetic acid and sodium hypochlorite and more effective than hydrogen peroxide (benchmark biocides). Adhered E. coli were more susceptible to cinnamic, p-coumaric and caffeic acids than to the benchmark biocides. The proven effectiveness of several phytochemicals, generally with low cytotoxicity, against bacteria makes them an interestingly alternative to commonly used disinfectants.

Tab. 1: MIC and MBC (mM) for S. aureus and E. coli.

	S. aureus		E. coli
	MIC	MBC	MIC	MBC
Cinnamaldehyde	5	12	3	8
Cinnamic Acid	25	25	15	> 25
Coumaric Acid	25	25	15	> 25
Caffeic Acid	23	> 25	25	> 25
Ferulic Acid	25	> 25	> 25	> 25
Tyrosol	> 25	> 25	> 25	> 25

Keywords: Antimicrobial resistance, Disinfection, Phytochemicals

References:

[1] Reed, D., Kemmerly, S. A. (2009) Infection control and prevention: a review of hospital-acquired infections and the economic implications. Ochsner J. 2009 9:27 – 31.

[2] Fraise, A. P. (2002) Biocide abuse and antimicrobial resistance – a cause for concern? J. Antimicrob. Chemother. 49:11 – 12.