Abstract
The antimicrobial actions of three common plant-derived terpenoids (i.e., carvacrol, thymol and eugenol) were compared to those of a typical quaternary ammonium biocide (i.e., benzalkonium chloride; BAC), against both planktonic and biofilm cells of two widespread Staphylococcus species (i.e., S. aureus and S. epidermidis). The minimum inhibitory and bactericidal concentrations (MICs, MBCs) of each compound against the planktonic cells of each species were initially determined, together with their minimum biofilm eradication concentrations (MBECs). Various concentrations of each compound were subsequently applied, for 6 min, against each type of cell, and survivors were enumerated by agar plating to calculate log reductions and determine the resistance coefficients (Rc) for each compound, as anti-biofilm effectiveness indicators. Sessile communities were always more resistant than planktonic ones, depending on the biocide and species. Although lower BAC concentrations were always needed to kill a specified population of either cell type compared to the terpenoids, for the latter, the required increases in their concentrations, to be equally effective against the biofilm cells with respect to the planktonic ones, were not as intense as those observed in the case of BAC, presenting thus significantly lower Rc. This indicates their significant anti-biofilm potential and advocate for their further promising use as anti-biofilm agents.
Highlights
Staphylococcus aureus is a common facultative anaerobic Gram-positive bacterial pathogen associated with a wide spectrum of minor to serious community and hospital-acquired infections.This non-motile, catalase and coagulase positive coccus is equipped with a tremendous range of virulence factors which allow its survival within the living host [1]
With respect to the efficiency of the terpenoids (i.e., CAR, THY, and EUG) against the biofilm cells, someone observes that the minimum biofilm eradication concentrations (MBECs) against S. aureus were always two-fold lower compared to those observed against S. epidermidis, something that implies that S. aureus biofilm was less hard to eradicate using those compounds compared to that formed by S. epidermidis
The MBEC of Benzalkonium chloride (BAC) against S. aureus was two times more than that observed against S. epidermidis, indicating that S. aureus biofilm was less susceptible to BAC compared to S. epidermidis one
Summary
Staphylococcus aureus is a common facultative anaerobic Gram-positive bacterial pathogen associated with a wide spectrum of minor to serious community and hospital-acquired infections. This non-motile, catalase and coagulase positive coccus is equipped with a tremendous range of virulence factors which allow its survival within the living host [1]. S. epidermidis is usually a harmless commensal bacterium highly abundant on the human skin playing an important role in balancing the normal microflora. This can still switch to an invasive lifestyle under certain predetermined conditions. This has still emerged as the most frequent cause of nosocomial infections primarily in patients with indwelling medical devices [4]
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