Enhanced activity of carvacrol against biofilm of Staphylococcus aureus and Staphylococcus epidermidis in an acidic environment

Carvacrol is an antimicrobial monoterpenic phenol which occurs in many plant essential oils. The aim of this study was to investigate its activity at acidic pH on staphylococcal forming and yet established biofilms, with particular focus to improve its effectiveness on Staphylococcus epidermidis biofilm. The results showed that the subinhibitory doses (1/2, 1/4 and 1/8 MIC) of carvacrol deter- mined a higher reduction of S. epidermidis biofilm formation than that observed at neutral pH. A potentiated inhibitory effect was also observed on established biofilm, carvacrol caused either a strong reduction of biomass (>50%) and bacteria attached to polystyrene (>7 log units). The images of scanning electron microscopy and the gas-chromatographic analysis support these results. The development of acidic formulations containing carvacrol could be an important tool to control the staphylococcal biofilm in the medical and food environment.