Antimicrobial efficacy of chlorhexidine digluconate alone and in combination with eucalyptus oil, tea tree oil and thymol against planktonic and biofilm cultures of Staphylococcus epidermidis

Objectives Effective skin antisepsis and disinfection of medical devices are key factors in preventing many healthcare-acquired infections associated with skin microorganisms, particularly Staphylococcus epidermidis. The aim of this study was to investigate the antimicrobial efficacy of chlorhexidine digluconate (CHG), a widely used antiseptic in clinical practice, alone and in combination with tea tree oil (TTO), eucalyptus oil (EO) and thymol against planktonic and biofilm cultures of S. epidermidis. Methods Antimicrobial susceptibility assays against S. epidermidis in a suspension and in a biofilm mode of growth were performed with broth microdilution and ATP bioluminescence methods, respectively. Synergy of antimicrobial agents was evaluated with the chequerboard method. Results CHG exhibited antimicrobial activity against S. epidermidis in both suspension and biofilm (MIC 2–8 mg/L). Of the essential oils thymol exhibited the greatest antimicrobial efficacy (0.5–4 g/L) against S. epidermidis in suspension and biofilm followed by TTO (2–16 g/L) and EO (4–64 g/L). MICs of CHG and EO were reduced against S. epidermidis biofilm when in combination (MIC of 8 reduced to 0.25–1 mg/L and MIC of 32–64 reduced to 4 g/L for CHG and EO, respectively). Furthermore, the combination of EO with CHG demonstrated synergistic activity against S. epidermidis biofilm with a fractional inhibitory concentration index of <0.5. Conclusions The results from this study suggest that there may be a role for essential oils, in particular EO, for improved skin antisepsis when combined with CHG.

The influence of environmental factors on the growth of lichens in the field

The majority of studies of the effects of environmental factors on lichen growth have been carried out in the field. Growth of lichens in the field has been measured as absolute growth rate (e.g., length growth, radial growth, diameter growth, area growth, or dry weight gain per unit of time) or as a relative growth rate, expressed per unit of thallus area or weight, e.g., thallus specific weight. Seasonal fluctuations in growth in the field often correlate best with changes in average or total rainfall or frequency of rain events through the year. In some regions of the world, temperature is also an important climatic factor influencing growth. Interactions between microclimatic factors such as light intensity, temperature, and moisture are particularly important in determining local differences in growth especially in relation to aspect and slope of rock surface, or height on a tree. Factors associated with the substratum including type, chemistry, texture, and porosity can all influence growth. In addition, growth can be influenced by the degree of nutrient enrichment of the substratum associated with bird droppings, nitrogen, phosphate, salinity, or pollution. Effects of environmental factors on growth can act directly to restrict species distribution or indirectly by altering the competitive balance among different species in a community.