505 J. Indian Chem. Soc., Vol. 92, April 2015, pp. 505-508 Antibacterial activity of plant essential oil microemulsion against wound isolate Macrococcus caseolyticus Vijayalakshmi Ghosh, Amitava Mukherjee and Natarajan Chandrasekaran* Centre for Nanobiotechnology, VIT University, Vellore-632 014, Tamilnadu, India E-mail : nchandrasekaran@vit.ac.in Abstract : Microemulsion is colloidal dispersion of oil and water having droplet size in the range of 2–50 nm and is stabilized by the interfacial layer of surfactant. Antibacterial application of microemulsion in prevention of wound in- fection is not much explored. Previous work by our group has demonstrated the role of surfactant concentration in determining the droplet diameter, optical property and the stability of microemulsion. Also, the formulated microemulsion triggered the wound healing process in wistar rats. In the present work, selected microemulsion formulation (CMF4 : droplet size = 5.79 nm; oil/surfactant/water composition = 6/24/70 (vol/vol)) demonstrated bactericidal activity against wound isolate Macrococcus caseolyticus (confirmed by 16S rDNA sequencing). Inactivation kinetics exhibited time and dose dependent killing of Macrococcus caseolyticus by CMF4 microemulsion. Complete loss of Macrococcus caseolyticus viability was observed after incubating with 10-fold diluted CMF4 microemulsion formulation for 20 min. The CMF4 microemulsion also exhibited antibacterial activity at higher dilution of 1000-fold. FTIR study illustrated alteration of functional groups of Macrococcus caseolyticus surface upon CMF4 microemulsion treatment. Scanning electron micros- copy images illustrated the morphological changes in Macrococcus caseolyticus after interaction with CMF4 microemulsion. The outcome of the presented study suggested CMF4 microemulsion may be applied for prevention of infection in wound management. Keywords : Microemulsion, cinnamon oil, bacterial activity, wound isolate, Macrococcus caseolyticus. Introduction From a microbiological point of view, the major func- tion of skin is to control bacteria population that survives on the surface of skin and to prevent underlying tissue from pathogen invasion and colonization. Wound is an injury to the skin which leads to exposure of the underly- ing epithelial tissue to the environment and also to the microbial population. Injury to skin i.e. wound also pro- vides a nutritious medium for proliferation of bacteria. Hence the wound site becomes prone to microbial growth and infection of surrounding tissue. Wound management aims at preventing wound from infection/sepsis and helps in triggering wound healing process. Popular antibacterial agents like colloidal silver-im- pregnated dressing materials, silver sulfadiazine, mafenide acetate and neomycin are reported to have several draw- backs including uneven potential to penetrate into the es- char; possible toxicity to the host immune tissues and differential efficacy against both Gram-negative and Gram- positive bacteria 1 . Plant essential based microemulsion formulations could be the possible solution for the above mentioned problem. Plant essential oils are rich source of bioactive volatile compounds that results in different ap- plication purposes. Cinnamon essential oil is reported to be one of the richest sources of cinnamaldehyde and eu- genol that provides property to the oil 2,3 . Cinnamon es- sential oil can be extracted from cinnamon bark as well as leaf. Microemulsions are thermodynamically stable nano- dispersions of oil and water with droplet size ranging between 2–50 nm and stabilized by surfactants and/or co- surfactants 4 . Due to their very low droplet size micro- emulsion scatter light waves very imperceptibly and hence they are optically transparent. Also the reduced droplet size the active ingredients penetrate deep into the tissue and enhance bioavailability. In our previous study, we optimized process param- eters for development antimicrobial microemulsion sys- tem with cinnamon leaf oil, Tween 20 and water for wound healing application 4 . Aim of the present study is to study JICS-11