* To whom all correspondence should be addressed. Tel: +201282854531, Fax:+2033911793; E-mail: Fadymicro@yahoo.com JOURNAL OF PURE AND APPLIED MICROBIOLOGY, March 2016. Vol. 10(1), p. 121-128 Novel Medical Properties of Cinnamomum zeylanicum Oil against Pseudomonas aeruginosa Fady F. Abd El-Malek, Amany S. Youssef and Samy A. El- Aassar Department of Microbiology, Faculty of science, Alexandria University, Egypt. (Received: 10 July 2015; accepted: 06 September 2015) Cinnamon oil has variety of medical properties against several types of Gram- positive and Gram-negative bacteria, several recent studies deals with the common medical properties of cinnamon oil and its application on infection control and wound management. Methods: This study illustrates new medical properties of cinnamon oil against one of the most virulent pathogens which is an opportunistic organism; P. aeruginosa a Gram-negative pathogens with several virulence factors that we will deal with and how cinnamon oil can overcome its activity. In this study we focus on the virulence activity of P.aeruginosa and how it can be a main reason of chronic wounds infection, inflammation and necrosis. The clinical isolates under investigation in this study are pathogenic isolated from different wounds, ulcers and bed sores from patients of Alexandria university hospitals. These new medical properties of cinnamon oil can hinder the pathogenic properties of P.aeruginosa through facing its virulence factors and thus achieving of complete recovery. Key words: Virulence factors, Proteolysis, Haemolysis, antibacterial, anti-proteolytic. Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that may be isolated from different habitats, it is characterized with high survival rate due to its high adaptability and ability to resist antibiotic activity, and it may cause severe infections as severe burns, diabetic foot infections, bed sores, eye infection and cystic fibrosis (CF). The treatment of P. aeruginosa becomes very limited due to the increase of antimicrobial agents resistance which leads to high rate of resistance (Lyczak et al. 2000). The incomplete recovery of an acute infection with P. aeruginosa may lead to a chronic infection with an increase in biofilm formation (Williams et al . 2010). The isolation of P. aeruginosa from acute infections is different from those isolated from chronic infections in phenotype (Smith et al. 2006). The comparison between isolates which are isolated from acute infections that lack some of the virulence factors from those isolated from chronic infections, in other hands pathogens from chronic infections may lack some of the inflammatory virulence factors such as flagella and pili, but instead it has other virulence mechanisms as type 3 secretion system (T3SS) which contain different exotoxins (ExoU, ExoS, ExoT and ExoY) (Hogardt & Heesemann 2010). P. aeruginosa isolates from chronic infections can form biofilms which are mucoidal because of the exopolysaccharide alginate (Sadikot et al. 2005; Kipnis et al. 2006). In biofilms bacteria are attached to each other in a highly organized structure to the surface of the infected tissue linked with quorum sensing (Bjarnsholt et al. 2010), this structure consists of extracellular polymeric substances (EPS) which are formed from polysaccharides, nucleic acids, lipids, and proteins