en Microbiology and Anatomy Microbiology and Anatomy Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine Pseudomonas aeruginosa EF2, ATCC 9027 and ATCC 19660 were grown in a continuous culture under Tween 80 (polyoxyethylene sorbitan monooleate) limitation and optimum conditions (pH 6.5, 37°C at dilution rate of 0.05/h). Culture supernatants were carefully removed and stored at -20°C. To purify the lipases, the culture supernatant was reduced in volume to approximately 10 mL by an ultrafiltration unit. Excess salts were removed and extracellular lipase was purified. Biochemical characterization and SDS polyacrylamide gel electrophoresis suggested that lipase particles consisted of protein and carbohydrate-including lipopolysaccharide-with the major enzyme activity being lipase. Lipase activity was measured as the rate of standard olive oil (predominantly triolein) hydrolysis. Characterization of the purified extracellular lipases was then investigated by hydrolysis activity, interesterification reactions and effect on the chemotaxis and chemiluminescence reactions on human peripheral blood neutrophils and monocytes. It was shown that lipase from the EF2 strain was the most effective enzyme used and monocytes were much more sensitive to lipases than neutrophils. Since monocytes are one of the most important cells of the host defence system, lipase activity of Pseudomonas aeruginosa may contribute to the pathogenesis of infections caused by this Gram-negative bacterium. 229 236 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-356&slc_lang=en&sid=1 MOHAMMAD HAJJARTABAR 20031947532846005099 20031947532846005099 Yes From the Department of Microbiology, School of Medical Sciences, Tarbiat Modarres University NASSER GHAEMI 20031947532846005100 20031947532846005100 No , the Faculty of Sciences, Tehran University, Tehran, Islamic Republic of Iran NASRIN MOAZZAMI 20031947532846005101 20031947532846005101 No From the Department of Microbiology, School of Medical Sciences, Tarbiat Modarres University MAHSHID FAGHlHI-SHIRAZI 20031947532846005102 20031947532846005102 No the Food Research Institute, Vic 3030, Australia.