10.22376/ijpbs.2019.10.1.p1-12 Volume 6 Issue 4 2015 (October - December) Quorum sensing (QS) is well known for bacterial cell to cell dependent mechanism and its stimulus response are correlated to population density. Quorum sensing inhibition can reduced the risk of microbial pathogenicity in all infection. In this study methanolic leaf extract of lessThan i greaterThan Plectranthus amboinicus lessThan /i greaterThan was assessed for its anti quorum sensing activity against Acyl Homoserine Lactone (AHL)-dependent virulence factor inhibition in all bacterial pathogens [ lessThan i greaterThan Serratia marcescens, lessThan /i greaterThan lessThan i greaterThan Pseudomonas aeruginosa, lessThan /i greaterThan lessThan i greaterThan Vibrio harveyi lessThan /i greaterThan (MTCC 7771) lessThan i greaterThan , Hafnia alvei lessThan /i greaterThan (MTCC 1426)] at the concentration of 50mg/ml. In addition the methanolic leaf extract lessThan i greaterThan Plectrantus amboinicus lessThan /i greaterThan showed no growth inhibitory effect on bacterial pathogens. The methanolic leaf extract of lessThan i greaterThan Plectrantus amboinicus lessThan /i greaterThan have also inhibited the rhamnolipid production in lessThan i greaterThan Pseudomonas aeruginosa lessThan /i greaterThan and controlled the swimming and swarming motility in lessThan i greaterThan Serratia marcescens lessThan /i greaterThan . In lessThan i greaterThan Vibrio harveyi lessThan /i greaterThan (MTTC 7771) the bioluminescence was controlled by lessThan i greaterThan Plectranthus amboinicus lessThan /i greaterThan at the concentration of 50mg/ml. Hence it was envisaged that the methanolic leaf extract of lessThan i greaterThan Plectrantus amboinicus lessThan /i greaterThan could pave the way to prevent quorum sensing (QS) mediated bacterial infections. R. NANCY IMMACULATE MARY AND N. BANU Antiquorum sensing, Biofilm, Rhamnolipid, Motility, Bioluminescence 1060-1068