10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 2 2013 (April - June) lessThan i greaterThan Pseudomonas aeruginosa lessThan /i greaterThan and lessThan i greaterThan Acinetobacter baumannii lessThan /i greaterThan are common nosocomial pathogens, well recognized for their multidrug resistance. Acyl-homoserine lactone (Acyl-HSL) based Quorum sensing (QS) is known to regulate virulence and biofilm maturation in these organisms; hence, inhibition of QS will help to control their pathogenicity. In the study, 5 plants, lessThan i greaterThan Rubia cordifolia lessThan /i greaterThan , lessThan i greaterThan Tinospora cordifolia lessThan /i greaterThan , lessThan i greaterThan Picrorhiza kurroa lessThan /i greaterThan , lessThan i greaterThan Cassia fistula lessThan /i greaterThan and lessThan i greaterThan Bauhinia variegata lessThan /i greaterThan were screened for QS inhibition. A comparison of different extracts from the above plants, for short and long acyl-HSL inhibition in both pathogens, was carried out using reporter strains, lessThan i greaterThan Chromobacterium violaceum lessThan /i greaterThan ATCC12472 and lessThan i greaterThan Escherichia coli lessThan /i greaterThan MG4/pKDT17 respectively. Ethyl acetate extracts of lessThan i greaterThan T. cordifolia lessThan /i greaterThan inhibited short as well as long acyl-HSLs with about 78% & 71% inhibition of long acyl-HSLs in lessThan i greaterThan P. aeruginosa lessThan /i greaterThan and lessThan i greaterThan A. baumannii lessThan /i greaterThan respectively; higher than the positive control, garlic extract (29% and 33% respectively). Further, absence of antibacterial activity of the plant extract confirmed its QS inhibitory potential. VIRAJ GALA, NITHYA JOHN AND KRUTIKA DESAI Acyl homoserine lactone, Quorum sensing, Pseudomonas aeruginosa, Acinetobacter baumannii, Tinospora cordifolia 445-453