10.22376/ijpbs.2019.10.1.p1-12 Volume 8 Issue 1 2017 (January - March) The antibacterial activities of methanol extracts of lessThan i greaterThan Caulerpa racemosa lessThan /i greaterThan (Forsk) lessThan i greaterThan , Caulerpa sertularioides lessThan /i greaterThan (Gmelin) Howe, lessThan i greaterThan Ulva lactuca lessThan /i greaterThan Linn lessThan i greaterThan , lessThan /i greaterThan lessThan i greaterThan Padina gymnospora lessThan /i greaterThan (Kutzing) Sonder. lessThan i greaterThan , Dictyota dichotoma lessThan /i greaterThan (Hudson) Lamouroux. and lessThan i greaterThan Gracilaria multipartita lessThan /i greaterThan (Clemente) Harvey lessThan i greaterThan lessThan /i greaterThan against lessThan i greaterThan lessThan /i greaterThan bacterial strains lessThan i greaterThan viz., lessThan /i greaterThan lessThan i greaterThan Staphylococcus aureus, lessThan /i greaterThan lessThan i greaterThan Escherichia coli, lessThan /i greaterThan lessThan i greaterThan Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis lessThan /i greaterThan and lessThan i greaterThan Salmonella enterica lessThan /i greaterThan were studied by using disc diffusion method, determination of MIC and MBC. The methanol extracts of lessThan i greaterThan P. gymnospora lessThan /i greaterThan and lessThan i greaterThan D. dichotoma lessThan /i greaterThan showed the highest antibacterial activity against all the bacterial strains tested. The mean zones of inhibition produced by the extracts in agar disc diffusion assays were from 6.3 to 19.5 mm. The MIC was between 125 and 500 μg/ml and MBC was between 250 and 1000 μg/ml. The highest mean zone of inhibition (19.5 mm) was observed with methanol extract of lessThan i greaterThan Padina gymnospora lessThan /i greaterThan against lessThan i greaterThan S. aureus lessThan /i greaterThan lessThan i greaterThan . lessThan /i greaterThan The lowest MIC (125 µg/ml) and MBC (250 µg/ml) values were observed in methanol extract of lessThan i greaterThan P. gymnospora lessThan /i greaterThan and lessThan i greaterThan D. dichotoma lessThan /i greaterThan against lessThan i greaterThan S. aureus lessThan /i greaterThan . These finding suggest that methanol crude extract of lessThan i greaterThan P. gymnospora lessThan /i greaterThan have potential antibacterial activity. Dr.R.VEERAMOHAN, G. ADAIKALA RAJ, M. AND V. VENKATESALU Marine macroalgae, Antibacterial activity, MIC, MBC 136-142