Antimicrobial activity of well-dispersed MWCNTs with an average diameter of 10 nm was investigated by analyzing the growth curves of Escherichia coli (E.coli) population in surfactant-modified MWCNTs and polymer-modified MWCNTs in Luria Bertani (LB) broth. MWCNTs can be dispersed in ionic surfactants like sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDDBS), sodium cholate (SC), dodecyltrimethylammonium bromide (DTAB) and decyltrimethylammonium bromide (CTAB), as well as in a non-ionic polymer-polyvinylpyrrolidone (PVP). Good dispersion of surface functionalized MWCNTs was observed by UV-Vis spectroscopy and microscopic techniques. Biocompatibility of these surfactants was estimated by analyzing the growth curves of E. coli population in both surfactant-LB broth and polymer-LB broth. SDDBS and PVP, which showed the least toxicity towards the E. coli cells, were selected to study the interaction of well-dispersed MWCNTs by these materials with bacteria. Observation of the deformed E.coli cell membranes using SEM confirms the antimicrobial activity of MWCNTs.