10.22376/ijpbs.2019.10.1.p1-12 Volume 2 Issue 3 2011 (July - September) When bacteria grow lessThan i greaterThan in vivo lessThan /i greaterThan , they must cope up with a hostile environment in which certain nutrients are not adequate, and where the host attempts to eliminate them in different ways. In such situations, bacteria use certain survival strategies by forming biofilms. In the present study, an lessThan i greaterThan in vitro lessThan /i greaterThan technique was designed to grow lessThan i greaterThan Escherichia coli lessThan /i greaterThan serotype isolated from bovine mastitis cases, in planktonic mode under nutrient rich condition (3% TSB) and also in biofilm mode, by incorporating bentonite clay (0.3%) under nutrient restricted condition (0.16% TSB). Sequential steps involved in the formation of biofilms lessThan i greaterThan in vitro lessThan /i greaterThan by lessThan i greaterThan E.coli lessThan /i greaterThan were studied by TEM. lessThan i greaterThan E.coli lessThan /i greaterThan grown in planktonic mode had the architecture of rod shape with extracellular appendages. Also, the cells grown in biofilm mode were same as that of cells grown in planktonic mode. In the later stages, bacterium was attached to the surface of bentonite clay. Transition from planktonic state to the biofilm state requires a developmental alteration in flagellae, fimbriae or pili i.e. repression of extracellular appendages and expression of exopolysaccharide leading to formation of microcolonies, a 3-D architecture of mature biofilms (Phase variation).  Kavitha G, S Isloor, D Rathnamma, Y B Rajeshwari, B M Veere Gowda And C S Nagaraja Escherichia coli, planktonic cells, in vitro biofilms, Exopolysaccharide, microcolonies 482-487