Hydrophobicity and Biofilm Growth of E-coli RP437, MG1655 and B/r
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Hydrophobicity and Biofilm Growth of E-coli RP437, MG1655 and B/r Li Hong Zhao and Pabitra N. Sen Department of Physics and Astronomy, The University of North Carolina, Chapel Hill NC 27599 ABSTRACT Two strains of E-Coli K-12, viz, RP437, MG1655 and B/r (E. coli B derivative, not a K12 strain) were grown on various surfaces to study bacterial adhesion and subsequent biofilm formation. We observed biofilm and large colonies on cover slides, beads made of soda lime or borosilicate glasses, on plasma treated PDMS (Polydimethylsiloxane), on Tissue Culture (TC) polystyrene, and observed some clusters on plasma treated ZnTi cover slide; but no evidence of biofilm on untreated-PDMS and ZnTi glass cover slides. From contact angle measurements, we conclude that the hydrophobic nature of untreated PDMS prevent bacterial adhesion for these three strains. INTRODUCTION Biofilms are ubiquitous growths of bacteria in a form designed by nature to be highly robust and resistant to all forms of environmental stresses. Biofilms are the “city of microbes” [1] where community of bacteria adhere to a surface and encapsulate themselves in an extracellular matrix (ECM), that they produce by the up and down-regulation of specific genes [2]. ECM consists of extracellular polysaccharides (EPS), DNA, proteins etc. The biofilms are dynamic and are well constructed for growth, nutrient passage, and future detachment of a sub colony [1,2]. The size, the detailed structure and the composition of the ECM vary greatly even for strains within the same species, and are influenced by nutrient, concentration and flow. As a biofilm, the bacterial colony seems to gain super powers and cause havoc everywhere. They can grow up to several centimeters thick and cover large areas. It is now believed that bacteria exist mostly as biofilms and not in its planktonic form [1,2]. According to NIH, 80% of all microbial infections in the body involve biofilm and are remarkably difficult to treat with antimicrobials. The biofilms are behind numerous infections-- urinary tract to catheter to middle ear, to name a few. They affect contact lenses, pacemakers in heart, dental plaques, and even in computer chips, hulls of ships, oil pipelines, and a numerous other microbial fouling. A better understanding of biofilm processes would help develop control strategies to ameliorate its super powers leading to improvement in health, engineering and environmental management. It is believed that bacteria communicate via quorum sensing to design, build, and communicate, within the “city of microbes” and function as a cooperative consortium via transcriptional activator quorum-sensing signaling molecules [1,2]. The triggering of gene regulations dependent on the concentration of the signaling molecules and hence on the geometry confining the bacteria. Our original intention was to study the effect of crowding and quorum-sensing using controlled microfluidic devices using PDMS. Arguably, PDMS is the most popular material that is used for fabricating microfluidic devices. PDMS is uniq
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