Studies on biofilm formation by Escherichia coli O157:H7

This study was conducted to determine the influence of cultural conditions on biofilm formation by Escherichia coli O157:H7, the effects of chemical agents on initial attachment and established biofilms, the efficacy of sanitizing agents, and the bacterial structures involved in the process.; Biofilms were developed on stainless steel chips in Trypticase soy broth (TSB), 1/5 TSB, 0.1% Bacto peptone and a minimal salts medium (MSM). Biofilms developed faster and contained a higher number of adherent cells when the organisms were grown in the low nutrient media. Biofilms developed in MSM consisted of short cells with thicker extracellular polysaccharide (EPS). Low numbers of bacteria in the initial attachment step and non-hydrophobicity of the cells contributed to poor biofilm formation in TSB. EPS is important for the biofilm stability at 22-{dollar}27spcircrm C{dollar} but not at {dollar}10spcircrm C{dollar} and under anaerobic conditions.; Chemical agents were added during the initial attachment process and to established MSM biofilms to determine bacterial structures involved. Concanavalin A, pronase E, proteinase K, EDTA, EGTA, deoxycholic acid, and Tween 20 decreased bacterial attachment. Partial removal of biofilm bacteria was observed with Tween 20, EDTA, sodium metaperiodate, benzalkonium chloride and cetyl trimethyl ammonium bromide (CTAB); in addition, benzalkonium chloride and CTAB inactivated biofilm bacteria. Outer membrane proteins (OMPs), fimbriae and lipopolysaccharide (LPS) probably mediate bacterial attachment. LPS and EPS are important in biofilm establishment.; EPS and OMPs of biofilm and planktonic bacteria were analyzed by high performance liquid chromatography and SDS polyacrylamide gel electrophoresis, respectively. Biofilm cells produced EPS containing rhamnose and glucuronic acid. Low amounts of EPS produced by TSB biofilms explains poor biofilm formation in this medium. The EPS may also function in attachment because it was also produced by MSM-grown planktonic cells. TSB-grown planktonic cells elaborated a different EPS containing rhamnose, glucuronic acid, mannose and glucose which did not play a role in biofilm formation. OMPs of biofilm and planktonic bacteria showed similar banding patterns, suggesting that OMPs did not play a significant role in biofilm establishment.; Biofilm bacteria were more resistant to sanitizers than their planktonic counterparts. Iodine was effective in inactivating biofilm bacteria.