Characterization of Escherichia coli colonizing the gastrointestinal tract and urinary tract catheters

Abstract

Commensal and pathogenic bacteria express biofilm behaviour which is thought to alter bacteria-host interactions and contribute to colonization and persistence. In the current thesis, the epidemiology of biofilm formation in gastrointestinal commensal Escherichia coli and E. coli isolated from urinary catheters is described. Further on, in selected commensal isolates the impact of biofilm formation on the interaction with a gastrointestinal epithelial cell line is investigated. The contribution of selected genes to biofilm formation of E. coli on catheter surfaces is investigated.

Gastrointestinal commensal E. coli were commonly able to express a biofilm behaviour (adherence, pellicle formation and clumps) which was characterized by the expression of the extracellular matrix components curli fimbriae and cellulose as it can be assessed by a distinct colony morphotype on Congo Red agar plates. Expression of the exopolysaccharide cellulose and curli fimbriae was positively regulated by the master regulator of biofilm formation, the transcriptional regulator CsgD, in the commensal strain TOB1. However, in the probiotic E. coli strain Nissle 1917, cellulose production was uncoupled from CsgD expression.

The biologic roles of cellulose and curli fimbriae were investigated by studying the interactions between commensal bacteria and the human gastrointestinal epithelial cell line HT-29. Curli fimbriae expressed by the commensal strain TOB1 enhanced adherence to, internalization by and IL-8 production of the cell line HT-29. Expression of cellulose, which is co-expressed with curli fimbriae in TOB1 at 37 ºC diminished adherence, internalization and IL-8 production. The role of cellulose is different in Nissle 1917. Although expression of cellulose by Nissle 1917 at 37 ºC also suppressed internalization by HT-29 cells, cellulose production had a positive effect on adherence of Nissle 1917 to intestinal epithelial cells and the production of IL-8 in response to the bacteria.

Most bacteria isolated from urinary tract catheters had the capability to adhere to polystyrene surfaces in laboratory medium. However, adherence was highly dependent on environmental conditions and changed with the culture media and the surface. Urine as growth medium generally leads to a decrease in adherence. Bacteria adhered less to the surface of silicone catheters than silicone coated latex catheters. A species dependent pattern of adherence was also observed. Pseudomonas spp. isolates adhered more to the catheter surface than isolates of the other species. Adherence by E. coli strain was correlated with presence of the fluA gene, expression of rough LPS and type 1 fimbriae, but not with the expression of cellulose and curli fimbriae.