Hydrophobic properties of the rabbit enteric pathogen Escherichia coli strain RDEC-1

Abstract

Escherichia coli strain RDEC-1 (serotype 0.15: H- ) is a rabbit pathogen which attaches to the intestinal mucosa in a manner that is morphologically identical to the binding of enteropathogenic E. coli in the intestine of human infants. The organisms express mannose-resistant bacterial lectins previously defined as attachment factor, rabbit-1 (AF/R1) pili. We examined the effect of AF/R1 pilus expression on the hydrophobicity of RDEC-1. Hydrophobicity was determined by four complementary methods: the salt aggregation test, hydrophobic interaction chromatography, adherence to polystyrene, and contact angle with water measurements. The organisms were more hydrophobic when AF/R1 pili were expressed compared with bacteria grown to suppress pilus expression. Binding of bacteria to polystyrene surfaces was dependent on AF/R1 pilus expression. Attachment of piliated RDEC-1 to more hydrophilic surfaces such as sulphonated polystyrene was minimal. Adherence of piliated E. coli to polystyrene was reduced by 80% when propanol was added to reduce the surface tension of the suspending buffer. Conversely, in the presence of propanol adherence of piliated organisms to sulphonated polystyrene increased 12-fold. The data indicate that AF/R1 pilus expression increased the cell surface hydrophobicity of E. coli RDEC-1. In addition, expression of the hydrophobic adhesins mediated bacterial attachment to hydrophobic surfaces.