Differential effects of oligosaccharides on the effectiveness of ampicillin against Escherichia coli in vitro

The mounting antibiotic resistance emphasizes an urgent need for alternatives. Recent investigations indicate that non-digestible oligosaccharides (NDOs), besides their prebiotic properties, can directly interact with pathogenic bacteria. In this study, the protective effect of alginate-oligosaccharides (AOS), chitosan-oligosaccharides (COS), galacto-oligosaccharides (GOS) and fructo-oligosaccharides, against enteropathogenicEscherichia. coli was investigated. The effect of these NDOs onE. coli growth, adhesion and E. coli-induced inflammatory response (IL-8 release) of HT-29 intestinal epithelial cells were determined in vitro in the presence or absence of ampicillin, using minimum inhibitory concentration (MIC) assay, anti-adhesion assay and ELISA, respectively. At low concentrations 0.5 % and 1%, AOS decreased theE. coli growth, while high GOS concentrations (6%, 8%, 10 %) were effective. Interestingly, the combination of the low concentrations of AOS with ampicillin (2 μg/mL) exerted a 2-fold decrease in the MIC level of ampicillin against E. coli. AOS also concentration dependently reduced the adherence of E. coli to HT-29 cells. The combination of AOS with ampicillin further increased these anti-adhesive properties. Pre-incubation of HT-29 cells with AOS, COS or GOS significantly hampered the E. coli-induced IL-8 release. Current study highlights the direct effects of NDOs onE. coli growth, adhesion and inflammatory responses of HT-29 cells in vitro.