Modulating effects of fodder grasses extracts on antibiotic sensitivity and biofilm production in avian pathogenic <i>Escherichia coli</i> strains

Extracts of certain fodder grasses may be viewed as powerful agents against infections induced by avian pathogenic <i>Escherichia coli</i> strains. Here we demonstrated ability of <i>Galega orientalis</i> and <i>Rhaponticum carthamoides</i> extracts, alone or in combination with antibiotics, to inhibit growth, viability and biofilm formation in avian pathogenic <i>Escherichia coli</i> strains with different sensitivity to antibiotics and non-pathogenic laboratory strain <i>E. coli</i> BW25113 as well as its mutant derivatives. Modulation of motility and production of extracellular structures in the presence of the extracts correlated with their anti-biofilm effects. Interestingly, an increase in antibacterial action of kanamycin, streptomycin, ciprofloxacin, and cefotaxime on both biofilms and planktonic cultures of the studied strains was observed in the presence of the extracts, including antibiotic resistant APEC strain #45. The extracts alone showed weak prooxidant activity which could contribute to modification of redox-sensitive sites of various regulatory circuits, resulting to synergetic effects in combination with antibiotics.