Resistance towards antibiotics stands out today as a major issue in the clinical act of treatment of bacterial-generated infections. This process was characterized in proteoliposomes reconstituted from an E.coli strain isolated from invasive infections (blood culture) occurred in patients with a cardio-vascular device admitted for surgery. Fluorescence spectroscopy and patch-clamp technique have been used. Two types of antibiotics have been targeted: ceftazidime and ciprofloxacin. Antibiotics addition in proteoliposomes suspension undergoes a quenching in tryptophan residues from outer membrane porins structure, probably due to the formation of a transient non-fluorescent porin-antibiotic complex. Patch-clamp recordings revealed strong ion current blockages for both antibiotics, reflecting antibiotic-channel interactions but with varying strength of interaction. The present study puts forward the mechanism of multidrug-resistance in extended-spectrum beta-lactamase E.coli strains, as being caused by alterations of the antibiotics transport across the porins of the outer bacterial membrane.