Background: The continuous rise of resistant E. coli, originating from urine samples, leads to increasing therapeutic challenges. In the vast majority of cases, ESBL-positive E. coli are the main problem. Also AmpC-ß-lactamase can be responsible for resistance and both, ESBL and AmpC-ß-lactamase, can cause a Cefotaxim resistance. The combination of a ß-lactam antibiotic with a ß-lactamase-inhibitor is a therapeutic option and remains a topic of discussion. The aim of this study was a resistance-testing of four different combinations of ß-lactam antibiotic with a ß-lactamase-Inhibitor.Methods: 100 consecutive E. coli isolates from urine samples, which show Cefotaxim resistance in disc diffusion test according to EUCAST, were collected from January to March 2016. MIC test strip (Liofilchem®) were used to determine the MICs of the following drugs: Amoxicillin/Clavulanic acid (Amo/Cla), Ampicillin/Sulbactam (Amp/Sul), Piperacillin/Tazobactam (Pip/Taz) and the recently introduced Ceftolozane/Tazobactam (Cef/Taz). The testing procedure was performed according to the manufacturer instruction and interpretation was made using EUCAST-guideline from 2016.Results: All isolates showed an ESBL-production as the mechanism of resistance. No AmpC-production could be detected. Within the substances, which can be administered orally (Amo/Cla, Amp/Sul), remarkable differences can be detected. While an efficiency of 34% in complicated (MIC 8) respectively 74% in uncomplicated (MIC 32) urinary tract infection could be determined for Amo/Cla, Amp/Sul shows an efficacy of 26%. The parenteral administered combinations on the other hand provide a good activity (Pip/Taz 94%, Cef/Taz 95%).Discussion: The predominant problem of resistant E. coli from urine samples is caused by ESBL-production. The orally administered drug combinations (Amo/Cla, Amp/Sul) show a limited activity, while the parental combinations (Pip/Taz, Cef/Taz) show a good in vitro activity.