pierre, I am not a specialist in this but I would think they...

pierre, I am not a specialist in this but I would think they used normal human cell cultures. Weather there is a need for human studies I do not know. As you know we determine the antibiotic resistance almost always in vitro, not usually in animals or never in humans when selecting what is the best drug against the bacteria. The important issue is that the drug does not harm the patient. Today, however, we know that all of us have billions of bacteria in our gut. The phase 2 study with PBT2 demonstrated that during the 2 years there were not any superinfections, at least not reported.  
To me it looks like that the in vitro studies are enough together with the phase 1 and phase 2  studies with PBT2. In any case when treating an infection the treatment will usually last only max few weeks.