Pseudomonas putida IsoF, a biofilm-producing soil bacterium, uses one lux-type Quorum sensing (QS) system as usual for gram-negative bacteria, thus a positive feedback. Later, also a negative feedback was observed, via a QS-controlled signal-degrading enzyme, including a delay. This allows for a more complex behaviour, e.g. a peak or even oscillating behaviour of the QS activity and can be described by delay differential equations. It is well-known that QS may control very different bacterial processes, like pathogeneity, production of public and private goods, but also to some extent resistance against „stressors“. Bacteriophages can attack bacteria and use them for their own reproduction. With first experimental and modelling results of an ODE model for P.putida, some hypotheses about the bacterial resistance against bacteriophages are tested and hint on a partially QS-driven resistance.