How my quadrupel turned into an oud bruin

This week I tasted a bottle of a quadrupel I brewed 2 months ago, and was surprised to discover a slight sourness. Not bad at all, it tasted a bit like Rodenbach, or Oerbier. However, it was not supposed to be there, which makes it an infection. I suppose this is what can happen if you brew during summer. I put a drop of the dregs under the microscope and found it to be a pediococcus infection. Luckily the taste is realy nice, so I won't pour it down the drain. Below a picture of the dregs: