In previous studies, the multidrug efflux system, AcrAB, of the fire blight pathogen, Erwinia amylovora, had been investigated suggesting that this system is required for in planta survival and phytoalexin tolerance. Later on, the third component of the AcrAB system, the outer membrane protein TolC, was under investigation. For TolC, a direct involvement in multidrug efflux could be demonstrated. Mutants defective in tolC were impaired in in planta survival and showed a significantly reduced tolerance to phytoalexins, such as phloretin. Interestingly, there was an additional phenotype for the tolC knockout: A protein of approximately 55 kDa was not secreted from mutant anymore. Currently, the group investigates both, the role and the transcriptional regulation of this protein. The study is done in close cooperation with the group of Dr. Helge Weingart (University Lecturer in Biotechnology) at Jacobs University Bremen.