Gene transfer.

Is it possible that bartonella can transfer gene resistance to lyme in a body of a infected person? Is it a difficult question...

Bacteria can transfer genes via small chromosomes called plasmids. Borrelia burgdorferi has been found to have as many as 23 plasmids, which is the largest number of plasmids ever reported in a pathogenic bacterium. These plasmids represent genes acquired from other organisms.

Theoretically these plasmids could contain genes for antibiotic resistance, although I'm not aware of any research findings on this.