In the many cases where humans have transferred bacteria to a plant, a new case has been reported where the bacteria that cause acne has been transferred to grapevines.
Researchers from Italy analysed bacterial colonies growing on the common grapevine Vitis vinifera in the northeast.
They were shocked to find a relative of exclusively human-seeking pathogen Propionibacterium acnes - that plagues the skin of humans worldwide - living in the bark of the plant.
They believe farmers transferred the pathogen to the plants roughly 7,000 years ago.
"Since then, the bacterium has become entirely plant-adapted, and it can no longer return to its original human host," said researchers from Fondazione Edmund Mach Research and Innovation Center in Italy.
"It has never been discovered that a human bacterium could be adapted to be the guest of a plant cell," author Andrea Campisano was quoted as saying.
Plants containing this bacteria were healthy, suggesting the bacterium has no negative effects on the plants, and may even benefit the grapevines, claimed the study published in the journal Molecular Biology and Evolution.
The discovery could lead to new microbial treatments that could potentially boost the health of grapevines and other commercially important crops.