A recent study has revealed that P.acnes which is already present within the body may be the cause of infections.

"It is important to recognise that this organism has the ability to grow slowly inside our body cells as well as on the surface of medical devices in the body," said Professor Peter Lambert, expert in P.acnes infection from Aston University.
It has long been associated with common acne, where it contributes to the inflammation and pain. Recent studies show that it might also be involved in other important conditions such as prostate cancer."
Source-ANI