eReply: Towards better understanding and management of Propionibacterium acnes in cases of prosthetic valve endocarditis

We would like to thank Dr Mestrovic and colleagues for their comments and kind words regarding our paper on prosthetic valve endocarditis (PVE) caused by Propionibacterium acnes (P. acnes). We would like to take this opportunity to further clarify the issues raised in this commentary. We fully agree with Dr Mestrovic and colleagues that the diagnosis of PVE due to P. acnes can be challenging in the clinical setting and would like to take this opportunity to provide further information on our microbiological techniques as requested. Bactec aerobic and anaerobic culture bottles were used. The material was incubated for 14 days at 35 degrees Celsius in the Bactec FX blood culture system (Becton Dickinson). Cardiac valve tissue was incubated 14 days at 35 degrees Celsius on, amongst others, Brucella 5% blood agar anaerobic plates. P. acnes was identified on the basis of colony morphology and identification was confirmed by mass spectrometry (Maldi Biotyper, Bruker). Concerning the question on neurological complications due to P. acnes. As shown in table 2 of our paper 2 patients presented with neurological deficit. These episodes were transient. The percentage of patients is comparable to the generic cohort of patients presenting with PVE in our institute and did not constitute a higher risk of mortality is this small series.
The PCR technique can indeed be very valuable to confirm the diagnosis, as Dr Mestrovic argues, and can be performed in difficult cases. However, the technique is costly and is not standard of care in most countries. We would advocate proper culturing with a prolonged incubation time in patients with the likelihood of P. acnes PVE.
Using the current literature and our own experience we would not advocate longer terms of antibiotic treatment in patients with P acnes PVE or a conservative approach without surgery. Six weeks should be sufficient. If a patient is inoperable, the idea of suppression therapy with prolonged antibiotics could be entertained. In our series we used a conservative approach in one patient. This patient did not show a dehiscence of his mechanical valve. This seems to be the pivotal point for a potential successful treatment of PVE due to P. acnes without surgery.
Lastly, the importance of more studies, as also argued by Mestrovic, is there. In our article we warn about the possible underdiagnoses of P. acnes PVE due to a large differences in incubation durations and the wrongfully presumed innocence of P. acnes