Monday, August 7, 2017

Propionibacterium - not only acnes, not only in the shoulder

Propionibacterium avidum – a virulent pathogen causing hip periprosthetic joint infection

These authors report four hip prosthetic joint infections caused by P. avidum in one orthopedic center in 2015. They also characterized the hemolytic and biofilm-producing capacity of the four clinical P. avidum strains and investigated their phylogenetic relationships by whole genome sequencing. On searching their records from 1997 to 2015 they  retrospectively identified 13 P. avidum PJIs, with the majority being hip-related infections (n=11).

Preoperative synovial fluid cultures were P. avidum positive in 63.6% of cases. Six out of 12 patients (50%) with available case histories were treated with an exchange of the prosthesis. In all but one of the six patients treated with debridement-retention of the prosthesis, treatment failed thus requiring a two-stage revision. 

The isolated P. avidum strains showed a more pronounced hemolytic activity, but a similar biofilm-forming ability when compared to P. acnes.

 Whole genome sequencing identified two phylogenetic clusters highly related to P. avidum PJI strains isolated in Sweden.

Comment: As we become more accurate and precise in our characterization of Propionibacterium recovered from prosthetic joint infections, it is important to recognize that P. Acnes is not the only species of clinical importance as is pointed out in this article and in these links: Propionibacterium – What we think we know today and Genome Sequence of a Novel Species, Propionibacterium humerusii.  As is true for other bacterial species, it is reasonable to expect that these other species (P. avidum, P. granulosum, P. humerusii, and perhaps others) may have different clinical features and different antibiotic sensitivities from P. acnes. We need to ask our laboratories to put forth the additional effort to speciate Propionibacterium, rather than reporting them all as "P. acnes".  As shoulder surgeons, we need to share these insights with our hip, knee and spine colleagues in that they are likely to encounter these organisms as well.

The retrospective nature of this study is very likely to underestimate the incidence of Propionibacterium in the arthroplasty revisions because the culture protocol used for these patients is not explained. Specifically, we do not know which cases were cultured, how many specimens were submitted for culture, what culture media were used, and how long the cultures were observed. It is known that unless 5 deep specimens are cultured on three different media and observed for 3 weeks, there is a substantial risk of overlooking Propionibacterium in the wound (see Origin of propionibacterium in surgical wounds and evidence-based approach for culturing propionibacterium from surgical sites).

This study does not present the data on revised joints that were culture positive for P. acnes or other Propionibacterium species during the same time interval.

Finally, this study points out that complete prothesis exchange may be necessary to resolve Propionibacterium infections.

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