Monday, March 12, 2018

Propionibacterium - are hemolytic strains more virulent?

Hemolytic strains of Propionibacterium acnes do not demonstrate greater pathogenicity in periprosthetic shoulder infections

Certain strains of Propionibacterium result in hemolysis when streaked on a blood agar plate as shown in "A" below in contrast to "B" which does not show hemolysis.

Some authors have suggested that hemolysis is associated with increased pathogenicity of certain strains of Propionibacterium

These authors studied 39 patients with at least 1 positive culture for P acnes at the time of revision shoulder arthroplasty who also had testing of the Propionibacterium for hemolysis. 20 of the isolated strains showed hemolytic activity and 19 did not. 

The presence of hemolysis was not significantly associated with greater clinical evidence of infection. The hemolytic and nonhemolytic groups showed no difference regarding preoperative serum erythrocyte sedimentation rate and/or C-reactive protein level (P = .70), number of positive cultures (P = .395), time to positive culture (P = .302), and presence of positive frozen section findings (P = .501). Postoperatively, clindamycin resistance, shoulder function, and the rate of reoperation were not significantly different between the hemolytic and nonhemolytic groups.

These authors point out that a prior study by Nodzo et al in 2014 demonstrated significantly elevated
CRP levels in hemolysis-positive patients.  More recently, this group expanded their analysis with 31 patients evaluated for hemolysis. In that study by Boyle et al 2016 showed significantly elevated ESR and CRP levels, as well as a significantly greater percentage (31% vs 0%) of antibiotic resistance, in cases with hemolysis-positive Propionibacterium cultures.

Comment: At this point it is difficult to be sure whether or not hemolytic strains are more virulent than non-hemolytic strains of Propionibacterium.  It is clear, however, that all strains of Propionibacterium are not the same as revealed by the hemolytic phenotype as well as the Clindamycin-resistant phenotype. How these differences affect the diagnosis, clinical course and management of Propionibacterium in revision arthroplasty remains to be seen.

Interested readers may be interested in these two articles:

Genetic profiles of Propionibacterium acnes and identification of a unique transposon with novel insertion sequences in sarcoid and non-sarcoid isolates  which identified two hemolytic-associated genes (camp 5 and tly) and

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