Propionibacterium acnes Susceptibility and Correlation with Hemolytic Phenotype

Abstract

Background: Many studies have noted an increase in the number of recognized cases of invasive infections due to Propionibacterium acnes, especially after shoulder replacement surgery. The increase in the number of recognized cases of P. acnes, a nonspore-forming, anaerobic, Gram-positive organism, appears due to both an increase in the number of shoulder operations being performed and more specimens being sent for anaerobic cultures. Nevertheless, the optimal surgical and antibiotic management of P. acnes remains controversial.

Methods: We tested the susceptibility of 106 P. acnes strains from sterile body sites collected at the Erie County Medical Center between 2012 and 2015, using Etest gradient antibiotic strips.

Results: P. acnes is very susceptible to the penicillins and the first-generation cephalosporins. We noted an association between hemolytic phenotype on Brucella Blood Agar and clindamycin resistance.

Conclusions: Antimicrobial susceptibility testing of P. acnes should no longer just be confined to the research laboratory but expanded and incorporated into routine microbiological evaluation of P. acnes. This would improve patient care as well as help clarify the relationship between hemolysis and clindamycin resistance.

Keywords: clindamycin; hemolysin; penicillin G; sarcoidosis.

Conflict of interest statement

TRD discloses a research grant and consulting fees from Zimmer-Biomet, outside the work presented here. Other authors disclose no potential conflicts of interest.

Figures

Figure 1

Distribution of the sources of the P. acnes isolates according to anatomical site.

Figure 2

Histogram of the distribution of MICs of 106 P. acnes strains to clindamycin. Inset graph shows a subset of strains with MICs <14 µg/mL.

Figure 3

Hemolysis and antibiotic-induced hemolysis among P. acnes strains on Brucella Blood Agar. (A) Comparison of a hemolytic strain and a nonhemolytic P. acnes strain on the same Petri dish. (B) Appearance of strains showing weak antibiotic-induced hemolysis and strong antibiotic-induced hemolysis in P. acnes. (C) Absence of antibiotic-induced hemolysis surrounding a clindamycin Etest strip, which is photographed using transmitted light on a light box. (D) Absence of antibiotic-induced hemolysis surrounding a ciprofloxacin E-test strip, which is photographed using reflected light.

Figure 4

Lack of effect of induced hemolysis on clindamycin susceptibility in P. acnes. Aerolysin, a potent hemolysin from Aeromonas hydrophila bacteria, was used to induce hemolysis on agars not permissive for P. acnes hemolysis. (A) P. acnes strain 77 on TSA + 5% sheep’s blood, testing the clindamycin MIC in the absence (left) or presence (right) of aerolysin. (B) The same plate photographed via transmitted light on a light box shows the hemolysis induced by the aerolysin. Bacterial growth is not well seen in transmitted light conditions in (B). (C) Lack of effect of aerolysin on the clindamycin MIC of a moderately resistant P. acnes strain. Arrows indicate the MIC of 6 µg/mL.