Susceptibility and molecular characterisation of Cutibacterium acnes from patients with bone and joint infection samples in South Africa

Abstract

Background: Cutibacterium acnes is a commensal on healthy human skin but can cause infections such as biofilm-associated prostheses/hardware infections. There is no published South African data on the susceptibility and phylogeny of C. acnes causing bone and joint infection. Empiric treatment, guided mainly by international data, shows high clindamycin resistance in C. acnes. Clindamycin would be a helpful oral treatment option due to its bioavailability and good bone penetration. The study aims to assess the susceptibility profiles of C. acnes isolates sent to the laboratory from prosthetic joint infection (PJI) patients in South Africa to guide antimicrobial therapy. The molecular characterisation seeks to assess the genetic similarity between the isolated strains and to determine which phylotypes predominate in bone and joint infections.

Methods: A retrospective analysis of antibiotic susceptibility profiles was performed for all intraoperative, periprosthetic samples from patients with PJI, fracture-related infection and post-rotator cuff repair sent routinely to Lancet Laboratories in Cape Town from January 2022 to May 2024. Only sample sets where C. acnes was isolated on two or more samples were analysed. One organism for each set of samples was used for the phylogenetic analysis. Single Locus Sequence Typing (SLST) was used to perform phylotyping on the viable C. acnes isolates.

Results: Thirty-one C. acnes isolates (one per set of samples) were identified. There was 100% (31/31) susceptibility to vancomycin, piperacillin-tazobactam, and penicillin; 81% (25/31) susceptibility to meropenem; and 87% (27/31) susceptibility to clindamycin. Of the 12 typed strains, all showed a high degree of genetic similarity.

Conclusion: These data show 100% susceptibility to the intravenous agents vancomycin, penicillin and piperacillin-tazobactam, and a high degree of susceptibility to clindamycin, which can be taken orally. This finding indicates that local susceptibility data is essential in guiding treatment strategies for South African populations. The local phylogeny indicates that strains share a common evolutionary history.

Level of evidence: 4