Propionibacterium acnes as an etiological agent of arthroplastic and osteosynthetic infections--two cases with specific clinical presentation including formation of draining fistulae

Genomic characterization and clinical evaluation of prosthetic joint infections caused by Cutibacterium acnes

Cutibacterium acnes is a major skin commensal that may act as an opportunistic pathogen. It is difficult to interpret findings of C. acnes in tissue cultures obtained during arthroplasty revision surgery, since they may represent true infection or contamination. This study investigated whether C. acnes obtained from prosthetic joint infections (PJIs) were related and shared common genomic traits that might correlate with clinical courses and patient outcomes. C. acnes isolates from revision surgery of patients with PJIs of the hip, shoulder, and knee were characterized using molecular methods to determine the sequence type (ST) and the presence of possible virulence determinants (Christie-Atkins-Munch-Peterson factors, dermatan sulfate-binding adhesion 1, hyaluronidase lyase, and linear plasmid). A standardized review of the patients' medical charts was performed. The study included 37 patients with C. acnes culture-positive tissue samples where multiple isolates of C. acnes belonged to the same ST. Most of the isolates belonged to phylotype IA1. Phylogenetic analysis of virulence determinants revealed no shared pattern among PJI isolates. Seven patients had a polymicrobial infection. Exchange revision was performed in 70% of the patients, and >50% of all patients received antibiotic treatment for ≥3 months. Failure was noted in seven patients. No specific ST or any identifiable unique feature among virulence determinants were found among C. acnes isolated from PJIs of hips and shoulders. The majority of patients had low inflammatory markers and were treated successfully, even polymicrobial infections. However, failure was more common among shoulder infections compared with hip infections.

IMPORTANCE

Prosthetic joint infection (PJI) is a rare complication after arthroplasty surgery. The infection seldom resolves without a combination of both surgical and antibiotic treatment and can cause significant suffering among affected patients. Cutibacterium acnes is a common skin bacterium that is most often found in shoulder PJIs but can also infect other prostheses. In this study, we conducted a review of patients with previously verified PJIs involving C. acnes in hip or shoulder prostheses, along with a genomic analysis of the bacteria causing the infections. The majority of patients had successful outcomes. We did not identify any specific phylogenetic lineage or specific molecular signature of virulence factors among these PJI-associated C. acnes isolates that seemed to be associated with increased potential to cause infection among this species. This indicates that C. acnes isolated from PJIs originates from the patients' own skin microbiome and is inoculated during the arthroplasty surgery.

Characterization of a Propionibacterium acnes Surface Protein as a Fibrinogen-Binding Protein

Propionibacterium acnes (P. acnes) is a major skin-associated bacterium that was long considered commensal, until several studies revealed it to be an opportunistic pathogen. We investigated the ability of P. acnes surface proteins to recognize ECM proteins and showed that a 58 kDa P. acnes surface protein was specifically recognized by human fibrinogen (hFg). The 58 kDa protein was further characterized by two-dimensional (2-D) electrophoresis and MALDI-ToF as a P. acnes host cell-surface attachment protein, PA25957, recognizing dermatan sulfate (DsA1). This protein sequence contains 432 amino acids with the presence of three structurally different domains: an N-terminal signal peptide, a C-terminal LPXTG motif, and a PT repeat region. DsA1 is mostly produced during stationary phase. It appears to be highly glycosylated, containing GalNAc residues. Purified DsA1 strongly recognizes the Aα and Bβ subunits of hFg, and specific enzymatic deglycosylation of hFg demonstrated the involvement of the protein backbone in the recognition process. The Bβ subunit of hFg was cloned in four peptide fractions (Fg1-Fg4). The N-terminal Fg1 peptide of hFg was recognized by DsA1, and priming DsA1 with Fg1 inhibited DsA1/hFg recognition. We describe here for the first time, the characterization of a P. acnes surface glycoprotein recognizing human fibrinogen.

Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen

Propionibacterium acnes is known primarily as a skin commensal. However, it can present as an opportunistic pathogen via bacterial seeding to cause invasive infections such as implant-associated infections. These infections have gained more attention due to improved diagnostic procedures, such as sonication of explanted foreign materials and prolonged cultivation time of up to 14 days for periprosthetic biopsy specimens, and improved molecular methods, such as broad-range 16S rRNA gene PCR. Implant-associated infections caused by P. acnes are most often described for shoulder prosthetic joint infections as well as cerebrovascular shunt infections, fibrosis of breast implants, and infections of cardiovascular devices. P. acnes causes disease through a number of virulence factors, such as biofilm formation. P. acnes is highly susceptible to a wide range of antibiotics, including beta-lactams, quinolones, clindamycin, and rifampin, although resistance to clindamycin is increasing. Treatment requires a combination of surgery and a prolonged antibiotic treatment regimen to successfully eliminate the remaining bacteria. Most authors suggest a course of 3 to 6 months of antibiotic treatment, including 2 to 6 weeks of intravenous treatment with a beta-lactam. While recently reported data showed a good efficacy of rifampin against P. acnes biofilms, prospective, randomized, controlled studies are needed to confirm evidence for combination treatment with rifampin, as has been performed for staphylococcal implant-associated infections.

Physical stress and bacterial colonization

Bacterial surface colonizers are subject to a variety of physical stresses. During the colonization of human epithelia such as on the skin or the intestinal mucosa, bacteria mainly have to withstand the mechanical stress of being removed by fluid flow, scraping, or epithelial turnover. To that end, they express a series of molecules to establish firm attachment to the epithelial surface, such as fibrillar protrusions (pili) and surface-anchored proteins that bind to human matrix proteins. In addition, some bacteria--in particular gut and urinary tract pathogens--use internalization by epithelial cells and other methods such as directed inhibition of epithelial turnover to ascertain continued association with the epithelial layer. Furthermore, many bacteria produce multilayered agglomerations called biofilms with a sticky extracellular matrix, providing additional protection from removal. This review will give an overview over the mechanisms human bacterial colonizers have to withstand physical stresses with a focus on bacterial adhesion.

Septic nonunions of lower limb long bones: don't neglect Propionibacterium acnes!

We report 3 clinical cases of septic nonunions of lower limb long bones in which the pathogenicity of Propionibacterium acnes was retained after several weeks of poor outcome. The patients had fractures that were treated by internal fixation, without initially suspected infection. The diagnosis of delayed union coincided with the onset of treatment. Support was performed in 2 steps, allowing for the collection of several deep samples that were referred for microbiological analysis. Molecular techniques for microbiological investigation were performed on perioperative samples and were not contributive. The detection of P acnes, which was identified after several days of incubation, prompted us to consider the role of this bacterium. The presence of P acnes is regularly interpreted as contamination of samples during collection or handling in the laboratory. A multidisciplinary decision to make the diagnosis of surgical site infection with P acnes and specific antibiotic treatment for several months led to consolidation in all the patients. The ability of bacteria of the genus Propionibacterium to cause insidious surgical site infections should not be underestimated, and more extensive sample incubation is essential to diagnose such infections.

Complete Genome Sequence of a Propionibacterium acnes Isolate from a Sarcoidosis Patient

Propionibacterium acnes is a human skin commensal that resides preferentially within sebaceous follicles and is the only microorganism that has been isolated from sarcoid lesions. We report the complete genome sequence of P. acnes, which was isolated from a Japanese patient with sarcoidosis.

Multilocus sequence typing and repetitive-sequence-based PCR (DiversiLab) for molecular epidemiological characterization of Propionibacterium acnes isolates of heterogeneous origin

Propionibacterium acnes is a gram-positive bacillus predominantly found on the skin. Although it is considered an opportunistic pathogen it is also been associated with severe infections. Some specific P. acnes subtypes are hypothesized to be more prone to cause infection than others. Thus, the aim of the present study was to investigate the ability to discriminate between P. acnes isolates of a refined multilocus sequence typing (MLST) method and a genotyping method, DiversiLab, based on repetitive-sequence-PCR technology. The MLST and DiversiLab analysis were performed on 29 P. acnes isolates of diverse origins; orthopedic implant infections, deep infections following cardiothoracic surgery, skin, and isolates from perioperative tissue samples from prostate cancer. Subtyping was based on recA, tly, and Tc12S sequences. The MLST analysis identified 23 sequence types and displayed a superior ability to discriminate P. acnes isolates compared to DiversiLab and the subtyping. The highest discriminatory index was found when using seven genes. DiversiLab was better able to differentiate the isolates compared to the MLST clonal complexes of sequence types. Our results suggest that DiversiLab can be useful as a rapid typing tool for initial discrimination of P. acnes isolates. When better discrimination is required, such as for investigations of the heterogeneity of P. acnes isolates and its involvement in different pathogenic processes, the present MLST protocol is valuable.

Antibiotic susceptibility in prostate-derived Propionibacterium acnes isolates

The aim of this study was to determine antibiotic susceptibility of Propionibacterium acnes isolates from prostate. Prostate-derived P. acnes isolates (n = 24, Umeå & Örebro, Sweden, 2007-2010) and a panel of control strains (n = 25, Sweden) collected from skin and deep infections were assessed for resistance to penicillin G, piperacillin-tazobactam, imipenem, gentamicin, azithromycin, erythromycin, vancomycin, ciprofloxacin, moxifloxacin, tetracycline, tigecycline, fusidic acid, clindamycin, rifampicin, linezolid, daptomycin, trimethoprim-sulfamethoxazole, and metronidazole. In addition, the isolates were tested for inducible clindamycin resistance. All prostate derived P. acnes isolates displayed wild-type distribution of MIC-values, without evidence of acquired resistance. In the reference panel, 5 of 25 isolates had acquired macrolide resistance with cross-resistance to azithromycin, clindamycin, and erythromycin. In addition, one of these isolates was resistant to tetracycline.

Propionibacterium acnes: infection beyond the skin

Propionibacterium acnes is a Gram-positive bacterium that forms part of the normal flora of the skin, oral cavity, large intestine, the conjunctiva and the external ear canal. Although primarily recognized for its role in acne, P. acnes is an opportunistic pathogen, causing a range of postoperative and device-related infections. These include infections of the bones and joints, mouth, eye and brain. Device-related infections include those of joint prostheses, shunts and prosthetic heart valves. P. acnes may play a role in other conditions, including inflammation of the prostate leading to cancer, SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) syndrome, sarcoidosis and sciatica. If an active role in these conditions is established there are major implications for diagnosis, treatment and protection. Genome sequencing of the organism has provided an insight into the pathogenic potential and virulence of P. acnes.

Role of rifampin against Propionibacterium acnes biofilm in vitro and in an experimental foreign-body infection model

Propionibacterium acnes is an important cause of orthopedic-implant-associated infections, for which the optimal treatment has not yet been determined. We investigated the activity of rifampin, alone and in combination, against planktonic and biofilm P. acnes in vitro and in a foreign-body infection model. The MIC and the minimal bactericidal concentration (MBC) were 0.007 and 4 μg/ml for rifampin, 1 and 4 μg/ml for daptomycin, 1 and 8 μg/ml for vancomycin, 1 and 2 μg/ml for levofloxacin, 0.03 and 16 μg/ml for penicillin G, 0.125 and 512 μg/ml for clindamycin, and 0.25 and 32 μg/ml for ceftriaxone. The P. acnes minimal biofilm eradication concentration (MBEC) was 16 μg/ml for rifampin; 32 μg/ml for penicillin G; 64 μg/ml for daptomycin and ceftriaxone; and ≥128 μg/ml for levofloxacin, vancomycin, and clindamycin. In the animal model, implants were infected by injection of 10⁹ CFU P. acnes in cages. Antimicrobial activity on P. acnes was investigated in the cage fluid (planktonic form) and on explanted cages (biofilm form). The cure rates were 4% for daptomycin, 17% for vancomycin, 0% for levofloxacin, and 36% for rifampin. Rifampin cured 63% of the infected cages in combination with daptomycin, 46% with vancomycin, and 25% with levofloxacin. While all tested antimicrobials showed good activity against planktonic P. acnes, for eradication of biofilms, rifampin was needed. In combination with rifampin, daptomycin showed higher cure rates than with vancomycin in this foreign-body infection model.

Granulomatous Propionibacterium acnes infection after trauma surgery

We report here a rare case of infection caused by Propionibacterium acnes following trauma surgery: a 36-year-old male, accident victim was admitted to the hospital because of polytrauma. He underwent a long-drawn-out surgical intervention and after a free-muscle transfer using the rectus femoris muscle, signs of inflammation were detected in the affected area. Microbiological examination of the wound revealed the presence of P. acnes as the only etiological agent of this infection. Adequate antibiotic treatment with penicillin had been started right after the positive microbiological result. Our data confirm the pathogenic potential of P. acnes in late post-surgical infections, and suggest a proper therapeutic approach with intravenous antibiotics and surgical removal of the infected tissue.

Comparative genomics and transcriptomics of Propionibacterium acnes

The anaerobic gram-positive bacterium Propionibacterium acnes is a human skin commensal that is occasionally associated with inflammatory diseases. Recent work has indicated that evolutionary distinct lineages of P. acnes play etiologic roles in disease while others are associated with maintenance of skin homeostasis. To shed light on the molecular basis for differential strain properties, we carried out genomic and transcriptomic analysis of distinct P. acnes strains. We sequenced the genome of the P. acnes strain 266, a type I-1a strain. Comparative genome analysis of strain 266 and four other P. acnes strains revealed that overall genome plasticity is relatively low; however, a number of island-like genomic regions, encoding a variety of putative virulence-associated and fitness traits differ between phylotypes, as judged from PCR analysis of a collection of P. acnes strains. Comparative transcriptome analysis of strains KPA171202 (type I-2) and 266 during exponential growth revealed inter-strain differences in gene expression of transport systems and metabolic pathways. In addition, transcript levels of genes encoding possible virulence factors such as dermatan-sulphate adhesin, polyunsaturated fatty acid isomerase, iron acquisition protein HtaA and lipase GehA were upregulated in strain 266. We investigated differential gene expression during exponential and stationary growth phases. Genes encoding components of the energy-conserving respiratory chain as well as secreted and virulence-associated factors were transcribed during the exponential phase, while the stationary growth phase was characterized by upregulation of genes involved in stress responses and amino acid metabolism. Our data highlight the genomic basis for strain diversity and identify, for the first time, the actively transcribed part of the genome, underlining the important role growth status plays in the inflammation-inducing activity of P. acnes. We argue that the disease-causing potential of different P. acnes strains is not only determined by the phylotype-specific genome content but also by variable gene expression.

Passive immunoprotection targeting a secreted CAMP factor of Propionibacterium acnes as a novel immunotherapeutic for acne vulgaris

Propionibacterium acnes (P. acnes) bacteria play a key role in the pathogenesis of acne vulgaris. Although our previous studies have demonstrated that vaccines targeting a surface sialidase or bacterial particles exhibit a preventive effect against P. acnes, the lack of therapeutic activities and incapability of neutralizing secretory virulence factors motivate us to generate novel immunotherapeutics. In this study, we develop an immunotherapeutic antibody to secretory Christie-Atkins-Munch-Peterson (CAMP) factor of P. acnes. Via agroinfiltration, P. acnes CAMP factor was encapsulated into the leaves of radishes. ICR mice intranasally immunized with whole leaves expressing CAMP factor successfully produced neutralizing antibodies that efficiently attenuated P. acnes-induced ear swelling and production of macrophage-inflammatory protein-2. Passive neutralization of CAMP factor enhanced immunity to eradicate P. acnes at the infection site without influencing bacterial growth elsewhere. We propose that CAMP factor is a novel therapeutic target for the treatment of various P. acnes-associated diseases and highlight the concept of neutralizing P. acnes virulence without disturbing the bacterial commensalism in human microbiome.