Are Cutibacterium acnes present at the end of primary shoulder prosthetic surgeries responsible for infection? Prospective study.

The purpose of this study was to investigate if the C. acnes present at the end of a primary shoulder arthroplasty could be responsible for shoulder arthroplasty infection. Prospective study includes patients undergoing primary shoulder arthroplasty from January 2015 until December 2018. From all the patients included, 5 to 12 tissue samples were obtained and were specifically cultured to detect the presence of C. acnes. DNA was extracted from the C acnes isolated colonies and Whole Genome Sequencing (WGS) analysis was done. A cohort of 156 patients was finally included. In twenty-seven patients, the C. acnes was present at the end of the primary surgery. Two of these patients developed a C. acnes periprosthetic shoulder infection at 6 and 4 months after the primary surgery. WGS of C. acnes isolated colonies showed that all the revision-surgery isolates clustered near to the corresponding primary-surgery isolates compared to the other independent bacterial colonies. (99.89% of similarity). C. acnes present at the end of the primary surgery can be the cause of early or delayed periprosthetic joint infections in shoulder arthroplasty.

Lactobacillus rhamnosus GG modifies the metabolome of pathobionts in gnotobiotic mice.

BACKGROUND: Lactobacillus rhamnosus GG (LGG) is the most widely used probiotic, but the mechanisms underlying its beneficial effects remain unresolved. Previous studies typically inoculated LGG in hosts with established gut microbiota, limiting the understanding of specific impacts of LGG on host due to numerous interactions among LGG, commensal microbes, and the host. There has been a scarcity of studies that used gnotobiotic animals to elucidate LGG-host interaction, in particular for gaining specific insights about how it modifies the metabolome. To evaluate whether LGG affects the metabolite output of pathobionts, we inoculated with LGG gnotobiotic mice containing Propionibacterium acnes, Turicibacter sanguinis, and Staphylococcus aureus (PTS). RESULTS: 16S rRNA sequencing of fecal samples by Ion Torrent and MinION platforms showed colonization of germ-free mice by PTS or by PTS plus LGG (LTS). Although the body weights and feeding rates of mice remained similar between PTS and LTS groups, co-associating LGG with PTS led to a pronounced reduction in abundance of P. acnes in the gut. Addition of LGG or its secretome inhibited P. acnes growth in culture. After optimizing procedures for fecal metabolite extraction and metabolomic liquid chromatography-mass spectrometry analysis, unsupervised and supervised multivariate analyses revealed a distinct separation among fecal metabolites of PTS, LTS, and germ-free groups. Variables-important-in-projection scores showed that LGG colonization robustly diminished guanine, ornitihine, and sorbitol while significantly elevating acetylated amino acids, ribitol, indolelactic acid, and histamine. In addition, carnitine, betaine, and glutamate increased while thymidine, quinic acid and biotin were reduced in both PTS and LTS groups. Furthermore, LGG association reduced intestinal mucosal expression levels of inflammatory cytokines, such as IL-1α, IL-1ß and TNF-α. CONCLUSIONS: LGG co-association had a negative impact on colonization of P. acnes, and markedly altered the metabolic output and inflammatory response elicited by pathobionts.

Identifying and exploring biohydrogenating rumen bacteria with emphasis on pathways including trans-10 intermediates.

BACKGROUND: Bacteria involved in ruminal formation of trans-10 intermediates are unclear. Therefore, this study aimed at identifying rumen bacteria that produce trans-10 intermediates from 18-carbon unsaturated fatty acids. RESULTS: Pure cultures of 28 rumen bacterial species were incubated individually in the presence of 40 µg/mL 18:3n-3, 18:2n-6 or trans-11 18:1 under control or lactate-enriched (200 mM Na lactate) conditions for 24 h. Of the 28 strains, Cutibacterium acnes (formerly Propionibacterium acnes) was the only bacterium found to produce trans-10 intermediates from 18:3n-3 and 18:2n-6, irrespective of the growth condition. To further assess the potential importance of this species in the trans-11 to trans-10 shift, different biomass ratios of Butyrivibrio fibrisolvens (as a trans-11 producer) and C. acnes were incubated in different growth media (control, low pH and 22:6n-3 enriched media) containing 40 µg/mL 18:2n-6. Under control conditions, a trans-10 shift, defined in the current study as trans-10/trans-11 ≥ 0.9, occurred when the biomass of C. acnes represented between 90 and 98% of the inoculum. A low pH or addition of 22:6n-3 inhibited cis-9, trans-11 CLA and trans-10, cis-12 CLA formation by B. fibrisolvens and C. acnes, respectively, whereby C. acnes seemed to be more tolerant. This resulted in a decreased biomass of C. acnes required at inoculation to induce a trans-10 shift to 50% (low pH) and 90% (22:6n-3 addition). CONCLUSIONS: Among the bacterial species studied,C. acnes was the only bacterium that have the metabolic ability to produce trans-10 intermediates from 18:3n-3 and 18:2n-6. Nevertheless, this experiment revealed that it is unlikely that C. acnes is the only or predominant species involved in the trans-11 to trans-10 shift in vivo.

PEG-8 Laurate Fermentation of Staphylococcus epidermidis Reduces the Required Dose of Clindamycin Against Cutibacterium acnes.

The probiotic activity of skin Staphylococcus epidermidis (S. epidermidis) bacteria can elicit diverse biological functions via the fermentation of various carbon sources. Here, we found that polyethylene glycol (PEG)-8 Laurate, a carbon-rich molecule, can selectively induce the fermentation of S. epidermidis, not Cutibacterium acnes (C. acnes), a bacterium associated with acne vulgaris. The PEG-8 Laurate fermentation of S. epidermidis remarkably diminished the growth of C. acnes and the C. acnes-induced production of pro-inflammatory macrophage-inflammatory protein 2 (MIP-2) cytokines in mice. Fermentation media enhanced the anti-C. acnes activity of a low dose (0.1%) clindamycin, a prescription antibiotic commonly used to treat acne vulgaris, in terms of the suppression of C. acnes colonization and MIP-2 production. Furthermore, PEG-8 Laurate fermentation of S. epidermidis boosted the activity of 0.1% clindamycin to reduce the sizes of C. acnes colonies. Our results demonstrated, for the first time, that the PEG-8 Laurate fermentation of S. epidermidis displayed the adjuvant effect on promoting the efficacy of low-dose clindamycin against C. acnes. Targeting C. acnes by lowering the required doses of antibiotics may avoid the risk of creating drug-resistant C. acnes and maintain the bacterial homeostasis in the skin microbiome, leading to a novel modality for the antibiotic treatment of acne vulgaris.

Suppression of Propionibacterium acnes-Induced Skin Inflammation by Laurus nobilis Extract and Its Major Constituent Eucalyptol.

Acne is an inflammatory skin disorder in puberty with symptoms including papules, folliculitis, and nodules. Propionibacterium acnes (P. acnes) is the main anaerobic bacteria that cause acne. It is known to proliferate within sebum-blocked skin hair follicles. P. acnes activates monocytic cell immune responses to induce the expression of proinflammatory cytokines. Although the anti-inflammatory function of the Laurus nobilis (L. nobilis) extract (LNE) on several immunological disorders have been reported, the effect of LNE in P. acnes-mediated skin inflammation has not yet been explored. In the present study, we examined the ability of the LNE to modulate the P. acnes-induced inflammatory signaling pathway, and evaluated its mechanism. LNE significantly suppressed the expression of P. acnes-mediated proinflammatory cytokines, such as IL-1ß, IL-6, and NLRP3. We also found that LNE inhibited the inflammatory transcription factor NF-κB in response to P. acnes. In addition, eucalyptol, which is the main constituent of LNE, consistently inhibited P. acnes-induced inflammatory signaling pathways. Moreover, LNE significantly ameliorated P. acnes-induced inflammation in a mouse model of acne. We suggest for the first time that LNE hold therapeutic value for the improvement of P. acnes-induced skin inflammation.

Rational Design and Synthesis of Modified Teixobactin Analogues: In Vitro Antibacterial Activity against Staphylococcus aureus, Propionibacterium acnes and Pseudomonas aeruginosa.

Teixobactin, a recently discovered depsipeptide that binds to bacterial lipid II and lipid III, provides a promising molecular scaffold for the design of new antimicrobials. Herein, we describe the synthesis and antimicrobial evaluation of systematically modified teixobactin analogues. The replacement of the Ile11 residue with aliphatic isosteres, the modification of the guanidino group at residue 10 and the introduction of a rigidifying residue, that is, dehydroamino acid, into the macrocyclic ring generated useful structure-activity information. Extensive antimicrobial susceptibility assessment against a panel of clinically relevant Staphylococcus aureus and Propionibacterium acnes strains led to the identification of the new lead compound, [Arg(Me)10 ,Nle11 ]teixobactin, with an excellent bactericidal activity (minimum inhibitory concentration (MIC)=2-4 µg mL-1 ). Significantly, the antimicrobial activity of several of the teixobactin analogues against the pathogenic Gram-negative Pseudomonas aeruginosa was "restored" when combined with the sub-MIC concentration of the outer membrane-disruptive antibiotic colistin. The antimicrobial effectiveness of a [Tfn10 ,Nle11 ]teixobactin (32 µg mL-1 )-colistin (2 µg mL-1 ; 0.5×MIC) combination against P. aeruginosa PAO1 reveals, for the first time, an alternative therapeutic option in the treatment of Gram-negative infections.

Solar UV radiation and microbial life in the atmosphere.

Many microorganisms are alive while suspended in the atmosphere, and some seem to be metabolically active during their time there. One of the most important factors threatening their life and activity is solar ultraviolet (UV) radiation. Quantitative understanding of the spatial and temporal survival patterns in the atmosphere, and of the ultimate deposition of microbes to the surface, is limited by a number factors some of which are discussed here. These include consideration of appropriate spectral sensitivity functions for biological damage (e.g. inactivation), and the estimation of UV radiation impingent on a microorganism suspended in the atmosphere. We show that for several bacteria (E. coli, S. typhimurium, and P. acnes) the inactivation rates correlate well with irradiances weighted by the DNA damage spectrum in the UV-B spectral range, but when these organisms show significant UV-A (or visible) sensitivities, the correlations become clearly non-linear. The existence of these correlations enables the use of a single spectrum (here DNA damage) as a proxy for sensitivity spectra of other biological effects, but with some caution when the correlations are strongly non-linear. The radiative quantity relevant to the UV exposure of a suspended particle is the fluence rate at an altitude above ground, while down-welling irradiance at ground-level is the quantity most commonly measured or estimated in satellite-derived climatologies. Using a radiative transfer model that computes both quantities, we developed a simple parameterization to exploit the much larger irradiance data bases to estimate fluence rates, and present the first fluence-rate based climatology of DNA-damaging UV radiation in the atmosphere. The estimation of fluence rates in the presence of clouds remains a particularly challenging problem. Here we note that both reductions and enhancements in the UV radiation field are possible, depending mainly on cloud optical geometry and prevailing solar zenith angles. These complex effects need to be included in model simulations of the atmospheric life cycle of the organisms.

Propionibacterium acnes Abundance Correlates Inversely with Staphylococcus aureus: Data from Atopic Dermatitis Skin Microbiome.

The microbiome may influence disease severity in atopic dermatitis. The skin of atopic dermatitis patients and healthy individuals was sampled in a standardized manner and the microbial composition analysed using next-generation sequencing. Optical density measurements were used to investigate bacterial growth under defined conditions in vitro. Lesional skin from patients with atopic dermatitis had a higher abundance of Staphylococcus aureus and reduced quantities of Propionibacterium acnes and Lawsonella clevelandensis compared with non-lesional skin. The abundance of P. acnes correlated negatively with that of S. aureus (ρ= -0.6501, p < 0.0001). Fermentation products of P. acnes inhibited the growth of S. aureus and S. epidermidis. Serum from patients with atopic dermatitis inhibited the growth of S. aureus to a greater extent than did serum from healthy individuals. These results suggest that selective modification of the skin microbiome could potentially be used as a therapeutic strategy in atopic dermatitis.

In vitro evaluation of antagonism, modulation of cytokines and extracellular matrix proteins by Bifidobacterium strains.

A healthy skin provides a protective barrier against pathogenic micro-organisms. Recent studies have shown that probiotics, as those of Bifidobacterium genus, could act beneficially in dermatology, both when ingested and by topical use. In the present study, we evaluated by in vitro antagonism assays and using two skin cell lines the potential of four strains of Bifidobacterium spp. Among the four bifidobacteria, Bifidobacterium longum 51A was the only one able to inhibit the growth of the eight pathogenic indicators tested. Production of some cytokines and extracellular matrix proteins was determined when ccc or inactivated cells of the bifidobacteria were incubated with keratinocyte and/or fibroblast cell cultures. Significant results were observed only for IL-6, IL-8 and IL-18 production, and inactivated Bifidobacterium pseudolongum 1191A was the only one which significantly stimulated collagen production, whereas lumican was stimulated by treatments with live Bifidobacterium bifidum 1622A , B. longum 51A and B. pseudolongum 1191A . Highest adhesion and internalization capabilities were observed with B. bifidum 1622A and Bifidobacterium breve 1101A . Concluding, B. longum 51A was highlighted for its antagonistic capacity and B. bifidum 1622A and B. pseudolongum 1191A for stimulating the production of cytokines and proteins of the extracellular matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: The skin is the first line of defence against invasive micro-organisms, and its local microbiota provides additional protective functions based on antagonism against pathogenic micro-organisms and immunomodulation. Based on in vitro assays using Bifidobacterium spp. we demonstrated the antagonistic potential, as well as capacity in stimulating the production of cytokines and proteins of the extracellular matrix that these bacteria may exert on skin cells. This positive influence suggests the use of a consortium of these bifidobacteria in a topical product for dermatological treatments.

Alpha- and gamma-mangostins exhibit anti-acne activities via multiple mechanisms.

Objective: Acne is a chronic skin disease that involves four key pathogenic factors: excess sebum production, ductal epidermal hyperproliferation, Propionibacterium acnes (P. acnes) colonization, and skin inflammation. Mangostins are well-known for their anti-bacterial and anti-inflammatory effects, suggesting that mangostins may have therapeutic potential for acne. The present study aimed to explore the anti-acne effects of mangostins from the perspective of multiple pathogenic mechanisms of acne. Methods: The effects of α- and γ-mangostins on the growth of P. acnes and lipase activity were analyzed. Their effects on P. acnes-induced keratinocyte proliferation were examined by CCK-8. The expression of inflammatory genes and activation of NF-κB and MAPK signaling pathways were detected by quantitative real-time PCR and western blotting, respectively. Results: Alpha- and γ-mangostins not only inhibited the growth of P. acnes, but also reduced the proliferation of keratinocytes induced by heat-killed P. acnes. Furthermore, α- and γ-mangostins were able to suppress P. acnes-induced expression of pro-inflammatory cytokines, including TNF-α, IL-1ß, and IL-6 in keratinocytes by inhibiting the activation of NF-κB and MAPK signaling pathways. Discussion and conclusions: Mangostins appeared to possess multiple anti-acne activities, including the inhibition of P. acnes growth, regulation of keratinocytes proliferation, and attenuation of skin inflammatory reaction. Hence, mangostins might be developed into a potential therapeutic agent for the treatment of acne.

In-vitro evaluation of marine derived fungi against Cutibacterium acnes.

Cutibacterium acnes (or Propionibacterium acnes) is the main target for the prevention and medical treatment of acne vulgaris. The aim of this study was to evaluate the in vitro anti-C. acnes and anti-S. epidermidis properties of some marine fungi isolated from different Indian marine environments. Seventy fungal isolates were obtained from samples collected from the west coasts and Andaman Island, India. Methanol extracts of 35 isolates were screened for their antibacterial properties and 5 out of the 35 isolates displayed significant inhibition as compared with tetracycline. DNA was successfully extracted from these five fungal isolates and phylogenetic analysis was performed. The methanol extracts possessed antibacterial activity against C. acnes and S. epidermidis with MIC values ranged from 0.8 mg/mL to 1 mg/mL. SEM analysis revealed that the extract induces deleterious morphological changes in the bacterial cell membrane. This study has identified some fungi extracts with significant antibacterial activity. The extracts may have potential for development as an antibacterial agent in the treatment of acne vulgaris.

Kaempferia parviflora Extract as a Potential Anti-Acne Agent with Anti-Inflammatory, Sebostatic and Anti-Propionibacterium acnes Activity.

Kaempferia parviflora, referred to as black ginger, has traditionally been used as a health-promoting alternative medicine. In this study, we examined the anti-inflammatory, sebostatic, and anti-Propionibacterium acnes activities of K. parviflora extract. The extract significantly down-regulated the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), and pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) level. Moreover, the phosphorylation of IĸBα and nuclear factor-kappa B (NF-κB), and the enhanced nuclear translocation of NF-κB p65 in lipopolysaccharide-stimulated murine macrophage-like cell line (RAW 264.7) cells were markedly decreased by the extract. Notably, the main component of K. parviflora, 5,7-dimethoxyflavone, also modulated the expression of iNOS and NF-κB signal molecules in P. acnes-stimulated human keratinocyte (HaCaT) cells. Additionally, K. parviflora extract inhibited the lipogenesis of sebocytes, as evidenced by a reduced level of triglyceride and lipid accumulation in the sebocytes. The sebostatic effect was also confirmed by a reduced expression of peroxisome proliferation-activating receptors (PPAR-γ) and oil-red O staining in sebocytes. Taken together, this study suggests for the first time that K. parviflora extract could be developed as a potential natural anti-acne agent with anti-inflammatory, sebostatic, and anti-P. acnes activity.

Growth of Cutibacterium acnes is common on osteosynthesis material of the shoulder in patients without signs of infection.

Background and purpose - Cutibacterium acnes, formerly known as Propionibacterium acnes, is often isolated from deep tissues of the shoulder. It is recognized as an important causative agent of foreign-material associated infections. However, the incidence and significance of its detection in tissues from patients without clinical evidence for infection is unclear. We assessed the incidence of C. acnes colonization of osteosynthesis material in asymptomatic patients, and evaluated the short-term outcome in relation to the microbiological findings. Patients and methods - We microbiologically analyzed osteosynthesis material of 34 asymptomatic patients after surgery on the clavicle. Material obtained from 19 asymptomatic patients after osteosynthesis of the fibula served as a control group. Patients were clinically followed up for 3-24 months after removal of the osteosynthesis material. Results - Bacteria were recovered from devices in 29 of 34 patients from the clavicle group. 27 of 29 positive samples grew C. acnes. Isolation of C. acnes was more common in male than in female patients. No bacterial growth was observed on foreign material from patients in the fibula group. All patients remained asymptomatic at follow-up. Interpretation - Growth of C. acnes is common on osteosynthesis material of the shoulder, especially in males. Samples were positive irrespective of clinical signs of infection. Therefore, detection of C. acnes in this clinical setting is of questionable clinical significance. The high positivity rate in asymptomatic patients discourages routine sampling of material in cases without clinical evidence for infection.

In Vitro Activities of Pexiganan and 10 Comparator Antimicrobials against 502 Anaerobic Isolates Recovered from Skin and Skin Structure Infections.

Pexiganan, a cationic peptide, exhibited a broad range of anti-anaerobic antimicrobial activity. The MIC90s of studied isolates were as follows: Bacteroides fragilis, 16 µg/ml; other B. fragilis group spp., 4 µg/ml; Prevotella and Fusobacterium spp., 32 µg/ml; Porphyromonas spp., 64 µg/ml; Propionibacterium acnes, 4 µg/ml; Eggerthella lenta and Peptostreptococcus anaerobius, 32 µg/ml; other Gram-positive rods and cocci, 4 µg/ml; Clostridium perfringens, 128 µg/ml; and other clostridia, 256 µg/ml. Pexiganan cream shows potential as adjunctive therapy for skin and skin structure infections (SSSIs) involving anaerobes.

A Multifactorial Comparison of Ternary Combinations of Essential Oils in Topical Preparations to Current Antibiotic Prescription Therapies for the Control of Acne Vulgaris-Associated Bacteria.

Acne vulgaris, a chronic condition associated with overgrowth of Propionibacterium acnes and Staphylococcus epidermidis, is commonly treated with antibiotics. However, the emergence of antibiotic resistance has resulted in a need for alternative therapies. The aim of this study is to develop a topical preparation incorporating essential oils (EOs) for use against acne-associated bacteria and assess its efficacy against prescription therapies Dalacin T and Stiemycin. Antimicrobial screening of rosewood, clove bud and litsea EOs was conducted before interactions between binary and ternary combinations were determined against P. acnes and S. epidermidis (type and clinical isolates) using minimum inhibitory concentrations and fractional inhibitory concentrations. The EOs were characterised by both gas chromatography-mass spectrometry and nuclear magnetic resonance. A combination of 0.53 mg/mL litsea, 0.11 mg/mL rosewood and 0.11 mg/mL clove bud was formulated into herbal distillates and compared with Dalacin T and Stiemycin against antibiotic sensitive and resistant isolates (erythromycin). The distillate with EO had synergistic activity against P. acnes (7log10 reduction) and indifferent activity against S. epidermidis (6log10 reduction); antimicrobial activity was either significantly (p ≤ 0.05) more antimicrobial or equivalent to that of Dalacin T and Stiemycin. This formulation may serve as a valuable alternative for the control of acne vulgaris-associated bacteria. Copyright © 2017 John Wiley & Sons, Ltd.

Rhodomyrtone inhibits lipase production, biofilm formation, and disorganizes established biofilm in Propionibacterium acnes.

Virulence enzymes and biofilm a play crucial role in the pathogenesis of Propionibacterium acnes, a major causative agent of acne vulgaris. In the present study, the effects of rhodomyrtone, a pure compound identified from Rhodomyrtus tomentosa (Aiton) Hassk. leaves extract against enzyme production and biofilm formation production by 5 clinical isolates and a reference strain were evaluated. The degree of hydrolysis by both lipase and protease enzymes significantly decreased upon treatment with the compound at 0.125-0.25 µg/mL (p < 0.05). Lipolytic zones significantly reduced in all isolates while decrease in proteolytic activities was found only in 50% of the isolates. Rhodomyrtone at 1/16MIC and 1/8MIC caused significant reduction in biofilm formation of the clinical isolates (p < 0.05). Percentage viability of P. acnes within mature biofilm upon treated with the compound at 4MIC and 8MIC ranged between 40% and 85%. Pronounced properties of rhodomyrtone suggest a path towards developing a novel anti-acne agent.

Multiple Activities of Punica granatum Linne against Acne Vulgaris.

Acne is a common skin condition with sebum overproduction, hyperkeratosis, Propionibacterium acnes (P. acnes) and Staphylococcus aureus, and inflammation. Punica granatum (pomegranate) is well-known for its anti-inflammatory effects; however, few studies have discussed the anti-acne effects of pomegranate. In this study, we found that pomegranate extract (PG-E) significantly reduced P. acnes-induced edema in Wistar rat ears. Therefore, an evaluation platform using multiple pathogenic mechanisms of acne was established to explore the anti-acne effects of pomegranate. Results showed that PG-E inhibited bacterial growth and lipase activity. Through a bioguided-fractionation-isolation system, four hydrolysable tannins, punicalagin (1), punicalin (2), strictinin A (3), and granatin B (4), were isolated. Compounds 1 and 2 had greater anti-bacterial activities and anti-testosterone-induced HaCaT proliferative effects than the others. Compounds 1, 3, and 4 displayed lipase inhibitory effects. Compound 4 decreased cyclooxygenase-2 expression and downregulated prostaglandin E2 production in heat-killed P. acnes-treated RAW 246.7 cells. In conclusion, PG-E is abundant in hydrolysable tannins that display multiple anti-acne capacities, including anti-bacterial, anti-lipase, anti-keratinocyte proliferation, and anti-inflammatory actions. Hence, PG-E has great potential in the application of anti-acne and skin-care products, and punicalagin (1), the most effective component in PG-E, can be employed as a quality control marker.

Optimal Length of Cultivation Time for Isolation of Propionibacterium acnes in Suspected Bone and Joint Infections Is More than 7 Days.

Diagnosis of Propionibacterium acnes bone and joint infection is challenging due to the long cultivation time of up to 14 days. We retrospectively studied whether reducing the cultivation time to 7 days allows accurate diagnosis without losing sensitivity. We identified patients with at least one positive P. acnes sample between 2005 and 2015 and grouped them into "infection" and "no infection." An infection was defined when at least two samples from the same case were positive. Clinical and microbiological data, including time to positivity for different cultivation methods, were recorded. We found 70 cases of proven P. acnes infection with a significant faster median time to positivity of 6 days (range, 2 to 11 days) compared to 9 days in 47 cases with P. acnes identified as a contamination (P < 0.0001). In 15 of 70 (21.4%) patients with an infection, tissue samples were positive after day 7 and in 6 patients (8.6%) after day 10 when a blind subculture of the thioglycolate broth was performed. The highest sensitivity was detected for thioglycolate broth (66.3%) and the best positive predictive values for anaerobic agar plates (96.5%). A prolonged transportation time from the operating theater to the microbiological laboratory did not influence time to positivity of P. acnes growth. By reducing the cultivation time to 7 days, false-negative diagnoses would increase by 21.4%; thus, we recommend that biopsy specimens from bone and joint infections be cultivated to detect P. acnes for 10 days with a blind subculture at the end.

Propionic Acid Produced by Propionibacterium acnes Strains Contri-butes to Their Pathogenicity.

Propionibacterium acnes is an important member of the skin microbiome. The bacterium can initiate signalling events and changes in cellular properties in keratinocytes. The aim of this study was to analyse the effect of the bacterium on an immortalized human keratinocyte cell line. The results show that various P. acnes strains affect the cell-growth properties of these cells differentially, inducing cytotoxicity in a strain-specific and dose-dependent manner. We propose that bacterially secreted propionic acid may contribute to the cytotoxic effect. This acid has a role in maintaining skin pH and exhibits antimicrobial properties, but may also have deleterious effects when the local concentration rises due to excessive bacterial growth and metabolism. These results, together with available data from the literature, may provide insight into the dual role of P. acnes in healthy skin and during pathogenic conditions, as well as the key molecules involved in these functions.

An In vitro Model for Bacterial Growth on Human Stratum Corneum.

The diversity and dynamics of the skin microbiome in health and disease have been studied recently, but adequate model systems to study skin microbiotas in vitro are largely lacking. We developed an in vitro system that mimics human stratum corneum, using human callus as substrate and nutrient source for bacterial growth. The growth of several commensal and pathogenic bacterial strains was measured for up to one week by counting colony-forming units or by quantitative PCR with strain-specific primers. Human skin pathogens were found to survive amidst a minimal microbiome consisting of 2 major skin commensals: Staphylococcus epidermidis and Propionibacterium acnes. In addition, complete microbiomes, taken from the backs of healthy volunteers, were inoculated and maintained using this system. This model may enable the modulation of skin microbiomes in vitro and allow testing of pathogens, biological agents and antibiotics in a medium-throughput format.