Staphylococcus aureus is a skin commensal microorganism commonly colonizing healthy humans. Nevertheless, S. aureus can also be responsible for cutaneous infections and contribute to flare-up of inflammatory skin diseases such as atopic dermatitis (AD), which is characterized by dysbiosis of the skin microbiota with S. aureus as the predominant species. However, the role of major virulence factors of this pathogen such as phenol-soluble modulin (PSM) toxins in epidermal inflammation remains poorly understood. Stimulation of primary human keratinocytes with sublytic concentrations of synthetic and purified PSM α3 resulted in upregulation of a large panel of pro-inflammatory chemokine and cytokine gene expression, including CXCL1, CXCL2, CXCL3, CXCL5, CXCL8, CCL20, IL-1α, IL-1β, IL-6, IL-36γ and TNF-α, while inducing the release of CXCL8, CCL20, TNF-α and IL-6. In addition, using S. aureus culture supernatant from mutants deleted from genes encoding either α-type PSMs or all PSM production, PSMs were shown to be the main factors of S. aureus secretome responsible for pro-inflammatory mediator induction in human keratinocytes. On the other hand, α-type PSM-containing supernatant triggered an intense induction of pro-inflammatory mediator expression and secretion during both topical and basal layer stimulation of an ex vivo model of human skin explants, a physiologically relevant model of pluristratified epidermis. Taken together, the results of this study show that PSMs and more specifically α-type PSMs are major virulence factors of S. aureus inducing a potent inflammatory response during infection of the human epidermis and could thereby contribute to AD flare-up through exacerbation of skin inflammation.

Currently, no guideline provides recommendations on the duration of empirical antimicrobial treatment (EAT) in prosthetic joint infection (PJI). The aim of our study was to describe the time to growth of bacteria involved in PJI, rendering possible decreased duration of EAT. Based on a French multicentre prospective cohort study, culture data from patients with confirmed hip or knee PJI were analysed. For each patient, five samples were processed. Time to positivity was defined as the first positive medium in at least one sample for virulent pathogens and as the first positive medium in at least two samples for commensals. Definitive diagnosis of polymicrobial infections was considered the day the last bacteria were identified. Among the 183 PJIs, including 28 polymicrobial infections, microbiological diagnosis was carried out between Day 1 (D1) and D5 for 96.7% of cases. There was no difference in the average time to positivity between acute and chronic PJI (p = 0.8871). Microbiological diagnosis was given earlier for monomicrobial than for polymicrobial infections (p = 0.0034). When an optimized culture of peroperative samples was carried out, almost all cases of PJI were diagnosed within five days, including polymicrobial infections. EAT can be re-evaluated at D5 according to microbiological documentation.

The inoculum effect (i.e., reduction in antimicrobial activity at large starting inoculum) is a phenomenon described for various pathogens. Given that limited data exist regarding inoculum effect of Acinetobacter baumannii , we evaluated killing of A. baumannii by polymyxin B, a last-resort antibiotic, at several starting inocula and developed a PKPD model to capture this phenomenon. In vitro static time-kill experiments were performed using polymyxin B at concentrations ranging from 0.125 to 128 mg/L against a clinical A. baumannii isolate at four starting inocula from 10 ⁵ to 10 ⁸ CFU/mL.

Lower respiratory tract infections (LRTIs) place a substantial burden on emergency departments (EDs) during winter outbreaks. Their microbiological diagnosis is currently based on either broad-spectrum molecular techniques performed in laboratory, with turnaround times incompatible with ED workflows, or point-of-care systems, restricted to SARS-CoV-2, influenza A/B, and RSV (quadriplex panel). The Spotfire combines rapid result and syndromic approach (10 respiratory viruses and 4 atypical bacteria), but its added value in EDs remains unassessed. During the 2023 winter, trained nurses collected nasopharyngeal swabs from adult patients with LRTI symptoms and operated the Spotfire in the ED of the Poitiers University Hospital. We described the viral epidemiology and evaluated the impact and efficacy of this rapid broad-spectrum diagnosis by comparing the management of patients with or without respiratory pathogen detected. From 15 December 2023 to 15 March 2024, 1,320 samples were analyzed with Spotfire, with a median turnaround time of 37 min and 10 uninterpretable results. A total of 540 (41%) were positive. Influenza A (30.9%), rhinovirus/enterovirus (21.1%), and SARS-CoV-2 (18.7%) were the main viruses detected, while atypical bacteria represented 8% of all pathogens. Overall, a pathogen not represented on the quadriplex panel was detected in 43% samples. Positive test results were associated with faster medical decision (380 ± 234 vs 431 ± 238 min; P < 0.001), fewer hospital admissions (65% vs 78%; P < 0.001), and shorter hospital stay (10 ± 9 vs 12 ± 14 days; P = 0.006) than negative test results. Antibiotic therapy was administered to 42 of 43 of Mycoplasma pneumoniae -positive patients (98%) compared with 110 of 1,265 (9%) negative patients. This study validated the feasibility of this new diagnostic tool in high-volume EDs improving patient flow, antimicrobial decisions, and isolation strategies. IMPORTANCE: This study provides the first real-world evidence supporting the use of a broad multiplex PCR platform for respiratory pathogens directly at the point of care in a high-volume emergency department. By enabling the simultaneous detection of 14 viruses and atypical bacteria within 20 min, this system bridges a critical gap between laboratory diagnostics and bedside clinical decision-making. Its implementation proved feasible and reliable, improving patient flow, antimicrobial stewardship, and infection control measures. Nearly half of the pathogens identified would have been missed by conventional quadriplex assays, highlighting the added diagnostic value of broader syndromic coverage. These findings are of interest to both clinicians and microbiologists, as they provide pragmatic evidence to guide the integration of advanced molecular diagnostics into acute-care workflows and to optimize patient management during respiratory infection surges.