Prosthetic joint infection (PJI) caused by Pseudomonas aeruginosa represents a severe complication in orthopaedic surgery. We report the case of a patient with chronic PJI from P. aeruginosa successfully treated with personalised phage therapy (PT) in combination with meropenem. A 62-year-old woman was affected by a chronic right hip prosthesis infection since 2016 caused by P. aeruginosa. The patient was treated with phage Pa53 (I day 10 ml q8h, then 5 ml q8h via joint drainage for two weeks) in association with meropenem (2gr q12h iv) after a surgical procedure. A two-year clinical follow-up was performed. An in vitro bactericidal assay of the phage alone and in combination with meropenem against a 24h-old biofilm of bacterial isolate was also carried out. No severe adverse events were observed during PT. Two years after suspension there were no clinical signs of infection relapse, and a marked leukocyte scan showed no pathological uptake areas. In vitro studies showed that the minimum biofilm eradicating concentration of meropenem was 8 µg/ml. No biofilm eradication was observed at 24h incubation with phages alone (10⁸ PFU/ml). However, the addition of meropenem at sub-eradicating concentration (1µg/ml) to phages at lower titer (10³ PFU/ml) resulted in a synergistic eradication after 24h incubation. Personalized PT, in combination with meropenem, was found to be safe and effective in eradicating P. aeruginosa infection. These data encourage the development of personalized clinical studies aimed at evaluating the efficacy of PT as an adjunct to antibiotic therapy for chronic persistent infections.

HIV-1 non-B subtypes/circulating recombinant forms (CRFs) are increasing worldwide. Since subtype identification can be clinically relevant, we assessed the added value in HIV-1 subtyping using updated molecular phylogeny (Mphy) and the performance of routinely used automated tools. Updated Mphy (2015 updated reference sequences), used as a gold standard, was performed to subtype 13,116 HIV-1 protease/reverse transcriptase sequences and then compared with previous Mphy (reference sequences until 2014) and with COMET, REGA, SCUEAL, and Stanford subtyping tools. Updated Mphy classified subtype B as the most prevalent (73.4%), followed by CRF02_AG (7.9%), C (4.6%), F1 (3.4%), A1 (2.2%), G (1.6%), CRF12_BF (1.2%), and other subtypes (5.7%). A 2.3% proportion of sequences were reassigned as different subtypes or CRFs because of misclassification by previous Mphy. Overall, the tool most concordant with updated Mphy was Stanford-v8.1 (95.4%), followed by COMET (93.8%), REGA-v3 (92.5%), Stanford-old (91.1%), and SCUEAL (85.9%). All the tools had a high sensitivity (≥98.0%) and specificity (≥95.7%) for subtype B. Regarding non-B subtypes, Stanford-v8.1 was the best tool for C, D, and F subtypes and for CRFs 01, 02, 06, 11, and 36 (sensitivity, ≥92.6%; specificity, ≥99.1%). A1 and G subtypes were better classified by COMET (92.3%) and REGA-v3 (98.6%), respectively. Our findings confirm Mphy as the gold standard for accurate HIV-1 subtyping, although Stanford-v8.1, occasionally combined with COMET or REGA-v3, represents an effective subtyping approach in clinical settings. Periodic updating of HIV-1 reference sequences is fundamental to improving subtype characterization in the context of an effective epidemiological surveillance of non-B strains.

Staphylococcus aureus implant-associated infections are difficult to treat because of the ability of bacteria to form biofilm on medical devices. Here, the efficacy of Sb-1 to control or prevent S. aureus colonization on medical foreign bodies was investigated in a Galleria mellonella larval infection model. For colonization control assays, sterile K-wires were implanted into larva prolegs. After 2 days, larvae were infected with methicillin-resistant S. aureus ATCC 43300 and incubated at 37 °C for a further 2 days, when treatments with either daptomycin (4 mg/kg), Sb-1 (10⁷ PFUs) or a combination of them (3 x/day) were started. For biofilm prevention assays, larvae were pre-treated with either vancomycin (10 mg/kg) or Sb-1 (10⁷ PFUs) before the S. aureus infection. In both experimental settings, K-wires were explanted for colony counting two days after treatment. In comparison to the untreated control, more than a 4 log¹⁰ CFU and 1 log¹⁰ CFU reduction was observed on K-wires recovered from larvae treated with the Sb-1/daptomycin combination and with their singular administration, respectively. Moreover, pre-infection treatment with Sb-1 was found to prevent K-wire colonization, similarly to vancomycin. Taken together, the obtained results demonstrated the strong potential of the Sb-1 antibiotic combinatory administration or the Sb-1 pretreatment to control or prevent S. aureus-associated implant infections.

Objectives The main aim of this study was to evaluate the antibiofilm activity of cefiderocol alone and in combination with imipenem versus sessile cells of Pseudomonas aeruginosa, assessing a potential synergistic bactericidal effect. Methods Ten P. aeruginosa clinical isolates from infected implants and bloodstream were included in the study. Cefiderocol was tested alone and in combination with imipenem on 24 hour-old P. aeruginosa biofilm formed on porous glass beads. For each antibiotic formulation, minimum bactericidal biofilm concentration (MBBC), defined as the lowest concentration that determined a reduction of at least 3-log10 CFU/mL compared to the untreated control, was evaluated. Scanning electron microscopy (SEM) was used to investigate the biofilm of P. aeruginosa treated with cefiderocol, imipenem or their combination. Results Cefiderocol and imipenem were tested alone on P. aeruginosa biofilm and a reasonable reduction in the number of viable cells was observed especially at high drugs concentrations tested. The synergistic effect of cefiderocol in combination with imipenem was evaluated for five selected isolates. Co-treatment with the two drugs led to a remarkable reduction of cell viability, by resulting in synergistic bactericidal activity in all tested strains and in synergistic eradicating activity in only one isolate. SEM analysis revealed that in cefiderocol-treated biofilm, bacterial cells became more elongated than those of the untreated control, forming filaments in which bacterial division seems to be inhibited. Conclusions Cefiderocol exhibited an encouraging antibiofilm activity against tested strains, representing a valid option for the treatment of P. aeruginosa biofilm-associated infections, especially when administered in combination with imipenem.