Mammalian cells produce and metabolize almost exclusively L-lactate, bacterial species have the capacity to produce both D-lactate and L-lactate. The aim of this study was to evaluate the intrinsic production of D- and L-lactate in the most common pathogenic microorganisms causing septic arthritis (SA) and periprosthetic joint infection (PJI) as a potential biomarker for the diagnosis of infection. Following microorganisms were grown according to ATCC culture guides and tested for production of D- and L-lactate: Staphylococcus aureus (ATCC 43300), Staphylococcus epidermidis (ATCC 35984), Enterococcus faecalis (ATCC 19433), Streptococcus pyogenes (ATCC 19615), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Cutibacterium acnes (ATCC 11827), and Candida albicans (ATCC 90028). Pathogens were inoculated in 8 ml of appropriate liquid media and incubated as planktonic or biofilm form in either aerobic, anaerobic or CO₂ atmosphere up to 312 h. D- and L-lactate measurements were performed at different time points: 0, 6, 9, 12 and 24 h, then once per day for slow-growing pathogens. Samples were serially diluted and plated for colony counting. Liquid culture media without microorganisms served as a negative control. Production of D-lactate was observed in all tested microorganisms, whereas no L-lactate was detected in E. coli, P. aeruginosa, and C. albicans. Maximal concentration of D-lactate was produced by S. aureus (10.99 mmol/L), followed by E. coli (1.22 mmol/L), and S. epidermidis (0.48 mmol/L). Maximal L-lactate concentration was observed in S. pyogenes (10.12 mmol/L), followed by S. aureus (9.71 mmol/L), E. faecalis (2.64 mmol/L), and S. epidermidis (2.50 mmol/L). S. epidermidis bacterial biofilm produced significantly higher amount of D- and L-lactate compared to planktonic form (p = 0.015 and p = 0.002, respectively). Our study has demonstrated that the most common pathogenic microorganisms causing SA and PJI have the capability to generate measurable amounts of D-lactate in both planktonic and biofilm form, highlighting the practical value of this biomarker as an indicator for bacterial and fungal infections. In contrast to D-lactate, the absence of L-lactate production in certain tested bacteria, as well as in fungi, suggests that L-lactate is not eligible as a biomarker for diagnosing microbial infections.

Candida auris has emerged globally as a multidrug-resistant fungal pathogen. Isolates of C. auris are reported to be misidentified as Candida haemulonii. The aim of the study was to compare the heat production profiles of C. auris strains and other Candida spp. and evaluate their antifungal susceptibility using isothermal microcalorimetry. The minimum heat inhibitory concentrations (MHIC) and the minimum biofilm fungicidal concentration (MBFC) were defined as the lowest antimicrobial concentration leading to the lack of heat flow production after 24 h for planktonic cells and 48 h for biofilm-embedded cells. C. auris exhibited a peculiar heat production profile. Thermogenic parameters of C. auris suggested a slower growth rate compared to Candida lusitaniae and a different distinct heat profile compared to that of C. haemulonii species complex strains, although they all belong to the Metschnikowiaceae clade. Amphotericin B MHIC and MBFC were 0.5 µg/mL and ≥8 µg/mL, respectively. C. auris strains were non-susceptible to fluconazole at tested concentrations (MHIC > 128 µg/mL, MBFC > 256 µg/mL). The heat curve represents a fingerprint of C. auris, which distinguished it from other species. Treatment based on amphotericin B represents a potential therapeutic option for C. auris infection.

Multi-drug resistant Gram-negative pathogens are increasingly difficult-to-treat perpetrators of infections. New, innovative, and more multifaceted therapies for the treatment of multi-drug resistant strains are thus urgent to hinder further drug resistance and mitigate deadly, untreatable infections. Our study aimed to investigate the efficacy of cefiderocol against Gram-negative aerobic bacteria alone and in combination with phages. The minimum inhibitory concentration (MIC) of cefiderocol was determined using the microdilution broth method, while the minimum biofilm bactericidal concentration was assessed using isothermal microcalorimetry. The combined effect of cefiderocol and phages was evaluated using colony-forming unit counts. Results demonstrated a notable antibacterial effect of cefiderocol, with 83.4% of tested strains exhibiting susceptibility. When combined with phages, the MIC of cefiderocol was reduced by 2–64-fold, indicating a synergistic interaction between the two agents. Furthermore, the combination therapy showed enhanced efficacy against biofilm compared to monotherapy with either cefiderocol or phages alone, leading to complete biofilm elimination in certain cases. This study highlights the potential of combining cefiderocol with phages as a strategy to combat multi-drug resistant Gram-negative bacterial infections. The observed synergy suggests that this combination therapy could improve treatment outcomes and help address the challenges of antibiotic resistance and biofilm-associated infections.

Aims: The aim of this study was to evaluate the clinical and microbiological characteristics, surgical and antibiotic strategies, and long-term outcomes in patients with polymicrobial periprosthetic joint infection (PJI). Methods: This retrospective cohort study was undertaken at a tertiary healthcare centre and included patients aged ≥ 18 years with polymicrobial PJI treated with two-stage or multistage exchange of implants between January 2013 and May 2020. The modified European Bone and Joint Infection Society (EBJIS) criteria were used for the diagnosis of PJI. Surgical and antibiotic treatment followed a standardized institutional algorithm. Outcomes were assessed using Delphi international multidisciplinary consensus criteria and function was classified into categories of mobility. Statistical analyses included Kaplan-Meier survival curves and logistic regression for the identification of risk factors. Results: A total of 39 patients were included; 24 hip and 15 knee PJIs. Staphylococci (n = 26; 67%), Gram-negative bacilli (n = 15; 38%), and enterococci (n = 14; 36%) were the most frequently isolated pathogens. The median interval between explantation and reimplantation was 91 days, with a median of three revisions required for infection control. Postoperative antibiotic regimens commonly included β-lactams with glycopeptides or lipopeptides, followed by biofilm-active oral antibiotics. The rates of infection-free survival at one, two, and three years were comparable for hip and knee PJIs (76% (95% CI 52 to 89) and 65% (95% CI 31 to 85), respectively; p = 0.121), but there was signicantly better long-term survival after four years for hip PJIs (76% (95% CI 52 to 89) vs 43% (95% CI 9 to 75); p < 0.001). Recurrent infection occurred in ten patients (26%), with difficult-to-treat (DTT) pathogens significantly influencing the failure of treatment. Functional outcomes varied, with 13 patients (33%) regaining independent mobilization. Conclusion: Polymicrobial PJI remains a difficult condition to treat, with high morbidity requiring a tailored multidisciplinary approach. While standardized surgical and antibiotic strategies improve infection control, DTT organisms, and previous revision procedures increase the risk of recurrent infection. The poor long-term functional outcomes highlight the need for further optimization of treatment protocols to enhance patients’ mobility and quality of life. Cite this article: Bone Joint J 2025;107-B(12):1288–1294.