Foot infections are a major cause of morbidity in people with diabetes and the most common cause of diabetes-related hospitalization and lower extremity amputation. Staphylococcus aureus is by far the most frequent species isolated from these infections. In particular, methicillin-resistant S. aureus (MRSA) has emerged as a major clinical and epidemiological problem in hospitals. MRSA strains have the ability to be resistant to most β-lactam antibiotics, but also to a wide range of other antimicrobials, making infections difficult to manage and very costly to treat. To date, there are two fifth-generation cephalosporins generally efficacious against MRSA, ceftaroline and ceftobripole, sharing a similar spectrum. Biofilm formation is one of the most important virulence traits of S. aureus. Biofilm growth plays an important role during infection by providing defence against several antagonistic mechanisms. In this study, we analysed the antimicrobial susceptibility patterns of biofilm-producing S. aureus strains isolated from diabetic foot infections. The antibiotic minimum inhibitory concentration (MIC) was determined for ten antimicrobial compounds, along with the minimum biofilm inhibitory concentration (MBIC) and minimum biofilm eradication concentration (MBEC), followed by PCR identification of genetic determinants of biofilm production and antimicrobial resistance. Results demonstrate that very high concentrations of the most used antibiotics in treating diabetic foot infections (DFI) are required to inhibit S. aureus biofilms in vitro, which may explain why monotherapy with these agents frequently fails to eradicate biofilm infections. In fact, biofilms were resistant to antibiotics at concentrations 10–1000 times greater than the ones required to kill free-living or planktonic cells. The only antibiotics able to inhibit biofilm eradication on 50 % of isolates were ceftaroline and gentamicin. The results suggest that the antibiotic susceptibility patterns cannot be applied to biofilm established infections. Selection of antimicrobial therapy is a critical step in DFI and should aim at overcoming biofilm disease in order to optimize the outcomes of this complex pathology.

The rise of multidrug-resistant (MDR) bacteria, particularly carbapenem-resistant Enterobacterales (CRE), poses a significant threat to public health. Infections caused by CRE, such as Escherichia coli and Klebsiella pneumoniae , are associated with high rates of antibiotic treatment failure. β-lactam antibiotics, like meropenem, remain crucial in treating these infections, but their efficacy is undermined by β-lactamase production. This study investigates the potential of APC24-7, a novel broad-spectrum β-lactamase inhibitor (BLi) with dual activity, to restore antimicrobial activity of meropenem against CRE clinical isolates. The in-vitro analysis of a diverse panel of clinically relevant E. coli and K. pneumoniae isolates expressing both serine- and metallo-β-lactamases demonstrated that APC24-7 effectively restored meropenem activity by reducing the minimum inhibitory concentrations (MICs) to below breakpoint. Time-kill assays confirmed that the combination therapy showed dose-dependent bacterial killing, with significant potentiation of meropenem activity against isolates expressing both serine- and metallo-β-lactamases. In-vivo efficacy evaluation in a murine thigh infection model further confirmed APC24-7’s potential to restore meropenem efficacy against meropenem resistant strains. These findings suggest that APC24-7offers a promising strategy to combat infections caused by β-lactamase-producing Enterobacterales .

Background: Carbapenem-resistant Enterobacterales (CRE) represent a major therapeutic challenge, driven in part by serine β-lactamases (SBLs) and metallo-β-lactamases (MBLs). APC24-7 is a broad-spectrum β-lactamase inhibitor (BLI) designed to inhibit enzymes from both groups. Here, we evaluated the ability of APC24-7 to potentiate meropenem (MEM) activity against meropenem-resistant Escherichia coli and Klebsiella pneumoniae. Methods & Results: Checkerboard assays were performed against 31 K. pneumoniae and 17 E. coli isolates harboring a range of clinically relevant SBL and/or MBL genes. APC24-7 reduced meropenem minimum inhibitory concentrations (MICs) in an isolate- and concentration-dependent manner. At 32 mg/L APC24-7, meropenem MICs fell within the CLSI susceptible range for meropenem in 11 of 17 E. coli isolates, whereas 16 of 31 K. pneumoniae isolates remained resistant. Time-kill experiments with nine selected isolates showed bactericidal activity under active combination conditions, defined as a ≥3 log10 CFU/mL reduction from the initial bacterial count, within 3–5 h. Pharmacokinetic evaluation in infected mice showed less-than-dose-proportional systemic exposure following subcutaneous administration of APC24-7, with a maximum plasma concentration of approximately 26 mg/L after a 30 mg/kg dose. In a neutropenic murine thigh infection model, APC24-7 increased meropenem activity against four selected in vitro-responsive isolates in a dose-dependent manner. Conclusions: These findings provide preclinical proof of concept for APC24-7 as a broad-spectrum BLI capable of potentiating meropenem against Enterobacterales harboring diverse β-lactamases, while highlighting substantial isolate-dependent variability that warrants further pharmacokinetic/pharmacodynamic and resistance-mechanism studies.