In vitro Activity of Dalbavancin and Fourteen Other Antimicrobial Agents against Toxigenic <i>Clostridioides difficile</i> Clinical Isolates in a Greek Tertiary-Care Hospital

Objective: Clostridioides difficile is a major cause of healthcare-associated diarrhea worldwide. For years, metronidazole and vancomycin were considered the standard treatment for C. difficile infection. However, they are increasingly being associated with treatment failure and recurrence. In this study, we investigated the in vitro activity of dalbavancin and fourteen other antimicrobials against 155 toxigenic C. difficile isolates originating from patients with C. difficile-associated diarrhea. Materials and Methods: Antimicrobial susceptibility was evaluated by the MIC Test Strip, and the results were interpreted using both the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. Results: C. difficile isolates were fully susceptible to metronidazole, vancomycin, amoxicillin/clavulanate, piperacillin/tazobactam, and tigecycline. All isolates were dalbavancin susceptible by the CLSI breakpoint (≤0.25 μg/mL) compared with 97.4% susceptibility by the EUCAST breakpoint (≤0.125 μg/mL). Dalbavancin demonstrated significantly lower MIC₅₀ and MIC₉₀ values compared to vancomycin (0.047 vs. 0.38 and 0.125 vs. 0.5, respectively, p < 0.001). Resistance rates to penicillin, ampicillin, cefoxitin, imipenem, meropenem, clindamycin, moxifloxacin, chloramphenicol, and tetracycline were 20%, 14.2%, 100%, 75.5%, 0.6%, 51%, 36.1%, 3.2%, and 14.8%, respectively. Multidrug-resistant phenotypes were detected among 41.3% of the isolates. Conclusion: Dalbavancin exhibited potent activity against the isolates tested. As C. difficile is an important healthcare-associated pathogen, continued surveillance is required to monitor for development of resistance.