Minimum inhibitory concentrations increase in Clostridioides difficile isolates from patients with recurrence: results from a retrospective single-centre cohort study

Background While antimicrobial susceptibility testing (AST) isn’t routinely performed for C. difficile infection (CDI), reports of antimicrobial resistance have increased in surveillance studies. The aim of this study was to assess the rate of antimicrobial resistance to four antimicrobials (vancomycin, metronidazole, tigecycline and ciprofloxacin), to assess risk factors for antimicrobial resistance and to evaluate MIC variation in patients with recurrence. Methods Data from consecutive patients with CDI admitted to our Istitution between the 1st of January 2022 and the 30th of April 2023 were collected. We performed AST with gradient diffusion and NAAT to evaluate presumptive presence of R027/NAP1 and toxin production genes. Results Antimicrobial susceptibility testing was performed on 108 available isolates. We didn’t found any isolate resistant to vancomycin, metronidazole and tigecycline, while all the isolates were resistant to ciprofloxacin. For 8 patients isolates from both first episode and recurrence were available: 3 (37.5%) displayed 2 fold MIC increase for vancomycin, 6 (75%) for metronidazole and 3 (37.5%) for tigecycline. Conclusions Our results were concordant with European surveillance data. MIC increase to all tested antibiotics in patients with CDI may be due to biofilm formation and its possible role warrant further research, especially considering reports of clinical failure due to vancomycin resistance.