In Vitro Investigation of Auranofin as a Treatment for Clostridium difficile Infection

Abstract

Background: Clostridium difficile infection is the leading cause of hospital-acquired gastrointestinal infection and incidence rates continue to rise. Clostridium difficile infection is becoming increasingly complex to treat owing to the rise in treatment failures and recurrent infections. There is a clear need for new therapeutic options for the management of this disease.

Objective: This study aimed to assess auranofin, a drug approved for the treatment of arthritis, as a treatment for C. difficile infection. Previous investigations have demonstrated potential antimicrobial activity of auranofin against C. difficile and other organisms.

Methods: The activity of auranofin was assessed by in vitro investigations of its effect on C. difficile M7404 growth, vegetative cell viability, and spore viability. Activity of auranofin was also compared to that of the current treatments, metronidazole and vancomycin.

Results: Auranofin showed bactericidal activity at concentrations as low as 4.07 µg/mL, effectively reducing bacterial cell density by 50-70% and the viable vegetative cell and spore yields by 100%. The activity of auranofin was shown to be non-inferior to that of metronidazole and vancomycin.

Conclusions: Auranofin is highly efficacious against C. difficile M7404 in vitro and has the potential to be an ideal therapeutic option for the treatment of C. difficile infection.

Fig. 1

Bacterial growth of Clostridium difficile cultures treated with auranofin and ethanol. Auranofin-treated cultures are shown by a solid line and filled triangles, ethanol-treated cultures are shown by a small dashed line and a filled circle, and untreated control cultures are shown by a large dashed line and filled squares. The arrow at 10 h indicates the time of treatment with either auranofin 33.97 mg/L or 0.8% ethanol. ***p < 0.0005, n = 3. OD optical density

Fig. 2

Bacterial growth of Clostridium difficile cultures treated with auranofin. Treatment concentration of auranofin 33.97 mg/L is shown by a solid line with filled triangles, treatment concentration of auranofin 169.87 mg/L is shown by an alternating dashed line with unfilled triangles, treatment concentration of auranofin 339.75 mg/L is shown by a small dashed line with unfilled circles, and untreated cultures (control) are shown by a large dashed line with filled squares. The arrow at 12 h indicates the time of treatment. *Significant difference between cultures treated with auranofin 33.97 mg/L and the control, ⁺significant difference between cultures treated with auranofin 169.87 mg/L and the control, x indicates a significant difference between cultures treated with auranofin 339.75 mg/L and the control. All indicate a p value of < 0.005, n = 3. OD optical density

Fig. 3

Number of viable vegetative cells and spores from Clostridium difficile cultures treated with auranofin. Vegetative cell viability assessed from C. difficile cultures at a 12 h post-inoculation and b 24 h post-inoculation. Spore viability was assessed from C. difficile cultures at c 12 h post-inoculation and d 24 h post-inoculation. Treatment concentration of auranofin 33.97 mg/L is shown by filled triangles, treatment concentration of 169.87 mg/L is shown by unfilled triangles, treatment concentration of auranofin 339.75 mg/L is shown by unfilled circles, and untreated cultures (control) are shown by filled squares. *Significant difference between cultures treated with auranofin 33.97 mg/L and the control, ⁺significant difference between cultures treated with auranofin 169.87 mg/L and the control, x indicates a significant difference between cultures treated with auranofin 339.75 mg/L and the control. *p < 0.05; **p < 0.005, n = 3. CFU colony-forming unit

Fig. 4

Bacterial growth of Clostridium difficile cultures treated with auranofin, metronidazole, or vancomycin. Treatment with auranofin 4.08 mg/L (AS) is shown by a solid line with filled triangles, treatment with metronidazole 2.74 mg/L (MS) is shown by a small dashed line with unfilled triangles, treatment with vancomycin 11.59 mg/L (VS) is shown by an alternating dashed line with unfilled circles, and untreated cultures (control; C) are shown by a large dashed line with filled squares. *Significant difference between cultures treated with auranofin and the control, ⁺significant difference between cultures treated with vancomycin and the control, x indicates a significant difference between cultures treated with metronidazole and the control. All indicate a p value of < 0.005, n = 3. AS, C, MS, OD optical density, VS

Fig. 5

Number of viable vegetative cells and spores from Clostridium difficile cultures treated with auranofin, metronidazole, or vancomycin. Vegetative cell viability assessed from C. difficile cultures at a 12 h post-inoculation, b 24 h post-inoculation, and c 48 h post-inoculation. Spore viability was assessed from C. difficile cultures at d 12 h post-inoculation, e 24 h post-inoculation, and f 48 h post-inoculation. Treatment with auranofin 4.08 mg/L is shown by filled triangles, treatment with metronidazole 2.74 mg/L is shown by unfilled triangles, treatment with vancomycin 11.59 mg/L is shown by unfilled circles, and untreated cultures (control) are shown by filled squares, n = 3. CFU colony-forming unit