Introduction Approximately 20% of patients with Clostridium difficile (CD) infection relapse after initially effective treatment. These typically occur 3–10 days after cessation of standard antibiotic therapy with vancomycin or metronidazole. Some patients relapse 2 or even 3 times, each requiring additional courses of antibiotics. The general consensus is that relapse occurs either because CD had not been completely eradicated by the antibiotics, or because spores are resistant to killing. Several days post-antibiotics, surviving spores transform into active bacterial forms again which multiply to produce toxins again. This study aimed to combine PACT, which we have shown to be effective against CD, with a novel strategy called germinant therapy.

Methods Germinant therapy with two phase PACT was evaluated against the hypervirulent R20291 strain of CD with photosensitisers (PS) we have found to effectively kill CD from earlier studies. Plates containing CD were treated with a single PACT treatment, pre and post germination of quiescent spores with the bile salt taurocholate.

Results PACT effectively killed R20291 at doses > 10 μM after exposure to laser light at 665nm at an intensity of 24 mJ/cm2. However, post PACT treatment of the C. difficile culture with the spore germinant taurocholate showed that 100% of CD spores were resistant to the treatment. Remarkably, it was shown that pre-incubation of CD spores in germination conditions for 30 minutes prior to PACT leads to > 99.9% kill of the initial number of spores permitting the killing of CD in both its vegetative and sporulating form. Moreover, toxicity of taurocholic acid was excluded in HT-29 colon cells.

Conclusion The presented study describes applicability for PACT in the successful treatment of highly resistant CD spores using a two-phase antimicrobial approach and that taurocholic acid is non-toxic to humans. This strategy could be effective at reducing the significant numbers of patients with relapsing CD, the length of stay for these patients, associated morbidity as well as the potential mortality of CD which mostly arises from this sub-group of patients.

Disclosure of Interest None Declared.