Development and characterisation of an in vitro human gut model to study the biofilm mode of growth of clostridium difficile and the indigenous gut microbiota

Clostridium difficile infection (CDI) is associated with significant patient morbidity, mortality and financial burden. Until recently, antimicrobial treatment options were limited to metronidazole and vancomycin, but both agents are associated with recurrence rates of approximately 20%. The human gastrointestinal tract harbours a complex microbial community which exist in planktonic and sessile form. Sessile organisms are known to cause chronic infection such as cystic fibrosis. Mucosal biofilms exist on surfaces of the gastrointestinal tract, but the existence and role of C. difficile in these structures remains unknown. The present study describes the process undertaken to adapt and validate an in vitro human gut model to study the planktonic and biofilm mode of growth of C. difficile and the indigenous gut microbiota. A triple stage chemostat gut model, primed with a human faecal emulsion was used to induce and treat simulated CDI. A glass rod system was incorporated into the third vessel to facilitate the formation and subsequent analysis of mixed-species biofilms. Sessile and planktonic gut microbiota and C. difficile populations within an in vitro gut model are similar in the absence of antimicrobial intervention. Differences in behaviours of the two modes of growth are evident upon antimicrobial administration, with a delayed response in sessile populations. The sessile mode of growth of C. difficile within mature biofilm structures is complex and variable. Within the redesigned biofilm gut model, sessile C. difficile remained in spore form for the duration of the experiment, despite induction of simulated CDI, treatment of CDI and recurrence of disease evident within planktonic communities. Recalcitrant spores within biofilms may be seeded into the planktonic fluid of the gut model after apparent successful initial treatment and contribute to recurrence of CDI. The role of sessile C. difficile in recurrent CDI should be further investigated.