Risk of cell-culture contamination is a common concern whenever materials are added to or removed from a bioreactor. It is essential to maintain a sterile barrier and provide containment against intruding organisms during such operations. Many R&D and pilot-scale manufacturing tasks involve flexible, single-use processes with presterilized containment systems in nonclassified laboratory areas. Here, we examine a process that requires substantial manipulation of a culture — first completely removing and later returning the culture to a bioreactor during media exchange…