A rebound technique ensures reproducible high levels of viable Pseudomonas aeruginosa in the dual-species Build-up Biofilm model used for endoscope channel cleaning validation

Recent clinical and experimental studies confirm that biofilm and/or buildup biofilm does lead to microbial survival after reprocessing in patient-ready endoscope channels. Current cleaning instructions for flexible endoscope channels cannot remove biofilm or build-up biofilm (BBF). The objective of this study was to develop a modified BBF (mBBF) protocol that has high reproducible levels of bacteria to assess how well manufacturer's cleaning protocols can remove mBBF. Pseudomonas aeruginosa and Enterococcus faecalis were used to form dual-species BBF in polytetrafluoroethylene (PTFE) channels of 3.7 mm ID (internal diameter) and in Air/water channel sets with 1.37 mm ID. The BBF-coated channels were then stored dry or wet and Colony forming unit (CFU)/cm2 was evaluated over a nine-day period to determine if "rebound" of matrix-embedded organisms would occur to reproducible high levels. In both 3.7 mm ID and 1.37 mm ID channels there was rebound of P. aeruginosa in mBBF wet channels that ranged from 5.5 (stdev 0.320) to 6.12 (stdev 0.07). There was some rebound of E. faecalis but it was sporadic and at low levels. The importance of friction for removal of mBBF in the air/water channels was demonstrated. The dual-species mBBF model allows replication of matrix-embedded P. aeruginosa to reliable, high CFU/cm2. This dual-species mBBF model provides a more stringent challenge for cleaning validation of endoscope channels.