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Study by M. Alfa Helps Explain Contamination False Neg Tests

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Another recent study by a group led by Michelle Alfa, scientist and expert from Winnipeg quoted in the recent AAMI press release recommending the move to sterilization of endoscopes, shows the difficulties in culturing and determining whether a scope is contaminated with bacteria.. This helps to explain the huge variability of culture results in various studies, particularly those studies repeatedly demonstrating the inadequacy of existing practices with HLD systems. They recommend a new flush-brush-flush protocol for better identifying and establishing contamination of endoscopes. The difficulties with accurate and reliable culturing and identification of contamination (referred to as a degree of high false negative testing) suggests the contamination problem may be much larger and of more significance than previously understood. No wonder she and her team recommend the move to sterilization of endoscopes.

Gastrointestial Endoscopy journal

September 2017Volume 86, Issue 3, Pages 442–451.e1

A novel polytetrafluoroethylene-channel model, which simulates low levels of culturable bacteria in buildup biofilm after repeated endoscope reprocessing

Michelle J. Alfa, PhDCorrespondence information about the author PhD Michelle J. Alfa

, 

Maira M. Ribeiro, PhD

, 

Cristiana da Costa Luciano, PhD

, 

Rodrigo Franca, PhD

, 

Nancy Olson, BSc

, 

Pat DeGagne, RT

, 

Harminder Singh, MD

DOI: https://dx.doi.org/10.1016/j.gie.2017.05.014

 

Background and Aims

Clinical studies have shown variable culture results from flexible endoscope channels possibly because of low levels of bacteria that are difficult to extract. The aim of this study was to develop a simulated-use buildup biofilm (BBF) model that mimics low levels of viable bacteria after repeated rounds of aldehyde fixation and accumulation.

Methods

New endoscope channels were exposed to 8 days of repeated rounds of biofilm formation using ATS2015 containing Enterococcus faecalis and Pseudomonas aeruginosa, rinsing, fixation with glutaraldehyde, and rinsing. Viable count and scanning electron microscopy and borescope examination were used to compare the impact of dry storage over 26 weeks on the level of culturable bacteria and to compare the Centers for Disease Control and Prevention flush method of channel harvesting with a flush-brush-flush method.

Results

E faecalis (log10 6.6) and P aeruginosa (log10 8.6) accumulated over 8 days of cyclic biofilm formation and partial glutaraldehyde fixation, but after a final exposure to 2.6% glutaraldehyde the level of culturable bacteria was less than 2 log10. The Centers for Disease Control and Prevention channel harvesting method appeared by borescope to be inferior to a flush-brush-flush sample collection method for detection of viable bacteria. P aeruginosa increased up to 7 log10 after 26 weeks of dry storage, indicating there were viable but nonculturable bacteria present initially that recovered during storage.

Conclusions

Viable but nonculturable P aeruginosa within the BBF model are able to recover, and this phenomenon may explain the variability of culture in patient-used endoscopes. Our data also indicated that friction may be a critical part of sample collection from endoscope channels.