Bacterial biofilms on PVC tubing's inner surface of hemodialysis water treatment system / 中南大学学报(医学版)

ABSTRACT

Objective To determine the morphology, bacteria and endotoxin content of bio-films on the inner surface of PVC tubes in hemodialysis water treatment system. Methods We dissolved biofilms of segments before and after reverse osmosis machine for bacterial count and identification. We studied biofilm structure of segments before and after reverse osmosis machine with eyes and scanning electron microscope. Biofilms of all 7 segments were dissolved for qualitative and quantitative assay of endotoxin. Results The inner surface of segment before reverse osmosis machine was homogeneously distributed with activated carbon powder deposition. The segment after reverse osmosis machine was normal. With scanning electron microscope, biofilm with successive surface and sandwich was found on the inner surface of segment before reverse osmosis machine, formed by clustering bacillus, activated carbon powder and some coccus. Bacteria of the same shape and length were found on segment after reverse osmosis machine, but fewer and looser. Bacterial culture and identification showed the former was mostly gram-negative bacillus, the latter was only a few micrococcus. Endotox-in of biofilm was between 2. 0 EU/mL and 4. 0 EU/mL. Quantitative assay showed segment after softener (2.821 ±0. 807) EU/mL; segment after active charcoal canister(3. 635 ±0. 427) EU/ mL; segment before reverse osmosis machine (3.687 ±0.271) EU/mL; segment after reverse osmosis machine (2. 041 ±0. 295) EU/mL; exit of power pump (1. 983 ±0. 390) EU/mL; the 1st dead space (2. 373 ± 0. 535) EU/mL; and the 2nd dead space (2. 858 ± 0. 690) EU/mL. Conclusion Biofilms are found on the inner surface of segment before and after reverse osmosis machine . Endotoxin level from high to low is as follows segment before reverse osmosis machine, segment after active charcoal canister, the 2 nd dead space, segment after softener, the 1 st dead space, segment after reverse osmosis machine, exit of power pump. The character of the bacteria and endotoxin of the biofilm can help us find better ways to control them.