Bacteriology of hemodialysis fluids: are current methodologies meaningful?

Reports of increasing endotoxic reactions in dialysis centers using high-flux dialyzers and high contamination in liquid bicarbonate concentrates have resulted in concern for the microbial contamination of dialysate. The influence of salt-supplemented media on the recovery of bacterial contaminants from the fluids used in hemodialysis has been examined. This study found a negative influence of a 2% NaCl supplementation of growth media for both purified water and dialysate. Salt-supplemented pour plate cultures of bicarbonate concentrate samples were not statistically different from nonsupplemented cultures (p = 0.2). The influence of the bicarbonate salt on recovery in the pour plates was not addressed. The different media recommended for monitoring microbial contamination of dialysis fluids were compared. As previously reported, both water and dialysate collected from a relatively large geographic area showed higher recoveries on Reasoner's R2A agar than on media recommended by the Association for Advancement of Medical Instrumentation (AAMI) standards (p < 0.0001). Standard methods agar (SMA) and trypticase soy agar (TSA) produced the next highest recovery for water and dialysate, respectively. The higher recoveries generally observed on R2A or SMA suggest that to provide better patient safety these media should be selected for monitoring bacterial contamination of water, and R2A, SMA, or TSA for dialysate. The variability in the species identified across the three fluids and variability in counts observed in the different fluids suggest that significant dialysate contamination may occur from sources other than the water and bicarbonate concentrates.