Culture of Dialysis Fluids on Nutrient-Rich Media for Short Periods at Elevated Temperatures Underestimate Microbial Contamination

Abstract

Recommended culture methods for monitoring bacterial contamination of H₂O, dialysate and bicarbonate concentrate in dialysis centers in the USA involves culturing these fluids for 48 h at 37 °C. A variety of media and commercial culture methods are accepted for monitoring these fluids. Over a 3 month period a comparison was made between an acceptable culture method, tryptic soy agar (TSA) employing the pour plate (PP) technique at 37 °C for 48 h, and PP cultures on standard methods agar (SMA) and R2A agar, incubated at ambient temperature (23°C) for 48, 72, 168 h. Increases in the colony counts over time occurred for all three fluids. However, counts were greater on SMA and R2A than on TSA. The increases over the standard 48-hour TSA cultures ranged as high as 10⁴ times for 23°C cultures at 7 days of incubation. Endotoxin levels even in the most contaminated samples were found to be below the acceptable 5 EU/ml recommended for reprocessor water. Bacterial colonies that appeared at 48, 72 and 168 h were isolated and identified. Pseudomonas, Moraxella, Acinetobacter and CDC group VI C-2 were among some of the common bacteria isolated. This study indicates that the media utilized, the time and temperature of incubation may result in a significant underestimation of the bacterial population of water and dialysis fluids, thus potentially placing the patient at a higher risk.

Implementing On-Line Hemodiafiltration as a Renal Replacement Therapy for ICU Acute Renal Failure: A Single-Center Report of Feasibility, Safety and Hemodynamic Tolerance over a Seven-Year Period

“…Microbiological purity of fluids was assessed through the culture of the 0.45-µm ultrafilter membrane on a poor nutrient (R2A) medium at 20–22°C for 7 days, and expressed as CFU/ml [20,21]. UPW and dialysate were considered suitable according to the international guidelines (22, 23 and ISO 23500:2011 Guidance for the preparation and quality management of fluids for hemodialysis and related therapies) when microbiological count was less than 0.1 CFU/ml.…”

Microbiologic Purity of Dialysate:Rationale and Te chnical Aspects

“…They are summarized in table 1. Membrane filtration and culture on a poor or simple nutrient medium (R2A, Reasoner 2 Agar; TGE, Tryptone Glucose Extract) has been confirmed to be the more sensitive method to detect bacterial contamination [64]. Cultures will be incubated at room temperature (20-23°C) and observed for 5-7 days [65,66].…”

Renal replacement therapy review

“…Of note, the monitoring of such systems is also complicated by differing results of CFU counts dependent upon isolation technique, which will require appropriate techniques for evaluation of maintenance of published standards. 112,117 Peritoneal dialysis equipment. The equipment and fluids necessary for peritoneal dialysis require specific mention.…”