CULTURE OF DIALYSIS FLUIDS ON NUTRIENT-RICH MEDIA FOR SHORT PERIODS AT ELEVATED-TEMPERATURES UNDERESTIMATE MICROBIAL-CONTAMINATION

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 degrees C. A variet y of media and commercial culture methods are accepted for monitoring these fluids. Over a 3-month period a comparison was made between an a cceptable culture method, tryptic soy agar (TSA) employing the pour pl ate (PP) technique at 37 degrees C for 48 h, and PP cultures on standa rd methods agar (SMA) and R2A agar, incubated at ambient temperature ( 23 degrees C) for 48, 72, 168 h, Increases in the colony counts over t ime occurred for all three fluids. However, counts were greater on SMA and R2A than on TSA, The increases over the standard 48-hour TSA cult ures ranged as high as 10(4) times for 23 degrees 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 reproce ssor 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 st udy indicates that the media utilized, the time and temperature of inc ubation may result in a significant underestimation of the bacterial p opulation of water and dialysis fluids, thus potentially placing the p atient at a higher risk.