Bacterial Contamination of Hemodialysis Center Water and Dialysate: Are Current Assays Adequate?

Abstract

Many dialysis centers depend on clinical laboratories or a commercially available dip culture to determine the contamination levels in water and dialysate. To determine whether these standard clinical culture procedures adequately quantitate bacterial contamination in hemodialysis center water and dialysate, test results of two routine clinical media was compared, trypticase soy agar (TSA) and plate count agar (PCA), with those of nutrient-poor R2A medium. Dialysate samples demonstrated significant differences in media, the temperature of incubation, and plating techniques (pour plate versus spread plates). Purified water for dialysis demonstrated significant differences only for media; however, temperature was an important variable. Selective growth on R2A agar of some water- and dialysate-contaminating species was studied by velvet disk and loop transfer of colonies. A strong selectivity for water-borne bacteria was demonstrated by R2A agar; the bacteria that did not grow on TSA and PCA have been identified.

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

“…Nutrient-rich media tend to underestimate the bacterial contamination of purified water and dialysate fluids as observed in previous studies [1][2][3][4]. Hardinget al [I] reported that elevated temperature tends to produce lower colony counts than lower temperatures.…”

“…As observed previously [1], it is difficult to perform quantitative assays on isolates due to laboratory adaptation of the organisms. This assay, however, establishes that the same organisms may produce observ able colonies at different rates and that some organisms fail to grow at all on TSA.…”

“…[5] reported no statistical differ ences in their colony counts at different incu bation times and temperatures. However, Harding et al [1,4] observed a very large per centage of low nutrient, low temperature and extended incubation time cultures having higher counts than the bench mark tryptic soy agar (TSA) culture medium. They frequently observed counts on low nutrient media that were several orders of magnitude higher than the standard nutrient-rich media cultured at 37°C (physiological) temperature employed for clinical isolates [4], Increasingly the dialysis literature indi cates that there are small molecular weight bacterial products in contaminated dialysates that are able to pass through the lowest perme ability cellulosic dialysis membranes by diffu sion or backfiltration and stimulate the pro duction of cytokines [6][7][8][9][10][11][12], Contaminated dialysate has been implicated in the produc tion of the amyloid deposits that are frequent ly observed in long-term dialysis patients [13], Inadequate monitoring practices in the dialy sis center obviate the probability of inade quate sanitization frequency and/or tech niques.…”

Chlorine Dioxide: A New Agent for Dialysis Monitor Disinfection in a Pediatric Center

“…The medium used, plate count agar, could have caused less bacterial growth compared with other media such as trypticase soy agar and nutrient-poor R2A medium (R2A) rec ommended by a few authors for dialysis fluid examination [5,6,18]. However, in a recent comparison between plate count agar and R2A.…”

Water Treatment for Hemodialysis

“…In a recent study, bacterial growth of dialysate samples in standard culture media, trypticase soy agar or plate count agar, was com pared to results obtained in a nutrient poor R2A medium, cultured at 25 °C for 96 h [79]. Several typical water bac teria grew better or more selectively on R2A agar.…”