Abstract: 【Abstract】Objective To study the diversity and growth characteristics of culturable microorganisms in hemodialysis water in Qinghai Province and to identify their contamination risk, in order to provide data support for improving the quality of dialysis water. Methods Hemodialysis water samples were collected from the delivery port of the reverse osmosis unit and the return port of the water pipeline in the hemodialysis centers of 18 hospitals. The bacteria in water were enriched by a membrane filtration method and then cultured in tryptone glucose extract agar (TGEA) and R2A agar medium (R2A) at 21℃ for 7 days. Colonies were dynamically observed and counted. The culturable bacteria were identified by mass spectrometry and PCR methods. Results Twelve Gram- negative bacteria and 7 Gram- positive bacteria were detected. The proportions of Gram-negative bacteria were 79.78% and 95.76%, higher than the proportions of Gram-positive bacteria of 20.22% and 4.24%, in water from return port and delivery port respectively. The number of Methylobacterium fujisawasense was 31.32 CFU/mL in water from delivery port, higher than that of 0.36 CFU/mL in water from return port (U=5026.500, P<0.001). The numbers of Ralstonia pickettii, Sphingomonas echinoides and Methylobacterium fujisawasense growing on TGEA were 10.64, 7.10 and 62.16 CFU/ml respectively, more than the
numbers growing on R2A of 0.82, 6.10 and 29.36 CFU/mL respectively (U=29721.000, 127168.000 and 1808717.5 respectively, P<0.001). Most bacteria entered the stabilization stage at the 5th day of incubation, but Methylobacterium fujisawasense and Sphingomonas echinoides progressed into the logarithmic growth stage at the 6th day of incubation. Conclusions The culturable microorganisms in dialysis water from delivery port and return port are mainly G- bacteria with substantial differences in the distribution of genus and species. The delayed growth peak in some bacteria suggests that incubation for 168 hours (7 days) may underestimate the level of microbial contamination in water. If the determination of bacterial species were solely based on morphological characteristics of the colonies in the processes of colony growth, the results would be biased. The knowledge about the diversity, species distribution and growth characteristics of bacteria in hemodialysis water is useful for the detection of bacterial contamination risk and the improvement of surveillance standards for dialysis water quality.

Key words: Hemodialysis water, Culturable bacteria, Strain identification