Effect of combined culture methods on bacterial colony count in hemodialysis water and dialysate

Abstract

Objective To compare the detection ratio of bacterial colony count in dialysis water, dialysate and raw water with different media and different incubation conditions, searching for suitable methods to detect bacteria from dialysis water. Methods Between Jan 2012 and Dec 2012, 176 samples of hemodialysis water and dialysate, 88 samples of raw water were collected by hemodialysis unit, Renji hospital. Samples were inoculated in duplicate on spread plates with blood agar, Reasoner's 2A(R2A), tryptone glucose extract agar(TGEA) respectively, at different temperature and time. After incubation, the numbers of colonies were quantified. Results The bacterial colony counts in dialysis water, dialysate and raw water were the lowest in blood agar and the difference had statistical significance with R2A or TGEA culture media (P<0.01). The detection rate of dialysis water and dialysate were 61.9% in R2A at 20℃ for 168 hours. According to the standard of the association for the advancement of medical instrumentation(AAMI), the detection rate had no difference among these media with different conditions. Combined with medium of R2A and TGEA, the detection rate of bacteria was 77.6% at 20℃ for 168 hours and the bacteria detection rate was significantly increased than that in culture R2A and TGEA under the same conditions (77.6% vs 61.9%, 50.6%, P value was 0.003 and 0.001). Conclusions The method of R2A or TGEA agar culture can improve the detection rate of bacterial colony count compared with the method of blood agar. The method of R2A combined with TGEA at 20℃ for 168 hours can improve the detection rate of bacteria in dialysis water and dialysate. Key words: Hemodialysis; Dialysis solutions; Culture techniques; Bacterial culture; Dialysis water; Culture medium