Comparison of techniques for culture of dialysis water and fluid

Potentially pathogenic culturable bacteria in hemodialysis waters

BACKGROUND

Hemodialysis patients are at risk of acquiring healthcare-related infections due to using non-sterile water to prepare hemodialysis fluid. Therefore, microbiological control and monitoring of used water are of crucial importance.

MATERIALS AND METHODS

In this work, we identified bacterial populations occupying a hemodialysis water distribution system for almost a 6-month period in Ahvaz city, southwest of Iran. A total of 18 samples from three points were collected. We found high colony counts of bacteria on R2A agar. 31 bacteria with different morphological and biochemical characteristics were identified by molecular-genetic methods based on 16 S rRNA gene sequencing. Endotoxin concentrations were measured, using Endosafe® Rapid LAL Single-Test Vials.

RESULTS

A diverse bacterial community was identified, containing predominantly Gram-negative bacilli. The most frequently isolated genus was Sphingomonas. Five species including M. fortuitum, M. lentiflavum, M.szulgai, M. barrassiae, and M. gordonae was identified .Despite the presence of Gram-negative bacteria the endotoxin analysis of all samples revealed that their endotoxin values were below the detection limit.

CONCLUSION

The members of Sphingomonas genus along with Bosea and mycobacteria could be regarded as pioneers in surface colonization and biofilm creation. These bacteria with others like Pelomonas, Bradyrhizobium, staphylococcus, and Microbacterium may represent a potential health risk to patients under hemodialysis treatment.

Comparing the Effects of Two Culture Methods to Determine the Total Heterotrophic Bacterial Colony Count in Hospital Purified Water

BACKGROUND

Accurately detecting the quantity of microorganisms in hospital purified water is of significant importance for early identification of microbial contamination and reducing the occurrence of water-borne hospital infections. The choice of detection method is a prerequisite for ensuring accurate results. Traditional Plate Count Agar (PCA) belongs to a high-nutrient medium, and there may be limitations in terms of accuracy or sensitivity in detecting microorganisms in hospital purified water. On the other hand, Reasoner's 2A agar (R2A) has characteristics, such as low-nutrient levels, low cultivation temperature, and extended incubation time, providing advantages in promoting the growth of aquatic microorganisms. This study, through comparing the differences in total colony counts between two detection methods, aims to select the method more suitable for the growth of aquatic microorganisms, offering new practical insights for accurately detecting the total count of heterotrophic bacteria in hospital purified water.

METHODS

The most commonly used plate count agar (PCA) method, and the R2A agar culture were adopted to detect microorganisms and determine the total number of bacterial colonies in the water for oral diagnosis and treatment water and terminal rinse water for endoscopes in medical institutions. The two water samples were inoculated by pour plate and membrane filtration methods, respectively. Using statistical methods including Spearman and Pearson correlation, Wilcoxon signed-rank sum test, paired-Chi-square test, and linear regression, we analyze the differences and associations in the bacterial counts cultivated through two different methods.

RESULTS

In 142 specimens of the water, the median and interquartile range of the heterotrophic bacterial colony number under the R2A culture method and under the PCA culture method were 200 (Q1-Q3: 25-18,000) and 6 (Q1-Q3: 0-3700). The total number of heterotrophic bacteria colonies cultured in R2A medium for 7 days was more than that cultured in PCA medium for 2 days (P < 0.05). The linear regression results showed a relatively strong linear correlation between the number of colonies cultured by the R2A method and that cultured by the PCA method (R2 = 0.7264). The number of bacterial species detected on R2A agar medium is greater than that on PCA agar medium.

CONCLUSION

The R2A culture method can better reflect the actual number of heterotrophic bacterial colonies in hospital purified water. After logarithmic transformation, the number of colonies cultured by the two methods showed a linear correlation.

Single-species (bacterial, fungal, or mycobacterial) biofilms or dual-species (mycobacterial-fungal) biofilms formed in dialysis fluids

Continuous hemodialysis system monitoring is necessary to prevent microorganism growth and health problems. This study evaluates single- and dual-species biofilm formation in microtiter plates by using dialysis solutions under aerobiosis or 5% CO₂ atmosphere. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, Candida parapsilosis sensu lato, and Mycobacterium smegmatis produce single-species biofilms in all dialysis solutions in both oxygenation conditions. Dual-species biofilm cultures grown at 5% CO₂ atmosphere and in dialysate containing glucose reveal that M. smegmatis benefits from its association with C. parapsilosis. The dialysate and its constituent solutions support the growth of all the mono-species and the inter-kingdom mycobacterial/yeast biofilms in both aerobiosis and microaerophilic conditions.

The importance of sampling technique and rinse water for assessing flexible gastrointestinal endoscope reprocessing: A 3-year study covering 59 centers

BACKGROUND

Various guidelines recommend several sampling techniques to verify endoscope reprocessing, but a comparative study of the efficiency for recovering microorganisms was rare. Our goal was to compare different sampling techniques for the postreprocessing endoscope to assess residual bacterial contamination and analysis of the critical factors affecting the endoscope reprocessing failure.

METHODS

From 2016 to 2018, 3 techniques, the conventional flushing sampling method, flush-brush-flush sampling method (FBFSM), and pump-assisted sampling method (PASM), were compared covering all 59 endoscope units in Tianjin, China.

RESULTS

A total of 237 (84.64%) flushing channel samples and 110 (61.11%) final rinse water samples met the Chinese national standard. The univariate analysis showed that the qualified rates of endoscope reprocessing sampled by PASM (65.52%) and FBFSM (75%) were significantly lower than those of the conventional flushing sampling method (91.38%). Five other factors, including the final rinse water, dry, and hospital level, were potential factors besides sample technique. The multivariate logistic analysis indicated only 2 factors (sampling technique and final rinse water) remained in the model. FBFSM, PASM, and the purified water were significantly associated with the odds of endoscope reprocessing failure, with the odds ratio (95% confidence interval) of which were 4.206 (1.757-10.067), 5.326 (2.463-11.645), and 0.309 (0.137-0.695), respectively.

CONCLUSIONS

The problem of residual microorganisms of the postreprocessing endoscope was severe. Sampling technique and final rinse water were critical for endoscope reprocessing verification.