Investigation Of Legionella Exposure In Secondary Water Supply In A Northern City And Analysis Of Influencing Factors

ObjectiveExplore the enzyme-substrate method suitable for the detection of Legionella pneumophila in drinking water,then apply this method to investigate the pollution level of Legionella pneumophila in the secondary water supply of a northern city and analyze the main influencing factors of the pollution level of Legionella pneumophila,to provide a scientific basis for preventing and controlling the outbreak of Legionella.MethodsThis study systematically investigated the feasibility of the enzyme substrate detection method for the detection of Legionella pneumophila in drinking water.We explore the effects of different culture temperatures and times on the detection results of the enzyme substrate method through experiments,and then determine the most suitable culture conditions.We performed a qualitative and quantitative comparison between the enzyme-substrate method and the isolation culture method through the spiked comparison test,and then used the enzyme-substrate method to detect Legionella pneumophila in drinking water samples,and used serotyping and 16S rDNA sequence analysis to confirm the results,to evaluate the accuracy of the results of the enzyme substrate method.After determining the detection method,we conducted a comprehensive and systematic investigation of the basic conditions and water quality indicators of the secondary water supply facility in a northern city,such as temperature,pH,disinfectant margin,turbidity,conductivity,total number of colonies,and the level of Legionella pneumophila,and then used Chi-square test and Logistic regression analysis to analyze and study the factors that may affect the growth of Legionella pneumophila in the secondary water supply.Results(1)Method research:The most suitable culture condition for the detection method of Legionella pneumophila enzyme substrate is 39℃ for 7 days.Under these conditions,the standard addition test showed that the recovery rate of Legionella pneumophila was 98.4%～108.8%;The comparison test results of the enzyme substrate method and the separation culture method showed that the qualitative results of the two methods were consistent(P>0.05),and the quantitative results had a significant positive correlation(Pearson correlation coefficient is 0.844,P<0.001);Use the enzyme substrate method to detect Legionella pneumophila in 48 drinking water samples.We detected 4 positive water samples and obtained 4 strains after isolation and culture.The serotypes were identified as Type 1,Type 7,Type 10,Type 15 Legionella pneumophila strains,and the results of 16S rDNA gene sequencing analysis showed two genotypes;(2)Investigation research:This study investigated a total of 304 sets of secondary water supply facilities in a northern city.The results showed that the detection rate of Legionella pneumophila was 16.45%(50/304),and the detection concentration of positive water samples ranged from 1.0 to>2272.6 MPN/100mL(the upper limit of detection is 2272.6 MPN/100mL),of which the detected concentration of 4 positive water samples exceeds the upper limit of method detection.The statistical analysis results show that the total number of colonies(P=0.001)and the remaining amount of disinfectant(P=0.032)are the main factors affecting the pollution of the secondary water supply by Legionella pneumophila.In addition,the long-term operation of equipment and office buildings also have a certain impact on the pollution level of Legionella pneumophila in the secondary water supply.Conclusion(1)The most suitable culture condition for the enzyme substrate method to detect Legionella pneumophila in drinking water is 39℃ constant temperature culture for 7 days.Compared with the isolation culture method,the detection results of these two methods have strong consistency.And it has the advantages of simple operation,high sensitivity,easy to read results,etc.,and can be used to detect Legionella pneumophila in drinking water.(2)Legionella pneumophila pollution exists in the northern city secondary water supply.The increase in the total number of bacterial colonies,the long operating life of equipment and office buildings may increase the risk of contamination by Legionell.a pneumophila in the secondary water supply system,and the increase in disinfectant balance can reduce the risk of contamination by Legionella pneumophila in the secondary water supply system.