Pathogenic Bacteria Pollution Characteristic Of Typical Surface Water In Xi'an City

In order to make clear the pathogenic bacteria pollution characteristic of the surface water in the urban and suburb area of Xi'an city, we carefully chose five typical water body including 2 rivers, one of which is the source for urban water supply, 2 lakes and 1 secondary effluent of a domestic wastewater treatment plant. Samples were collected periodically and consecutively three times each month with the detection method covered both traditional cell culture technique and the quantitative polymerase chain reaction (QPCR) technique. Escherichia coli and fecal coliform were chosen as the indicator of fecal pollution with total bacterial as reference. The counts of these bacteria's colony-forming units (CFU) were compared with measurements by QPCR method established by this study. The QPCR results were supposed as the indicator of other pathogenic bacteria pollution in water.For the QPCR method, we introduced a universal primer with Shigella dysenteriae, Vibrio cholerae, Salmonella typhrmurium, and Escherichia coli. as the reference strains. The universal primer was designed and synthesized according to the high conversation of 16S rRNA gene. Combined with QPCR technique, we make the sensibility of this new method up to 25cfu/100mL. What's more, the accurate and sensitive measurements of these organisms can be obtained within several hours.Regression analyses and statistical comparisons of the MF culture and QPCR results showed that a positive correlation between the QPCR and Escherichia coli. with a strong correlation coefficient (r=0.93) can be seen. Besides, the QPCR results averaged 2.2-5 fold higher than the Escherichia coli. counts and 16-34fold higher than fecal coliform.Regarding different water samples, Heihe River of high quality as source water reached the Grade I surface water standard and was also quite safe according to QPCR results; Beihu Lake and Xingqinghu Lake could reach the Grade II or Grade III surface water quality standard, but there were higher health risk during the holidays when more people came for entertainment; Although Chanhe River receives industrial discharge, the fecal coliform counts were not very high, however, a very high QPCR may indicate the existence of large numbers of other pathogenic bacteria in the industrial discharge. The secondary effluent without disinfection was of high concentration of fecal coliform and much higher concentration of other pathogenic bacteria according to QPCR results.The current guidelines, based on MF results were unlikely to be applicable to QPCR results. More statistic documents should be collected to make a new guideline.