The Effect Of Freeze-thaw Cycles On The Survival Of The Common Intestinal Bacteria In The Natural Water Of The Second Songhua River(Jilin-Songyuan Section)

With the development of livestock and poultry breeding,pathogenic microorganisms Enterobacteriaceae went into the surface water with sewage discharge and mass stack of livestock manure,which did great harm to human and livestock health.Such adverse effects that pathogenic microorganism did to human are related to its survival law.Survival of microorganism in water is relative to water physical and chemical properties,water material composition and climate.Some researches studied the relation between survival of microorganism and water physical and chemical properties and water material composition,however,less studied the relation between climate and survival of microorganism,especially relation between survival of microorganism and water physical and chemical properties and material composition under freeze-thaw cycles.It’s an important content of microorganism’s survival.Thus it’s necessary to study this part,not only can this research reveals the survival law of microorganism in river of northern China,but also it can provide theoretical basis for pollution prevention of microorganism in river and protection of human health.Hence,this paper adopted the combination method of indoor simulation experiments and Weibull model,took unfrozen condition as control,studied the relation between survival law of Escherichia coli(Ec10538),Salmonella enterica(sd-51)and Enterobacter cloacae(Ec7256)and physical-chemical properties and material composition of water.On this basis,single factor experimental method and Weibull method were combined to further investigate the relation between survival of these three strains of bacteria and water material composition and its concentration.Ultimately,variation of pH,EC,SOD and CAT enzyme activity in freezing-thawing system were compared with unfrozen system,and reasons of E.coli cells damage which caused by freeze-thaw cycles were investigated.Results are as follows.(1)Survival experiments of these three strains of bacteria in 12 kinds of water samples showed that impelled by freeze-thaw cycles,survival amount of Ec10538,sd-51 and Ec7256 decreased significantly,and their survival law in water were changed,such changes were relative to water physical-chemical properties and material composition.In freeze-thaw cycles,survival fitting time of these three strains in water were negatively correlated with concentration of TOC,Na+,K+,Ca2+,SO42-,NO3-,Mg2+,F-,TP and EC values,significantly.However,survival fitting time was less affected by pH and concentration of Fe3+ and Cl-.In addition,survival law of Ec10538,sd-51 and Ec7256 in river water were greatly influenced by water quality,and survival of these three strains in water which are not over-standard were superior to that in over-standard water.(2)Results of single factor experiment of Ec10538 showed that all metal cation presented effect of survival inhibition,effect of K+ and Ca2+ inhibition was relative to its concentration,however,ionic and complex iron was independent of concentration;Cl-showed effect of facilitation to survival of Ec10538,other anions showed effect of inhibition,effect that Cl-,SO42-and NO3-presented was relative to concentration,effect that F presented was not significantly relative to concentration;glucose,sucrose and fulvic acid showed inhibition to survival of Ec10538,and effect of concentration was not significant;acetic acid and lactic acid showed facilitation to survival of Ec10538,and effect of facilitation was enhanced with the increase of concentration.Results of single factor experiment of sd-51 showed that all metal cation presented effect of survival inhibition,and relationship between effect of survival inhibition and concentration was in accordance with Ec10538;all anions showed effect of inhibition,and inhibition of Cl-,SO42-was related to concentration,influence of NO3-and F-concentration was not significant;fulvic acid showed inhibition to survival of sd-51,other organic carbon all showed facilitation and when its concentration was bigger,survival time of sd-51 was longer.Results of single factor experiment of Ec7256 showed that all metal cation presented effect of survival inhibition,inhibition of iron and Ca2+ was enhanced with concentration increasing,inhibition of K+ was irrelevant to concentration;Cl-promoted survival of Ec7256,other anions presented inhibition,and effect of four anions concentration was not significant;effect of organic carbon to Ec7256 was similar to sd-51.Fitting results showed that acetic acid and lactic acid could extend survival time of Ec7256;glucose,sucrose,acetic acid,lactic acid and Cl" could extend survival time of sd-51 and Ec7256.(3)Over time,EC increased in water sample which added bacteria in unfrozen condition,however,EC first increased and then decreased in water sample which added bacteria in freeze-thaw cycles.No matter in freeze-thaw cycles or unfrozen condition,pH of water sample which added bacteria are stable and had no regular changes.In freeze-thaw and unfrozen condition,SOD and CAT activity in water sample which added bacteria all increased,and SOD activity increased greater than CAT activity,final activity of SOD and CAT in freeze-thaw cycles was larger than that in unfrozen condition.