| Antibiotic-resistant bacteria are abroad present and transmitted in water environment, which is an enormous threat to human beings. Various kinds of wastewater are collected into municipal wastewater treatment plant, which contain a great number of antibiotic-resistant bacteria. Although most of bacteria in wastewater can be removed by secondary treatment, occurrences and concentrations of antibiotic-resistant bacteria in the effluent is still considerable. Therefore, it has drawn much concern whether the discharge of secondary effluent put impact on antibiotic resistance and microbial community of receiving water. Chlorination is one of the most common wastewater disinfection technique, and the proportion of antibiotic-resistant bacteria is increasing or not after effective inactivation of bacteria by chlorination, which is the hot topic in recent years. In this study, the antibiotic resistances of bacteria in the Chanhe River, the Bahe River and the outlet of wastewater treatment plant nearby were investigated by molecular biological method and resistant phenotype analysis. In addition, characteristic of transconjugants with antibiotic resistance genes during the process of chlorination was studied, which provided the scientific basis for optimization of wastewater disinfection process and the control the transmission of antibiotic-resistant bacteria in urban water environment.Water samples were collected from eight sampling sites located in the Chanhe River and the Bahe River reaches and one outlet of wastewater treatment plant in Xi'an City. Using bacterial culture, PCR detection and denaturing gradient gel electrophoresis analysis technology, the antibiotic resistance rates of heterotrophic bacteria, tetracycline resistance genes and microbial community structure in urban river were investigated. The results showed that the average resistance rates of heterotrophic bacteria in various water samples from the Chanhe River and the Bahe River to sulfamethoxazole, tetracycline, ciprofloxacin and cefotaxime were 18.3%, 6.2%, 2.7% and 6.2% respectively. The order of resistance rates of heterotrophic bacteria in urban river samples to four kinds of antibiotics was the same as that in the effluent discharged from wastewater treatment plant. There was no significant correlation between heterotrophic bacteria concentrations and their resistance rates in the urban river. Compared with the upper reaches of urban river, the concentration of heterotrophic bacteria in the lower reaches from wastewater treatment plant outlet did not increase significantly, while their resistance rate to several antibiotics was increased. The main resistance genes to tetracycline were tetA(100% detection rate) and tetB(75% detection rate), showing that the tetracycline resistance of heterotrophic bacteria in the urban rivers could be realized by alternations of efflux-pump. The discharge of effluent caused the disappearance of some sensitive species and the increase of pathogenic bacteria or opportunistic pathogens in the downstream river neighboring to the outlet of wastewater treatment plant.Making the multiply antibiotic resistant Salmonella strains isolated from wastewater treatment plant as donor and Escherichia coli NK5449 as receptor, the conjugation experiments were carried out. The antibiotic resistances of transconjugants to 9 kinds of antibiotics were analyzed by Kirby-Baner disc agar diffusion method, and the plasmids were extracted from transconjugants by alkaline lysis method. The results were obtained as follows: 15 transconjugants were isolated from the conjugation experiments by filter mating method. The conjugantion rate was 41.7%, which indicated that part of multiply antibiotic resistant Salmonella strains had the ability to spread mobile elements to other different species. All 15 transconjugants carried conjugative plasmid and 14 of them were resistant to tetracycline, sulfamethoxazole, ampicillin, chloromycetin, streptomycin. The resistance pattern of transconjugants had certain links with donator strains.Study on the inactivation and reactivation of conA4 and NK5449 by chlorination were carried out by simulation experiments. The results showed that the inactivation of conA4 and NK5449 were 5.3-log and5.2-log, respectively at the available chlorine dosage of 1mg/L for 8 min. There was no significant difference between the inactivation of conA4 and NK5449 when the concentration of available chlorine was 1mg/L. At a constant CT value of 8mg·min/L, the inactivation of conA4 and NK5449 at high available chlorine dosage with short contact time was more effective than that low available chlorine dosage with long contact time. Transcongugant conA4 became to be sensitive to tetracycline, sulfamethoxazole and chloromycetin, while be resistant to gentamicin after chlorination. Adding sodium thiosulfate after the CT of 8mg·min/L, the resistance pattern of con A4 to six antibiotics didn't change after 48 h of reactivation, which was similar to that CT of 16mg·min/L. There was no significant difference of the inhibition zone diameters to six antibiotics between the reactivation of conA4 after 8mg·min/L and 16mg·min/L of chlorination. |
PDF Full Text Request