Study On Antibiotic Resistance Of Fecal Coliforms And Influencing Factors In Municipal Wastewater And Surface Waters

The widespread appearance of antibiotic-resistant bacteria (ARB) poses greatthreat to human health. Water is an important medium for the spread of bacteria.Understanding of urban water pollution condition of antibiotic-resistant bacteria hasgreat significance for the control of the health risks caused by the spread ofantibiotic-resistant bacteria in urban water environment related to human life. As atypical water hygiene indicator, fecal coliforms can better indicate the fecalcontamination from human and other warm-blooded animals. In these polluted waters,the concentrations of fecal coliforms are often high, which may reflect the overallresistance of bacteria to some extent.In this study, the antibiotic resistances of fecalcoliforms in municipal wastewater and surface waters in Xi’an city were investigated bybiochemical analysis and molecular biology techniques, which provided the scientificbasis for the control of antibiotic-resistant bacteria in urban water environment.Through the sampling in the three municipal wastewater treatment plants（WWTPs） located in Xi’an city, the antibiotic resistance of fecal coliforms to eightkinds of antibiotics including tetracycline (TET), ampicillin (AMP), chloramphenicol(CHL), streptomycin sulfate (STP), norfloxacin (NOR), ciprofloxacin (CIP), gentamicin(GEN) and cefotaxime (CTX) were investigated. In addition, the concentration of fecalcoliforms and their antibiotic resistance in urban lakes and rivers were also analyzed. Itwas found that the concentrations of fecal coliforms in the influents of these WWTPswere2.8×107CFU/L~9.3×107CFU/L. In municipal wastewater, the fecal coliformswere mainly resistant to AMP and CIP, in the influents and outfluents of municipalwastewater treatment plants, the AMP-resistant rates and CIP-resistant were19.2%~ 72.1%and24.4%~85.6%respectively. CTX-resiatant rate was the lowest, which were0~1.1%. In each process, the fecal coliforms′resistance showed no specific trends. InXingQingHu, south lake, ChanHe, BaHe, the concentrations of fecal coliforms in thesurface waters were1.6×103CFU/L~3.4×105CFU/L. In Surface waters, the fecalcoliforms were mainly resistant to AMP and CIP, which were14.3%~52.5%and15.2%~64.2%, CHL-resistant rates were the lowest, which were0~3.6%.The antibiotic sensitivity analysis using K-B disc agar diffusion method wasconducted to determine the antibiotic resistance phenotype of water environmentalisolates. The results showed that50strains were resistant to three or more antibiotics in57isolates. In21strains isolated from the WWTP-C wastewater treatment plant and36strains isaolated from WWTP-D, the sulfamethoxazole-resistant rates were90.5%and50%, respectively. From the secondary settling tank effluents of WWTP-D, we obtained5isolates, in which11kinds of tetracyclic resistance genes、4kinds of sulfonamideresistance genes and the5kinds of β-lactam resistant genes were detected by PCR.Among them,4kinds of tetracycline resistance genes including tetA, tetB, tetC and tetK,only1kinds of sulfonamide resistance gene(sul2) and3kinds of β-lactam resistantgenes(CMY2, TEM and CTX-MU) were detected.Through the simulations, we studied the effect of SBR process, chlorination andultraviolet disinfection on the TET-, AMP-, CIP-, CHL-resistance of fecal coliforms.The results showed that the antibiotic-resistant rates of fecal coliforms didn’t have nosignificant change after treated by SBR process, but which were a visible reduction inthe anoxic-stir phase. Chlorination and ultraviolet disinfection could effectivelyremoved most of fecal coliforms, while the change in dosage of disinfectants had asignificant impact on antibiotic resistance of fecal coliforms. In Chlorine disinfection,when the available chlorine concentration was from0to0.5mg/L, the fecal coliformsresistance rate to AMP, CIP and CHL all had different degrees of growth, whileTET-resistant rate showed downward trend; After chlorination with1.0mg/L availablechlorine, the resistance rate to AMP, TET, CIP and CHL was35.1%,5.6%,62.3%and0. In addition, about5h after chlorine disinfection, fecal coliforms resistance rate toAMP, CIP and CHL fell to the lowest, namely0; about24h after chlorine disinfection,the fecal coliforms resistance rate to TET, AMP and CIP reached a peak, then there were different degrees of reduction. After48h, it found that the fecal coliforms resistancerate to TET, AMP and CIP was59.4%,15.6%and67.7%respectively, compared withthe corresponding resistance without disinfect, which appeared to rise.During theUltraviolet disinfection processing, when ultraviolet irradiation doses increased range inabout0~16mJ/cm2, the fecal coliforms resistance rate to AMP, TET, CIP and CHL hadthe trend of decline, at about16mJ/cm2, which were15.0%,27.6%,34.7%and4.2%respectively; with the increase of the ultraviolet irradiation dose, the fecal coliformsresistance rate to the4kinds of antibiotics presented ascendant trend, which reached apeak in about22mJ/cm2;then the ultraviolet irradiation dose increased,the fecalcoliforms resistance rate to the4kinds of antibiotics decreased or leveled off.