| The increasing and dissemination of antibiotic-resistant pathogenic bacteria havebecome a health problem all over the world, and the abuse of antibiotics in livestockand poultry breeding industry is making the problem more acute. Municipal wastewatertreatment system is an integral part of the modern city, which provides favorableconditions for the growth of resistance bacteria. Recent studies, focusing on bacteriarelated to indigenous bacteria or indicator bacteria, rarely involved pathogens bacteria.Salmonella is a typical intestinal pathogenic bacteria, which cause a variety of humandiseases.Therefore, it is urgent to carry out research on antibiotic resistance ofSalmonella, which is significant to control the spread of resistant bacteria.This studygave a systematic analysis on the distribution of antibiotic resistance of Salmonella tocommon antibiotics, and antibiotic resistance genes and integrons in antibiotic-resistantSalmonella in municipal wastewater plants. The study can be divided into followingthree parts:(1)In order to reveal the presence and distribution of antibiotic-resistant Salmonellain municipal wastewater plant,280Salmonella strains were isolated from municipalwastewater treatment plant (WWTP) A，D and E(A2/O process) and WWTP H (Orbaloxidation ditch) by bacteria separating culture and polymerase chain reactionmethod.The analysis of antibiotic resistance to9kinds of common antibiotics in theseisolates was conducted by Kirby-Baner disc agar diffusion method. The results areobtained as follows:Tetracycline and sulfamethoxazole showed the highest percentage of resistantstrains from four municipal wastewater treatment plants.The resistance rate to tetracycline and sulfamethoxazole in WWTP A，D and E were47.5%and38.5%，andthose in WWTP H were39%and32.2%,respectively.In the WWTP A、 D and E,12.7%were resistant to single antibiotic,24%to two antibiotics and19.4%to multipleantibiotics,and the infrequent resistance patterns were observed for ampicillin andtetracycline-sulfamethoxazole-chloramphenicol–streptomycin-ampicillin-gentamicin.The single, double, and multiple resistant rate in WWTP H were17%,6.8%and5.8%, andthe resistance pattern was relatively disperse. There was some change in AntibioticResistance Index (ARI) of Salmonella for different units of wastewater treatment plants.In WWTP A，D and E，the ARI of Salmonella in secondary effluent after chlorinationwas high than that in other units.(2)The distribution of tetA, tetB, sul1, sul2and sul3in antibiotic resistantSalmonella from municipal wastewater plantA，D and E were investigated by PCRmethod. TetA was the major genotype of tetracycline resistance genes,the detectionfrequency of tetA was81%. Sul1, sul2and sul3were main genotypes ofsulfamethoxazole resistance genes, the detection frequencies of those ARGs were over40%. The genes tetA and sul3were frequently detected in antibiotic resistantSalmonella in raw wastewater, while the distribution of antibiotic resistance genes inSalmonella changed significantly after wastewater treatment process. The detectionfrequencies of tetA,sul1,sul2were higher in the secondary settling tank and the chlorinedisinfection tank after the A2/O process.(3)The distributions of class I integron in raw wastewater、the secondary settlingtank and the chlorine disinfection tank of municipal wastewater plant A，D and E wereinvestigated by PCR method. The results showed that:The detection frequencies of Int1and qacE Δ1-sul1in antibiotic resistanceSalmonella were significantly higher than that of sensitive strains, and the resistantspectrum in class I integron positive group were significantly wider than that in negativegroup, which showed that class I integron played a very important role in the resistanceof Salmonella. Int1gene significantly was associated with tetA, sul1, sul2and sul3gene(p<0.01), and qacEΔ1-sul1gene significantly associated with tetA, sul1and sul2gene (p<0.01), which showed that Int1and qacEΔ1-sul1played an important role inmediating the ARGs,and it was more reasonable to regeard Int1gene as standard of class I integron.The detection frequencies of Int1and qacEΔ1-sul1genes increased inthe secondary settling tank and the chlorine disinfection tank, which suggested thatsewage treatment and chlorine disinfection were likely to induce the emergence of classI integron. |
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