Characterization Of The Enterobacter Antibiotic Resistance Pattern In Typical Water Environment Of Urbanization Area

With the widespread of antibiotics in medical care, animal husbandry andaquaculture, the problem of bacterial antibiotic resistance is causing increasingconcerns. In this study, a multi-scale diagnostics combining phenotype, genotypeand mobile gene elements is utilized to investigate the antibiotic resistance patern ofenterobacter in a typical urbanization area of Shenzhen.Water samples were collected from the GuangMing sewage plant influentsection, activated sludge segments and the downstream of MuDun River.270repesentative isolates was finally chosen from561waterborne isolates. Seven typesof antibiotics including chloramphenicol, tetracycline, gentamicin, sulfonamides,ciprofloxacin, cephalothin and ampicillin were chosen to test the susceptibility of270isolates. By analyzing bacteria resistance ratio and trends after sewagetreatment facilities, major antibiotics tested were divided into three categories. Suchclassification will help in providing the basis for the classification of the antibioticresistance pollution and management at different levels.The control to microbial resistance of sewage treatment facilities was reflectedin two aspects:(1) comparing to the sewage influent, the proportion of multi-drugresistant microorganisms decreased;(2) apart from the carbapenems, bacterialresistance to the majority antibiotics had decreased, such as chloramphenicolresistance fell from22%to7%, ciprofloxacin from10%to4%, sulfonamides from48%to34%and tetracycline decreasing from46%to36%. Thus the artificialtreatment facilities are an important barrier to control the resistance pollution inurbanization areas.Through the restriction fragment length polymorphism phynotyping (RFLP),270isolates were demonstrated to be mainly Klebsiella and Aeromonas. It should benoted that the resistance ratio of gentamicin for both isolated Klebsiella andAeromonas resistance strains even increased after the activated sludge treatmentfacilities. The gentamicin resistance dissemination mechanisms are worth furtherstudy.Through plasmid extraction and electrophoresis of resistant isolats, certaincorrespondence between bacterial resistance and the presence of plasmids weredemonstrated. Nearly all isolated strains with five or above types of antibioticsresistance carry plasmidsOne multi-resistant Klebsiella strain HITJ-05was found to carry a7700bpColE1plasmid pHITJ-5. The complete nucleotide sequencing, functional and evolutionary analysis of the plasmid demonstrated that a Tn501type transposon unitand potential virulence factor acyltransferases are encoded on this plasmid. Onechloramphenicol resistance gene cmlA was identified in preliminary shotgunsequencing of other plasmids mixture, indicating a potential mechanism for lateraltransfer of chloramphenicol resistance.