Chemotherapy with or without molecule-targeting agents is the primary choice for patients with unresectable metastatic coloreetal cancer. New treatment strategies like intermittent therapy and maintenance therapy may not inferior to treatment until progression or unacceptable toxicity in maintaining the benefit for patients who responded or had stable disease after the first-line therapy,and also can reduce the drug related side effeets and improve the quality of life.

Objective To study antimicrobial resistance of clinically isolated Escherichia coli (E.coli),the preva-lence of integrons in E.coli,and relation of integron with antimicrobial resistance of E.coli.Methods E.coli isola-ted from three hospitals of Guangdong Province from 2010 to 2012 were collected,and antimicrobial susceptibility testing was performed by Kirby-Bauer method;integrons were detected by polymerase chain reaction (PCR),and gene cassette was analyzed by sequencing.Results A total of 156 E.coli isolates were collected,antimicrobial sus-ceptibility testing showed that resistance rate of E.coli to most penicillins,cephalosporins,fluoroquinolones,amin-oglycosides and sulfonamides were over 50%;the resistance rate to antimicrobials < 10% included cefoperazone/sulbactam(0),imipenem(3.85%),cefotetan(4.35%),ertapenem(7.69%)and piperacillin /tazobactam (8.97%);The positive rate of class I integron was 57.69%(90/156);the positive rate of class I integron in multidrug-resist-ant and non-multidrug-resistant E.coli was 66.00% (66/100)and 64.71 % (22/34)respectively,the difference was not statistically different (P >0.05),but compared with sensitive E.coli (9.09%,2/22),the difference was statisti-cally different (P<0.01 ).There were nine types of integron-drug resistant gene cassettes in the variable regions, most of which contained aadA and dfrA.Conclusion Antimicrobial resistance of E.coli is serious;high incidence of class I integrons are widely found in E.coli,and is closely related with drug resistance of E.coli,class I integrons mainly mediated aminoglycosides,sulfonamides and beta-lactams resistance.