Detection Of Antimicrobial Resistance And Integrons Among Clinical Isolates Of Shigella Collected From Several Hospitals Of Anhui Province

ObjectiveTo investigate the resistance of153clinical isolates of Shigella spp. against21antimicrobials collected from Anhui province.To investigate distribution of integron and gene cassettes embedded in153clinicalShigella isolates and analyze the resistance of the integron positive Shigella isolates.Materials and MethodsThe153clinical isolates of Shigella spp. were collected between2007and2010from31hospitals of Anhui province. All isolates were cultured according to national guide toclinical laboratory procedures and were identified with the Microscan Walkaway-96System and serological identification.Antimicrobial susceptibility testing was performed by agar dilution method. E. coliATCC25922was stored at the Anhui Center for Surveillance of Bacterial Resistance(Hefei, Anhui, China).PCR were carried out to detected IntI gene and gene cassettes in all Shigella isolates.Conjugation experiments and Southernblot were carried out to investigate the genomicposition of integrons in Shigella isolates. To analyze the relationship between integrons and antimicrobial resistance in clinicalisolates of Shigella.ResultsIn153clinical Shigella isolates,132isolates (86.3%) were S flexneri,19isolates(12.4%) were S sonnei, and2isolates (1.3%) were S dysentery.All isolates were susceptible to imipenem. The resistance rates to cefoxitin, ceftazidim,cefepime, piperacillin/tazobactam, levofloxacin and gatifloxacin were low, and theresistance rates were under12.0%. Shigella isolates were no longer susceptible toampicillin, nalidixic acid, tetracycline, chloramphenicol andtrimethoprim/sulphamethoxazole and the resistance rates were above75.0%. Theincidence of multi-drug resistance even reached up to94.8%.Most Shigella isolates (144/153,94.1%) were found to harbor one or two classes ofintegrons (Table3):133isolates possessed a class1integron (86.9%) including22typical class1integron and120atypical class1integron,109isolates possessed a class2integron (71.2%), and class1integron coexisted with class2integron in98isolates.Of the133intI1positive isolates, only22isolates were positive for the PCR detectionof the variable region of typical class1integron with the primer pair In1-F-In1-R. Thegene cassettes of typical class1integrons dfrA17-aadA5, aar-3-aacA4anddfrA12-orfF-aadA2were detected in19isolates,2isolates and1isolates, respectively;120isolates were detected to contain gene cassette arrays of blaOXA-30-aadA1with theprimer pair intIca-IS1. IntI2was amplified in109Shigella isolates and all containedconstant gene cassette arrays of dfrA1-sat1-aadA1, while intI3was not found. Conjugation experiments and Southern blot confirmed that typical class1integronlocated on5.1kb plasmid. Atypical class1integron and class2integron did not locateon plasmid.The resistance rates to PIP, CTX, CFP, ATM, GM, LVX, GAT and NFXL in typicalclass1integron positive Shigella isolates were significantly higher than negativeisolates. The resistance rates to AMP TET CHL in atypical class1integron positiveShigella isolates were significantly higher than negative isolates. The resistance rates toAMP, PIP, CTX, CRO, ATM, GM, TET and SMZ in class2integron positive Shigellaisolates were significantly higher than negative isolates.ConclusionsThe main serotypes of Shigella isolates in Anhui province were S flexneri, followed byS sonnei and S dysentery. Shigella isolates showed high resistance to severalantimicrobials and multidrug resistance is fairly serious. Cefoxitin, ceftazidim, cefepime,piperacillin/tazobactam, levofloxacin and imipenem can be used in treating patientsinfected with Shigella as empirical therapy in our region. The existence of integronsplays an important role in drug resistance.