Studies On Epidemiology Of Bacteria Producing Extended Spectrum Beta-lactamases And Plasmid-mediated AmpC Beta-lactamases

ObjectiveThe epidemiology of both Escherichia coli and Klebsiella pneumoniae isolated from Tongji Hospital affiliated to Tongji Medical Collage of Huazhong University of Science and Technoligy was studied to establish bases for clinical usage of antimicrobial agents reasonablely and reducing the strains spread by describing the prevalence and antimicrobial resistance of strains producing extended spectrum beta-lactamases(ESBLs) and plasmid-mediated AmpC beta-lactamases(pAmpC), detection the genetypes of pAmpC.Methods468 strains of E. coli and 218 strains of K. pneumoniae were isolated from Tongji Hospital. The minimum inhibition concentration(MIC) of the clinical isolates to 15 kinds of antimicrobial agents was tested by agarose dilution method. The ESBLs producing strains were detected by standard disk diffusing test according to national committee of clinical laboratory standards (NCCLS). Plasmid-mediated AmpC beta-lactamases carriers were screened by improved three-dimensional test, and identified by multiplex polymerase chain reaction ( PCR) and sequencing method.ResultsThe isolated rates of ESBLs-producing strains in E. coli and K. pneumoniae were 32.7% (153/468) and 36.2% (79/218), respectively. All of E. coli and K. pneumoniae involved in this study were susceptible to imipenem.The resistance of non-ESBLs-producing E. coli to the second, the third and the fourth generation cephalosporins was from 10.2% to 32.7%, but the resistance of ESBLs- producing strains to the second generation cephalosporins was higher than 90% and from 30% to 55% to the third and fourth generation cephalosporins. The significance between ESBLs- and non ESBLs-producing strains was obviously (P<0.01). For ESBLs- producing E. coli strains, the resistance to cefoxitin, aztreonam, amocillin/clavulanic acid, cefoperazone/sulbactam, gentamicin, ciprofloxacin was 53.6%, 44.6%, 42.9%, 40.4%, 73.3% and 83.0% respectively, which were higher than that of non-ESBLs- producing strains(P<0.01). The drug resistant rate to amikacin in ESBLs- producing strains was 12.5% ,which was higher than that of 2.7% in non ESBLs- producing strains (P<0.05). The resistance of ESBLs-producing and non- ESBLs-producing strains to tetracycline was above 70%. Compared with that of non-ESBLs- producing strains(8.2%), the resistance of ESBLs-producing strains to piperacillin/tazobactam was higher(12.5%) and there was no significance(P>0.05). For non-ESBLs- producing strains, the MIC50 and MIC90 of antimicrobial agents were in the range of susceptibility except amocillin/clavulanic acid and gentamicin. However, the MIC50 and MIC90 of ESBLs-producing strains to antimicrobial agents were in the range of resistance other than the MIC50 of ceftazidime and amikacin which were in range of susceptibility and intermediate.For ESBLs- producing K. pneumoniae strains, the resistance to the second generation cephalosporins (cefazolin, cefuroxime), the third generation cephalosporins (ceftazidime, cefotaxime) and the fourth generation cephalosporins (cefepime) was 100%, 97.6%, 41.0%, 61.0% and 23.4% respectively, which were higher than that of non-ESBLs- producing strains(14.3%, 28.6%, 4.8%, 14.3% and 4.8%), P<0.01. The resistance of ESBLs- producing strains to cefoxitin, aztreonam, amocillin/clavulanic acid, piperacillin/tazobactam , cefoperazone/sulbactam, gentamicin, amikacin, ciprofloxacin ,tetracycline was 58.5%, 70.7%, 55.1%, 26.8%, 40.3%, 54.5%, 63.6% and 60.9% , respectively, which were higher than that of non ESBLs- producing strains(28.6%, 9.5%, 13.3%, 4.8%, 9.5%, 27.3%, 20.6%, 38.5%), P<0.01. The resistance of ESBLs- producing strains to amikacin was 28.8% , which was higher than that of non ESBLs- producing strains (14.3% )(P<0.05). Except cefazolin and tetracycline, the MIC50 and MIC90 of non-ESBLs- producing strains to other antimicrobial agents were in the range of susceptibility. All of MIC50 and MIC90 of ESBLs-producing strains to antimicrobial agents were in the range of resistance.Six strains of AmpC beta-lactamase-producing E. coli and thirteen strains of AmpC beta-lactamase-producing K. pneumoniae were screened by improved three-dimensional test. The positive rates were 1.28%(6/468) and 5.96% (13/218) respectively.Seven strains of K. pneumoniae harboring DHA-1 type plasmid-mediated AmpC beta-lactamase were detected by multiplex PCR and sequencing. The positive rate was 3.2% (7/218).All of the seven pAmpC-producing strains were resistant to Cefoxitin, Cefazolin, Cefuroxime, Amocillin/clavulanic acid and gentamicin, but susceptible to Imipenem. Three of them were susceptible to cefepime. ConclusionThe isolated rates of ESBLs-producing strains among E. coli and K. pneumoniae in Tongji hospital were 32.7% (153/468) and 36.2% (79/218), respectively.Except to ciprofloxacin, the resistance of non -ESBLs -producing strains to other common antimicrobial agents was less than 30%, While the resistance of ESBLs- producing strains to antimicrobial agents were more than 40% exceptpiperacillin/tazobactam and amikacin (<30%). No strains were found to resistant to imipenem in this study.The positive rates of AmpC beta-lactamase- producing strains in E. coli and K. pneumoniae by improved three-dimensional test were 1.28% (6/468) and 5.96%(13/218) respectively.DHA-1 plasmid-mediated AmpC beta-lactamase were detected in seven pAmpC-producing K. pneumoniae strains by multiplex polymerase chain reaction and sequencing in this study.The pAmpC-producing strains revealed high resistance. Only three of them were susceptible to cefepime. However, all of the seven strains were susceptible to Imipenem.