ABSTRACT
Objective To investigate the molecular types of carbapenem-non-susceptible Esche-richia coli ( E.coli) isolates and their mechanism of carbapenem resistance .Methods Twenty-two carbap-enem-non-susceptible E.coli strains were isolated from 3 hospitals in Hangzhou from 2007 to 2011.The mini-mum inhibitory concentrations ( MICs) of antimicrobials to those isolates were determined by agar dilution method and E-test.The molecular mechanisms of carbapenem resistance of E.coli isolates were analyzed by conjugation experiment,PCR and DNA sequencing.Pulsed-field gel electrophoresis (PFGE),multilocus se-quence typing ( MLST ) , and phylogenetic typing were performed to analyze the molecular epidemiology of those isolates.Results The MICs of imipenem and meropenem to 22 E.coli isolates were ranged from 1 μg/ml to 16 μg/ml,and the MICs of ertapenem were 2 μg/ml to 64 μg/ml.All E.coli isolates produced the KPC-2 carbapenemase and various β-lactamases , and some of them also produced plasmid-mediated AmpC enzymes.Carbapenem resistance was transferred by conjugation and transformation from 22 E.coli iso-lates to E.coli EC600 strains.The E.coli transconjugants or transformants acquired the blaKPC-2 gene and showed similar antibiotic susceptibility patterns in comparison with donor strains .Only a few isolates were in-distinguishable or closely related as indicated by PFGE .Four sequence types including ST131 (9 isolates), ST648 (5 isolates),ST38 (2 isolates) and ST405 (2 isolates) were identified by MLST.Phylogenetic analy-sis indicated that 9 ST131 isolates belonged to phylogenetic group B 2 and the other isolates belonged to group D (11 isolates),group B1 (1 isolate) and group A (1 isolate),respectively.Conclusion The sequence type of prevalent E.coli isolates producing KPC-2 from Hangzhou was ST131,which is an international epi-demic,multidrug-resistant clone,followed by ST648.
ABSTRACT
Objective To investigate the resistant mechanism of Streptococcus pyogenes to ciprofloxacin and its homology.Methods Forty-eight isolates of Streptococcus pyogenes were collected from patients diagnosed with scarflet fever in districts of Beijing in March,2012 and MIC to ciprofloxacin and other 7 common antibiotics in clinic were detected by using blood M-H agar dilution method.Thirteen isolates,which have MICs≥4 mg/L against ciprofloxacin,were detected for mutations of Fluoroquinolone resistance genes gyrA,gyrB,parC,parE.At the same time,4 isolates,with MIC ≤ 0.25 mg/L against ciprofloxacin,were used for comparison.Homology analysis of 17 isolates from different areas of Beijing was performed by using the method of pulsed field gel electrophoresis.Results Sensitive rates of Streptococcus pyogenes to levofloxacin,ampicillin and penicillin were all 100％.The resistance rates to tetracycline,erythromycin and clindamycin were 91.7％ (44/48),91.7％ (44/48) and 89.6％ (43/48),respectively.MIC50 of ciprofloxacin,levofloxacin and moxifloxacin was 2 mg/L,1 mg/L and ≤ 0.25 mg/L,respectively ; MIC90 was 4 mg/L,2 mg/L and 0.5 mg/L,respectively.Of the 48 isolates of Streptococcus pyogenes,12 isolates showed the MIC at 4 mg/L,while one isolate has a MIC against ciprofloxacin at 8 mg/L,which isolated from Chaoyang district.Analysis of sequence of chromosome mediated fluoroquinolone resistance genes in those 13 ciprofloxacin non-susceptible isolates exhibited that there were 12 isolates that harbored Ser79Phe/Tyr mutation and 10 isolates harbored Ala121Val in parC gene.It is shown that one isolate contained Ser79Phe mutation in parC gene in the occurring of Ser371Leu mutation in parE gene for the first time,but there was no marked increase in ciprofloxacin MIC (MIC =4 mg/L).There were no mutations in gyrA and gyrB genes.The PFGE results demonstrated that the 17 tested isolates could be divided into 7 clones.The clone A isolates from Chaoyang,Daxing,Fengtai,Shunyi and Shijingshan district have a MIC ≥ 4 mg/L against ciprofloxacin,which covered 69.2％ of all MIC ≥4 mg/L isolates.The clone C isolates from Huairou district were MIC ≥4 mg/L isolates.B,D,E,F and G clones isolates come from different districts.Conclusions The mutation of parC gene was the main reason that contribute to the slightly increase of ciprofloxacin MIC in Streptococcus pyogenes isolated from Beijing.The PFGE analysis showed that there was a small scale prevalence caused by the infection of Streptococcus pyogenes in some districts.