Quinolone Susceptibility Analysis And Resistance Mechanisms For Streptococcus Agalactiae And S.Pyogenes

Objective:To investigate the antimicrobial susceptibility and mechanisms for quinolones of Streptococcus agalactiae from Taiwan and Zhejiang Province, to provide theoretical basis for clinical rational use of antimicrobial agents.Methods:The clinical isolates were identified by Vitek2Compact automated microbiology system, and then confirmed by Matrix-Assisted Laser Desorption/IonizationTime of Flight Mass Spectrometry (MALDI-TOF MS). Antibiotic susceptibilities were determined by Vitek2Compact automated microbiology system. Susceptibilities rates of9antibiotics for isolates from Taiwan and Zhejiang were analyzed by chi square test and fisher’s exact test. Antimicrobial resistance genes of quinolones in S. agalactiae such as parC and gyrA were investigated by PCRs and DNA analysis.Results:Sixty S. agalactiae strains were collected,30strains were from Taiwan and30 strains from Zhejiang. Of which45were from the normal examination of maternal and women’s vagina and vaginal fornix secretion samples,7cases of amniotic fluid from maternal,2cases from the semen,6from urine. Susceptibilities rates for penicillin of Taiwan and Zhejiang were96.7%and100%, those for cefepime were86.7%and93.3%, those for erythromycin were13.3%, and those for levofloxacin were70.0%. There were no statistical significance between susceptibilities rates of Taiwan and Zhejiang. Amine acid substitutions were detected in par C and gyrA genes in14of18levofloxacin-non-susceptible isolates. The predominant mutation type was the combination of Ser79Tyr and Ser81Leu mutation in parC and gyrA genes.Conclusions:The susceptibilities rates for common antibiotics of S. agalactiae from Taiwan and Zhejiang were similar. Ser79Tyr and Ser81Leu mutation were the main types in parC and gyrA genes in both of Taiwan and Zhejiang. Objective:To investigate the antimicrobial susceptibility and mechanisms for quinolones of Streptococcus pyogene and to analysis the homology of the strains.Methods:The clinical isolates were identified by API20Strep identification system, and then confirmed by Matrix-Assisted Laser Desorption/IonizationTime of Flight Mass Spectrometry (MALDI-TOF MS). Minimum inhibitory concentration (MIC) to ciprofloxacin and other7common antibiotics in clinic were detected by using blood M-H agar dilution method. Isolates of MICs>4mg/L against ciprofloxacin were detected for mutations of Fluoroquinolone resistance genes such as gyrA, gyrB, parC, parE. At the same time,4isolates, with MIC≤0.25mg/L against ciprofloxacin, were used for comparison. Homology analysis of17isolates from different areas of Beijing was performed by using the method of pulsed field gel electrophoresis.Results:The identification results of API20Strep Identification System and MALDI-TOF MS indicated that all of the48strains were S. pyogenes. Sensitive rates of S. pyogenes to levofloxacin, ampicillin and penicillin were all100%. The resistance rates to tetracycline, erythromycin and clindamycin were91.7%,91.7%and89.6%, respectively. MIC50of ciprofloxacin, levofloxacin and moxifloxacin was2mg/L,1mg/L and≤0.25mg/L, MIC90was4mg/L,2mg/L and0.5mg/L, respectively. Of the48isolates of S. pyogenes,12isolates showed the MIC at4mg/L, while one isolate has a MIC against ciprofloxacin at8mg/L, which isolated from Chaoyang district. Analysis of sequence of chromosome mediated quinolones resistance genes in those13ciprofloxacin non-susceptible isolates exhibited that there were12isolates that harbored Ser79Phe/Tyr mutation and10isolates which harbored Ala121Val in parC gene. It is shown that an 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 raise to ciprofloxacin MIC (MIC=4mg/L). There were no mutations in gyrA and gyrB genes. The PFGE results demonstrated that the17tested isolates could be divided into7clones. The clone A isolates from Chaoyang, Daxing.Fengtai, Shunyi and Shijingshan district have a MIC≥4mg/L against ciprofloxacin, which covered69.2%of all MIC≥4mg/L isolates. The clone C isolates from Huairou district were MIC≥4mg/L isolates. B,D,E,F and G clones isolates come from different districts.Conclusion:The mutation of parC gene was the main reason that contribute to the slightly increase of ciprofloxacin MIC in S. pyogenes isolated from Beijing districts. The PFGE analysis showed that there was a small scale prevalence caused by the infection of S. pyogenes in some districts.