Susceptibility determination of Chlamydia trachomatis to several antibiotics from 2012 to 2014 in Guangzhou

Objective To detect and compare activities of eight antibiotics against recent clinical isolated genital chlamydia trachomatis(C.t)in vitro,and to analyze the change of drug susceptibility.Methods Strains of clinical isolated C.t was cultured and passaged in McCoy cell culture,70 strains reached 90% monolayer cell infection.With double dilution method,MIC assay of these 70 strains was performed in 96 well Plates.The Minimum inhibitory concentration(MIC)of each agent was defined as the lowest concentration of drug at which no typical inclusions were identified after the first passage in McCoy cell culture.In order to compare and analyze the change of drug susceptibility,70 strains were divided into three group(23strains of 2012 group,24strains of 2012 group and 23 strains of 2014group).Results Quinolones MIC value in group 2012 was significantly higher than that in the other two groups,which has reached levels of resistance.The antibacterial activity of group 2013 and group 2014 recovered to the level of sensitivity.The MIC90 respectively was,2012group:levofloxacin MIC90=8.0mg/L;sparlfoxacin MIC90= 5.12mg/L;moxifloxacin MIC90= 2.0mg/L.2013group:levofloxacin MIC90= 0.5mg/L;sparlfoxacin MIC90 0.04mg/L;moxifloxacin MIC90=0.0032mg/L.2014group:levofloxacin MIC90= 0.5mg/L;sparlfoxacin MIC90 0.04mg/L;moxifloxacin MIC90 0.0016mg/L.The MIC90 of Azithromycin in group 2013 and group 2014 were 4times higher than group 2012,but still belongs to the sensitive level.The MIC90 respectively was,2012:0.0064mg/L;2013:0.025mg/L;2014:0.025mg/L.Other drugs was approximately the same MIC value between groups.Conclusions Quinolones MIC value decreased significantly in group 2013 and 2014,suggesting that the susceptibility increased.This may be due to the publicity and promotion of the rational use of antimicrobial drugs.Tetracycline and macrolide drug susceptibility have no obvious change.This suggested the antibacterial activity of these drugs were excellent,and broadly in line with the clinical experience.