| Objective To understand the prevalence of group B Streptococcus(GBS)among healthy pregnant women,and investigate the influencing factors,antibiotic susceptibility and molecular characteristics of the isolates,and also explore the differences of virulence and resistance characteristics among different molecular typing isolates,which may be helpful to prevent and control the GBS related diseases.Method A cross-sectional study was conducted in Shenzhen city,where healthy pregnant women were recruited to finish the questionnaire and provide the vaginal swab.The identification of GBS was confirmed by the traditional biochemical tests.Antibiotic susceptibility testing of was performed by the disk diffusion method.Polymerase chain reaction was used to identify the serotypes,virulence and resistance genes.Multilocus sequence typing was performed to identify the sequence type of the isolates.EBURST analysis was used to ascertain the clonal complex of the isolates.Chi-square test or Fisher’s exact test was used to compare rates.Univariable and multivariable non-conditional logistic regression models were used to analyse the influencing factors.Correspondence analysis was used to explore the relation between the serotype and sequnence type.Fisher’s exact test was used to assess the difference of characteristics among different molecular typing isolates.Results 1.Prevalence of carriage: The overall prevalence of GBS carriage among the study population was 4.9%(104/2121).2.Iinfluencing factors: Body mass index(BMI)before pregnancy,gynecological lotion usage in the year before pregnancy and artificial abortion would influence the carriage of GBS among pregnant women.Obesity(BMI before pregnancy≥28.0)could increase the carriage of GBS compare to normal weight(BMI before pregnancy=18.5-23.9)(OR=4.40,95%CI: 1.46-13.24);pregnant woman who used gynecological lotion in the year before pregnancy had more risk on carring GBS than those didn’t(OR=1.58,95%CI: 1.03-2.43)artificial abortion before would decrease the carriage of GBS(OR=0.64,95%CI: 0.41-0.99).3.Antibiotic susceptibility: GBS isolates were resistance to tetracycline(76.9%),erythromycin(72.1%),clindamycin(66.4%)and levofloxacin(27.8%).All isolates were susceptible to penicillin,vancomycin,ceftriaxone and linezolid.71.2% isolates were multidrug-resistant,and 21.2% isolates were simultaneously nonsusceptible to erythromycin,clindamycin and levofloxacin.Tet M and tet O were the primary tetracycline-resistant genes found among isolates resistance to tetracycline and there were 22.5% isolates carried two tetracycline-resistant genes simultaneously.Erm B and mef A/E were the primary erythromycin-resistant genes found among isolates resistance to erythromycin,and there were 24.0% isolates carried two erythromycin-resistant genes simultaneously.4.Molecular characterization: A total of six serotypes were identified in this study,the predominant serotype was III(49.0%),Ia(22.1%)and V(18.3%).A total of 15 STs were identified in this study,the predominant STs were ST19(20.2%),ST12(14.4%),ST17(14.4%),ST10(10.6%)and ST651(10.6).CC19 was the most predominant clonal complex(CC),followed by CC17,CC12 and CC103.All isolates carried scp B and hyl B virulence genes,and 99 isolates carried surface alp genes,including Rib(38.5%)、Alpha C(26.9%)and Epsilon(26.9%).5.Relations between serotypes and STs: ST17/III(12.5%)and ST19/III(18.3%)were the predominant isolates in this study and we found there were relations between serotypes and STs which could be proved by correspondence analysis(c2=181.92,P<0.001).Serotype III had a relation with ST17,ST19,ST27,ST86,ST651 and ST862.Seroytpe V had a relation with ST1,ST10 and ST12.Serotype Ia had a relation with ST23,ST24,ST103,ST485,ST624 and ST652.6.Analysis of characteristics between different serotypes: There was statistically significant differences among different serotype isolates with regard to virulence and antibiotic susceptibility characteristics.Serotype III isolates were more likely to carried Rib virulence gene,and erm B,tet M,tet O resistant genes and resistance to clindamycin and levofloxacin.Serotype V isolates were more likely to carried Alpha C virulence gene,and erm B,tet M,tet O resistant genes and resistance to clindamycin and levofloxacin.Serotype Ia isolates were more likely to carried Epsilon virulence gene,and mef A/E,tet M resistant genes.7.Analysis of characteristics between different STs: There was statistically significant differences among different ST isolates with regard to virulence and antibiotic susceptibility characteristics.Almost all ST17 and ST19 isolates carried Rib,all ST10 and ST12 isolates carried Alpha C,all ST651 isolates carried Epsilon.And ST19 isolates were more likely to resistance to tetracycline,erythromycin,clindamycin,levofloxacin and carried erm B,mef A/E,tet M resistant genes.ST12 and ST17 isolates were more likely to resistance to tetracycline,erythromycin,clindamycin and carried erm B,tet O resistant genes.ST10 isolates were more likely to resistance to erythromycin,clindamycin,levofloxacin carried erm B resistant genes.ST651 isolates were more likely to carried tet M resistant genes.Conclusion The low prevalence of GBS carriage(4.9%)was found among healthy pregnant women in Shenzhen city.BMI before pregnancy,gynecological lotion usage in the year before pregnancy and artificial abortion would influence the carriage of GBS among pregnant women.Serious antibiotic resistance were found in this study,with most isolates were resistance to tetracycline,erythromycin,clindamycin and levofloxacin.There were 21.2% isolates simultaneously nonsusceptible to erythromycin,clindamycin and levofloxacin.Tetracycline-resistant genes(tet M and tet O)and erythromycin-resistant genes(erm B and mef A/E)were found in most isolates.The predominant serotype was III,Ia and V.The predominant STs were ST19,ST12,ST17,ST10 and ST651.The predominant CCs were CC19,CC17,CC12 and CC103.ST19/III and ST17/III were the predominant isolates in this study and there were relations between serotypes and STs.Significant differences of virulence and antibiotic susceptibility characteristics were found among different molecular typing isolates,which may be helpful to understand the pathogenicity and harmfulness of the isolates. |
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