| Objective:To screen vaginal-rectal swabs of pregnant women at 35-37 weeks and analyze the epidemiological characteristics of drug resistance,drug-resistant phenotypes,drug-resistant genes,virulence genes,serological typing,and molecular typing of Streptococcus agalactiae(GBS)in women in late pregnancy to provide molecular epidemiology for effective prevention and treatment of maternal and neonatal GBS infection data.Methods:Vaginal-rectal swabs from 35-37 weeks pregnant women attending our outpatient clinic from January 2016 to February 2022 were screened,isolated and cultured,and GBS strains were identified by CAMP assay and mass spectrometry using MALDI-TOF MS.44 GBS strains were collected,and the minimum inhibitory concentrations of GBS strains to common antimicrobial drugs were detected using Etest test strips,and D-tests were performed to determine the drug-resistant phenotype.The D test was performed to determine the resistance phenotype.The serotype analysis was performed using the blast serotype database,and the strains were identified by MLST analysis using mlst(https://github.com/tseemann/mlst)software.PhyML v3.0(http://www.atgc-montpellier.fr/phyml/)was used to construct ML(Maximum Likelihood)phylogenetic trees.The protein sequences of the predicted genes were compared with the CARD and VFDB databases,respectively,to obtain the drug resistance genes and virulence genes carried by the GBS strains.The sample results were statistically analyzed by SPSS26.0.Results:(1)A total of 44 GBS strains were tested,and the results of drug sensitivity tests:44 GBS strains were sensitive to penicillin,cefotaxime,vancomycin,and linezolid,and the insensitivity rates to erythromycin,clindamycin,levofloxacin,tetracycline,and chloramphenicol were 90.9%(40/44),93.2%(41/44),68.2%(30/44),47.7%(21/44),and 4.5%(2/44).(2)Results of drug-resistant phenotypes:0 iMLSB phenotypes,39 cMLSB phenotypes,1 M phenotype and 2 L phenotypes were obtained by the D experiment.(3)Serotyping results:Serotypes Ⅰa,Ⅰb,Ⅱ,Ⅲ and Ⅴ were the five main types,of which Ⅰa accounted for 13.6%(6/44),Ⅰb 47.7%(21/44),Ⅱ 2.3%(1/44),Ⅲ 27.3%(12/44)and Ⅴ9.1%(4/44).(4)MLST typing results:a total of 9 Sequence Types(STs)and 4 NT types were classified.Among them,ST10 type was the most abundant accounting for 40.9%(18/44),followed by ST19 type accounting for 22.7%(10/44),and the remaining 7 ST types accounted for 4.5%(2/44),ST4 type accounted for 2.3%(1/44),ST8 type accounted for 2.3%(1/44),ST12 type accounted for 2.3%(1/44),ST17 type accounted for 4.5%(2/44),and ST23 type accounted for 4.5%(1/44).(The five clonal complexes CC12,CC19,CC23,CC1 and CC17 accounted for 47.7%,22.7%,9.1%,4.5%and 4.5%of the four NT types,respectively.Among the four NT types,strains 190412064 and 211203035 had a high affinity with CC12,strain 200515006 had a high affinity with CC23,and strain 210906017 had a high affinity with CC1.(5)Results of drug resistance genes:the highest number of drug resistance genes were detected in mreA(44/44)100%,followed by ermB 72.7%(32/44),tetM 45.5%(20/44),mefA 20.5%(9/44),msrD 20.5%(9/44),lnuB 20.5%(9/44),respectively lsaE18.2%(8/44),lsaC9.1%(4/44),tetO9.1%(4/44),tetL9.1%(4/44),cat9.1%(4/44),aac(6’)-aph(2")9.1%(4/44),ermA6.8%(3/44)and lnuC2.3%(1/44).No tetK,par and gyr resistance genes were detected.(6)The results of virulence gene comparison:pavA,neuA,sip,cylE,cfb,lmb,fbsB,scpA/scpB,fbsA,and hylB carriage rates were 100%,100%,100%,100%,100%,97.7%,90.9%,77.3%,and 77.3%.Conclusions:(1)The 44 strains in this study were mainly resistant to erythromycin,clindamycin,levofloxacin and chloramphenicol,and the resistance rate was significantly higher than the national average,and penicillin is still the first choice for GBS infection prophylaxis in this region.(2)Serotypes with Ib type accounted for the largest proportion.The serotypes prevalent in most of the regions in China are type Ⅲ,and there is some variability,showing that the serotypes have certain geographical characteristics.(3)Erythromycin resistance genes were mainly ermB genes;tetracycline resistance genes were mainly tetM.pavA,neuA,sip,cylE,cfb,lmb virulence genes were all carried,and the carrying rates of fbsB,scpA/scpB,fbsA,hylB were 97.7%,90.9%,77.3%,77.3%.This is consistent with the domestic prevalence.(4)The MLST typing was divided into 9 ST types and 4 NT types,among which the ST 10 type was the most.5 clonal complexes,the most accounted for by CC12.evolutionary analysis showed that more than 50%of the strains in this study belonged to or hada high affinity with CC12.(5)The incidence of adverse pregnancy was 55.3%,and those with adverse pregnancy outcomes were mainly ST10/Ib type and ST19/Ⅲ type,and the incidence of maternal adverse pregnancy in this study was not correlated with age.(6)Some of the serotypes were analyzed to be correlated with MLST typing,and different MLST typing,serotypes and some resistance phenotypes,resistance genes and virulence genes existed,and the resistance rates of erythromycin and clindamycin were high and the resistance mechanisms were complicated. |
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