Drug resistance status of Streptococcus agalactiae in pregnant women in the third trimester of pregnancy and its serotype and virulence gene analysis
Objective To analyze the distribution of capsular serotypes and virulence genes of genital Streptococcus agalactiae in pregnant women in the third trimester of pregnancy and the correlation between the resistance rates to erythromycin and clindamycin,with positive D test rates to provide a basis for the prevention,control,and treatment of group B Streptococcus(GBS)infection.Methods The GBS strains clinically isolated from pregnant women in the third trimester of pregnancy from the First Affiliated Hospital of Kunming Medical University from November 2021 to October 2022 were collected,and the drug susceptibility experiment was carried out by the standard paper diffusion method;capsular serotyping was carried out by multiplex PCR;virulence gene analysis was performed by the PCR method;WHONET 5.6 was used for drug susceptibility analysis;and SPSS26.0 was used for statistical analysis.Results A total of 168 strains of Streptococcus agalactiae were collected,and the highest detection rate of serotype Ⅲ was 31.5％(53/168),followed by 31.0％(52/168)of type V,25.0％(42/168)of typeⅠb,and 7.7％(13/168)of type Ⅰa.The detection rate of type Ⅱ and Ⅳ was rare,and type Ⅳ,type Ⅶ,type Ⅷ,and type Ⅸ were not detected.Among the 9 different virulence genes,each strain contained at least 3 virulence genes,among which the detection rates of the cylB,fbsA,and fbsB gene were 100.0％(168/168),the detection rates of the hylB,lmb,and scpB gene were all greater than 91.0％,and the detection rate of the bac gene was the lowest(27.0％)(47/168).The expression rates of bca and bac genes in serotype Ⅰb were significantly higher than those of other serotypes(P＜0.05),which were 92.1％(39/42)and 88.1％(42/47),respectively,and the expression rates of bac genes in serotype Ⅲ were significantly lower than those of other serotypes(P＜0.05),which were 3.8％(2/53).No strains resistant to penicillin and vancomycin were detected,and the resistance rates to clindamycin and erythromycin were 76.7％and 70.8％,respectively.The resistance rates of clindamycin and erythromycin were significantly different among different serotypes(P＜0.05).The positive rate of the D test was 16.6％(28/168),and the positive rate of the D test was 85.7％(24/28)among V serotypes,which was significantly different from other serotypes(P＜0.05).Conclusion The serotypes of GBS in the genital tract of pregnant women in the third trimester of pregnancy were mainly type Ⅲ and Ⅴ,and there were more than three virulence genes.There were also differences in the expression rate of virulence genes,the positive rate of the D test,and the resistance rates of erythromycin and clindamycin among different serotypes.No strains resistant to penicillin G or vancomycin have been found,and penicillin could still be used as the drug of choice for the treatment of Streptococcus agalactiae infection.
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