Antimicrobial Resistance And Mechanism Research Of Streptococcus Agalactiae

Streptococcus agalactiae,also known as Group B Streptococcus(GBS),is a conditional pathogen that is parasitic in the lower digestive tract and genitourinary tract of humans.Once the host immunity is reduced or microecology is out of balance in the genitourinary tract,and colonization site is changed,infections of S.agalactiae can be caused.Streptococcus agalactiae infection causes great harm to human health,especially the health of maternal and newborn.The guidelines issued by the Centers for Disease Control and Prevention(CDC)recommend prenatal screening for S.agalactiae colonization in vaginal and rectal in all pregnant women between 35 and 37 weeks of gestation,making intrapartum antibiotic prophylaxis in women with identified S.agalactiae or risk factors.The purpose of this project is to research the antimicrobial resistance and it's mechanism of Streptococcus agalactiae,in order to provide basis for clinical prevention and treatment of Streptococcus agalactiae infection.This research includs the following two parts:I.Research on antimicrobial resistance of Streptococcus agalactiaeFor the retrospective analysis,this research collected the antimicrobial susceptibility test results and information of 620 strains(the same strain isolated from the same patient has been removed)of Streptococcus agalactiae isolated from Zhujiang Hospital of Southern Medical University from 2008 to 2018.After isolating from clinical samples such as vaginal secretions,blood,urine or cerebrospinal fluid,identification and antimicrobial susceptibility test were performed.The data were collected by WHONET and grouped according to the year,the age of the patient,the source of the sample,and the strain as colonization or infection.The antimicrobial resistance rate of Streptococcus agalactiae and the difference of resistance rate among different groups were analyzed.Statistical analysis was performed with SPSS 20.0,the count data was described by rate,the chi-square test was used to compare the data of different groups.The difference was statistically significant at P<0.05.No strains resistant to penicillin G,ampicillin,vancomycin,linaprilamine or quinupidine/dafoprein in 620 isolates,and the resistance rates to tetracycline,erythromycin,clindamycin and levofloxacin were 86.8%,57.4%,38.6%,25.3%respectively.Penicillin can still be used as preferred antibiotic for the prevention and treatment of Streptococcus agalactiae in our hospital.As second-line antibiotic for the prevention and treatment of Streptococcus agalactiae,the clinical value of erythromycin and clindamycin should be re-evaluated.In 2008-2018,there was no significant difference in the resistance rates of Streptococcus agalactiae to erythromycin,clindamycin,tetracycline and levofloxacin between different years(P>0.05).The resistance rate of Streptococcus agalactiae to erythromycin,clindamycin,tetracycline and levofloxacin was not statistically different between different age of patients,whether strains were colonized or infected(P>0.05).There was no significant difference in the resistance rate of Streptococcus agalactiae to erythromycin,clindamycin and tetracycline between different kinds of samples(P>0.05),while strains isolated from genital tract secretions and urine had higher resistance rate to levofloxacin than that from blood and cerebrospinal fluid,and the difference was statistically significant(P<0.05).In the clinical prevention and treatment of Streptococcus agalactiae infection,the drug sensitivity test should be performed,and the treatment should be personalized.II.Research on antimicrobial resistance mechanism of Streptococcus agalactiaeGenome sequencing of 29 Streptococcus agalactiae isolated from Zhujiang Hospital of Southern Medical University from September 2012 to September 2017 was performed.Among them,15 strains were from secretions,9 strains were from blood,4 strains were from cerebrospinal fluid,and 1 strain was from fetal membranes.The antimicrobial resistance phenotype and resistance genes of 29 strains were analyzed by antimicrobial susceptibility test and bioinformatics analysis to study the resistance mechanism of this group of Streptococcus agalactiae.The results showed thatthe resistance phenotypes of 29 strains to erythromycin and clindamycin were mainly cMLSB type,followed by M type and iMLSB type,and L type was also found.Of the 29 strains,26 were resistant to tetracycline and 5 were resistant to levofloxacin.The resistance mechanism to erythromycin in this group was mainly methylation of 23SrRNA binding site mediated by erm(B)gene and macrolide efflux pump mediated by mef(A)gene.In this study,8 strains had mef(A)gene with msr(D)gene in the downstream about 110-120bp,7 strains had lincolamide resistance gene lnu(B)with Isa(E)gene in the upstream of 53 bp.At present,research in this area is rare.The resistance of Streptococcus agalactiae to erythromycin and clindamycin is regulated by multiple genes,and its mechanism and genetic characteristics need to be further explored.The Streptococcus agalactiae resistant to tetracycline in this group was mainly caused by the ribosome protective protein encoded by tet(M)and tet(O)genes,and tet(L)gene encoding the external pump protein and tet(S)gene encoding the ribosome protective protein were also detected.In addition,a tetracycline-resistant strain containing the mosaic gene tet(0/VW/32/O)was detected and it had not been reported in Streptococcus agalactiae.The molecular characteristics of these genes will be further analyzed in the future.The fluoroquinolone resistance genes were not detected in the 5 strains resistant to levofloxacin.Maybe the resistance to quinolones is caused by amino acid mutations in the quinolone resistance determining regions(QRDRs)GyrA subunit(encoded by gyrA)and/or ParC subunit(encoded by parC),or there are other resistance mechanisms,that need to be confirmed next.