Study On The Molecular Characteristics Of Levofloxacin Resistant Streptococcus Agalactiae Isolated From Suzhou Region

Objective Streptococcus agalactiae,also known as group B streptococcus(GBS),is a conditional pathogen,which can cause disease in all age groups,especially severe infections such as neonatal meningitis and septicemia.In order to find out the molecular characteristics of levofloxacin-resistant S.agalactiae in Suzhou,this study analyzed the distribution of drug-resistant,drug-resistant genes,serotypes,MLST and the characteristics of protein mass spectrometry of clinical isolates of S.agalactiae from 2018 to 2019,and explored the relationship between them.Try to explore the value of protein mass spectrum characteristic peak in clinical rapid diagnosis of levofloxacin-resistant strains,and lay a foundation for better guidance of clinical accurate anti-infection treatment in the future.Methods A total of 132 isolates of S.agalactiae were collected from January 2018 to January 2019,the drug resistance and phenotype were evaluated by drug sensitivity test.PCR and Sanger gene sequencing methods were used to detect the gene mutations of gyr A,par C and par E,as well as the serotype-associated genes and multi-locus sequence typing.The protein peaks of levofloxacin-resistant strains were detected and collected by mass spectrometry.Clin Pro Tools 3.0 software was used to screen and verify the levofloxacin-resistant specific peaks of mass spectrometry of proteomics in the S.agalactiae isolates.Result1.Epidemiological characteristics of S.agalactiae in Suzhou: the main source of clinical isolated S.agalactiae is the genital tract culture specimens;S.agalactiae was the main pathogen in the positive specimens of reproductive tract culture from 2014 to 2018,accounting for 31.8% ～ 41.5% of the positive samples;its drug resistance was mainly reflected in the resistance to erythromycin,clindamycin and levofloxacin,with 62.9%,66.7% and 43.9% respectively;it was highly sensitive to penicillin,and no resistance was detected;serotype III was the most common serotype,accounting for 57.6%.2.Erythromycin and clindamycin resistance analysis results: the main drug-resistance phenotype was c MLS phenotype,accounting for 55.3%;erm B positive strains were the most common;mef A /E positive strains had lower resistance rates to erythromycin and clindamycin than erm B positive strains;59.4% of c MLS phenotype strains were single erm B positive strains,and all M phenotype strains carried mef A / E resistance genes.3.Analysis of levofloxacin-resistance results: the main mechanism of levofloxacin-resistance S.agalactiae in this region was due to the mutation of gyr A gene and par C gene,mainly carrying gyr A＿Ser81Leu + par C＿Ser79Tyr +par E＿His225Tyr mutation,accounted for 44.8%,and most of them were serotype III and ST19.4.Rapid identification and evaluation of mass spectrometry: mass spectrometry profile analysis for S.agalactiae showed that 6894,3445,5076,4544 and 3721 m/z were the dominant specific differential peaks of the levofloxacin-resistant S.agalactiae isolates.And the sensitivity rate of predicting by genetic algorithm whether S.agalactiae was levofloxacin-resistance was 90.9%,and the specificity was87.5%.Conclusion S.agalactiae isolated from Suzhou region is the main pathogen of genital tract culture of pregnant women.There are mainly five serotypes Ia,Ia,III,V and VI,among which serotype III is the most common.The resistance rates of erythromycin and clindamycin were high.Most of the resistant phenotypes were c MLS phenotype and mainly expressed erm B gene,the drug-resistance model is more consistent with domestic and foreign reports.The drug-resistance of levofloxacin is consistent with the domestic reports,but much higher than that of foreign reports,it’s suggested that there are great epidemiological differences between China and other regions.Further study of its molecular characteristics shows levofloxacin-resistant strains mainly carry gyr A＿Ser81Leu + par C＿Ser79Tyr + par E＿His225Tyr mutation,most of them were serotype III and ST19.In addition,6894 M / Z and other characteristic peaks were obtained,which can be used for rapid identification of clinical levofloxacin-resistant strains and provide the basis for guiding clinical rational drug use in the future.