Population Variation And Genetic Characteristics Of Virulence Genes Of Neisseria Meningitidis In China

Neisseria meningitidis(Nm)usually inhabits in approximately 10?20%of the population,often asymptomatically,but also an important and devastating human pathogen which causes invasive diseases mainly including the epidemic cerebrospinal meningitis and septicemia.Epidemic cerebrospinal meningitis is one of the notifiable infectious diseases in China,which is covered by class I vaccine,and the fatality rate is as high as 10%?15%.Capsule polysaccharide(CPS)is an important virulence factor and the main ingredient in vaccines.According to the structure of CPS,Nm could be clustered into 12 serogroups.Population variation includes phenotypic variation and genetic variation,Multilocus sequence typing(MLST)is one of the common molecular typing methods,and it could be used to identify clonal relationships among Nm strains.The endemic serogroups in different countries(regions)have obvious regional characteristics,there is a corresponding relationship between the main serogroups and the clonal complexes(CCs).The same serogroup/CC has different characteristics of CC/serogroup.Previous studies have shown that Chinese Nm strains have unique epidemic characteristics and switch patterns.In recent years,the emergence and prevalence of novel Nm have become a potential challenge for the prevention and control of Nm,and it is urgent to have a comprehensive understanding of the overall prevalence and variation of Chinese strains,so as to prepare for new epidemic situations and formulate corresponding prevention and control strategies.It is known that the genes involved in Nm capsule synthesis and transport are located in the cps.Previous studies have analyzed the gene composition of cps in foreign Nm strains,while the genetic composition and characteristics of cps in Chinese strains are still unknown.In addition to CPS,autotransporter proteins are also one of the virulence factors of Nm.To date,8 types of autotransporters have been studied in Nm.The functions of the autotransporters in virulence,adhesion and colonization and their various interactions have been studied abroad,but these are still blank in China.This study conducted a comprehensive analysis of the MLST of 1641 Chinese Nm strains over the past 60 years.It found that serogroup A was conservative,the main prevailing CCs were CC1 and CC5.The sequence types(STs)in serogroup B and C were diversely and the mainly CC was CC4821 while serogroup W were mainly CC11 and CC4821.When coming to CC4821,most of the serogroup C strains belonged to ST-4821 while the majority of serogroup B strains belonged to other STs,all the ST-8491 were serogroup W strains.Serogroup Y strains were mainly CC 175.Most of the serogroup E strains clustered into a subCC5586 of UA.Due to the few strains of other serogroup,no obvious cluster was observed.We detected one genogroup A strain from nongroupable(NG)strains.According to the previous researches,capsule null locus(cnl)strains were all CC198,it suggested that not all the cnl strains belonged to CC198 as we found 2 CC4821 and 2 UA strains in cnl.There have two strains could not be typed by serotyping or genotyping and was named as nongenogroupable(NGG).This study analyzed the genetic characteristics of cps of various serogroups in China.In addition to the existing“D-A-C-E-D'-B”,another arrangement of the six regions in cps is“B-D-A-C-E-D'”.Analysis of cps in the NG strain of genogroup A revealed that its formation mechanism might be codon change caused by base deletion of csaB gene,which affected capsule expression.Intact cssF gene was found in serogroup W.A new type of NG cps formation mode was found,in which the tex gene was also lost as well as region A and region C.In this study,the characterization and distribution of the 8 autotransporter genes in Chinese strains were demonstrated.All the 188 Nm strains carried app,iga,nhha and autA genes while 112 carried autB,179 carried nalP,158 carried ausl and only 20 carried nadA.Absent of autB gene in CC4821 strains indicated that not all highly pathogenic strains were autB-positive.The nalP gene may be obtained by homologous recombination,and the null strains may be caused by the presence of removable repeat elements in the spacer region.No premature termination was found in the AusI phase on strains.The nadA gene was not found in the most prevalent CC4821,NadA may not applicable for serogroup B vaccines in China.When the app gene is transcribed into amino acid sequence,no premature termination occurs,and its function may be necessary for Nm.The iga gene has very high sequence diversity,the amino acid sequence of the 6 CC11 strains were different to foreign strains.The nhhA gene sequences in CC1,CC5 and CC198 were relatively conserved,while the UA strains were highly variable.The expression of autA gene is under obvious selection pressure.Above all,the MLST of Chinese Nm strains were studied in this research,many novel types of Nm strains were found,and it provided important reference data for understanding the population variation of Chinese strains.The genetic characteristics of cps provides the genetic basis for studying the changes of serogroups of Nm.The characteristics and distribution of the 8 autotransporters laid the foundation for subsequent study of the functions and mechanisms.