Population Structure,Drug Resistance And Virulence Of Staphylococcus Haemolyticus From A Hospital In Guangdong Province

BackgroundStaphylococcus haemolyticus,an opportunistic pathogen,is the second most common Co NS in clinical infection,which lead to pneumonia,sepsis,peritonitis and other infectious diseases.And the multi-drug resistance of S.haemolyticus has greatly hindered clinical anti-infection treatment.Further,most strains can form biofilms,and studies have shown that S.haemolyticus is the most virulence strain in Co NS.Recently,small outbreaks of S.haemolyticus have occurred in Chinese hospital,which has aroused clinical attention.However,studies on population structure,drug resistance and virulence of hospital-derived S.haemolyticus based on WGS are lacking.ObjectiveThis study aims to clarify the epidemiological characteristics of various sources S.haemolyticus from a hospital in Guangdong Province.Then,we elaborate the characteristics of antibiotic resistance and virulence of the strains,and provide monitoring guidance and coping strategies for S.haemolyticus related infectious diseases.Methods1.Clinical samples of patients and ward environment were collected from a hospital in Guangdong province.Then,S.haemolyticus strains were cultured,isolated,identified and preserved.The nosocomial epidemic distribution of strains was described based on clinical records.2.The population characteristics of S.haemolyticus.1)97 S.haemolyticus strains were selected for WGS,and 336 genome of S.haemolyticus strains were downloaded from NCBI database.2)The MLST,CC cluster analysis and phylogenetic analysis were performed based on WGS.3.The genotypes and phenotypes of drug resistance in S.haemolyticus.1)The ABRicate V0.8.7,ISFinder and SCCmec Finder 1.2 database were used to identify and analyze the distribution of ARGs and mobile elements in 97 S.haemolyticus strains based on WGS.2)The NCBI genome data were used to analyze the global distribution of ARGs,to clarify the genomic characteristics and molecular distribution of S.haemolyticus.3)The drug sensitivity of 97 strains to antibiotics was determined to evaluate the drug resistance phenotype.4.The virulence characteristics of S.haemolyticus.1)The virulence genes of 97 S.haemolyticus strains were identified using WGS data,and then the prevalence and distribution of virulence genes in different populations were analyzed.2)The NCBI genomic data are used to analyze the global distribution of virulence genes of S.haemolyticus.3)Biofilm formation ability of strains was evaluated by biofilm quantitative assay.4)The virulence or pathogenicity of S.haemolyticus was evaluated by the virulence infection test of Galleria mellonella.Results1.A total of 311 S.haemolyticus strains were isolated from 1213 samples,including176 from ward environment,83 from faecal swabs,43 from nasal swabs,7 from bronchoalveolar lavage fluid,and 2 from throat swabs.In addition,the strains were mainly concentrated in patients with respiratory diseases.2.The population characteristics of S.haemolyticus.1)In this study,a total of 9 known ST types and 27 new ST types were identified from97 sequenced strains,among which the dominant clonal lineage was ST42.In addition,ST42 was classified as CC29.2)Phylogenetic tree showed that 97 strains in this study had a diversity of genome structure,forming multiple linkage groups.And multi-source ST42 strains formed specific evolutionary branches.3.The drug resistance characteristics in S.haemolyticus.1)A total of 23 ARGs were identified,and the prevalence of bla Z was 79.4%,mec A and msr（A）was 57.7%,mph（C）was 51.5%,etc.2)The number of ARGs carried by ST42 strains was significantly higher than that of non-ST42 strains.3)Among 56 mec A positive strains,3 strains were identified to have SCCmec elements.4)A total of 38 ARGs were identified from 336 genomes of NCBI,among which the prevalence of bla Z was 71.4%,mec A was 59.8%,mph（C）was 51.2%,etc.5)The 75.3%（77/97）S.haemolyticus strains were MDR strains in this study.The MIC of ST42 was significantly higher than that of non-ST42.4.The virulence characteristics of S.haemolyticus.1)A total of 20 virulence genes were identified from 97 sequenced strains in this study,and the prevalence of atl,ebp and nuc was 100%,lip and cap M was 99%.2)A total of 21 virulence genes were identified from 336 genomic data of NCBI,and the prevalence of atl,ebp,nuc and cap M genes was 99.1%.3)The virulence gene carrying rate of ST42 strains was significantly higher than that of non-ST42 strains.4)Under the condition of tryptone soybean liquid medium,56.7% strains produced film.Among them,29.9% of the biofilms produced by the strains were weakly adherent,19.6% were moderately adherent,and 7.2% were strongly adherent.5)The mortality rate of G.mellonella larvae infected with ST42 was significantly higher than that of non-ST42 in the 24 hours.Conclusion1.In this study,the sources of S.haemolyticus were diverse and widely distributed,suggesting that hospitals were its reservoir.The dominant epidemic ST42 S.haemolyticus was also found,which belonged to the new emergening clonal lineage in China.2.The newly emerging ST42 S.haemolyticus with high burden resistance and high virulence in our hospital may bring new threats to clinical treatment,requiring early clinical monitoring.