Abstract: Objective　To investigate the antimicrobial activity of omadacycline (OMC) against clinical Streptococcus agalactiae (GBS) isolates, as well as its relationship with biofilm formation, resistance genes and virulence genes. Methods　A total of 136 strains of Streptococcus agalactiae isolated from Shenzhen Nanshan People's Hospital between 2015 to 2020. The minimum inhibitory concentration (MIC) of OMC against Streptococcus agalactiae was determined by broth microdilution. Crystal violet staining was used to detect the biofilm formation ability of GBS. Resistance genes (tetM, tetO, tetK, ermB, OptrA) and virulence genes (cpsⅢ, bca, fbsA, cpsA, scpB) were investigated by polymerase chain reaction (PCR). Results　Among the 136 clinical isolates of GBS, 20 strains (14.7%) were resistant to OMC, 64 (47.1%) were intermediate, and 52 (38.2%) were sensitive. Fifty-seven strains (41.9%) were biofilm-positive, 20 of which (35.1%) were sensitive to OMC. Seventy-nine strains (58.1%) were biofilm-negative, 32 of which (40.5%) were susceptible to OMC. There was a statistically significant difference in the sensitivity rates between the two groups of strains (χ2=63.062, P<0.001), but there was no significant difference in the sensitivity of OMC among the biofilm-positive strains (Fisher's exact test, P=0.824). The resistance rates of tetM, tetO, ermB and OptrA positive strains were higher than those of negative strains, while tetK was opposite. The presence of tetM (Z=0.815, P=0.415), tetO (Z=0.151, P=0.88), tetK (Z=0.567, P=0.571), ermB (Z=1.198, P=0.231) resistance genes in Streptococcus agalactiae had no significant impact on the sensitivity of OMC. However, the presence of the OptrA resistance gene showed a statistically significant effect on the sensitivity of OMC (Z=2.913, P=0.004). The virulence factors cpsⅢ, bca, fbsA, cpsA and scpB were all detected at a rate higher than 50%. The presence of the virulence genes cpsⅢ (Z=0.222, P=0.824), bca (Z=0.141, P=0.888), fbsA (Z=0.813, P=0.416), and cpsA (Z=1.615, P=0.106) in Streptococcus agalactiae had no significant impact on the sensitivity of OMC. However, there was a significant inter-group difference in the scpB virulence gene (Z=2.844, P=0.004), but the rank mean values and resistance rates of scpB-positive strains were lower than those of the negative strains. Conclusions　The formation of biofilm in Streptococcus agalactiae reduces its sensitivity to OMC, but there was no significant difference in the sensitivity to OMC among the biofilm-positive strains. The presence of resistance genes tetM, tetO, tetK, ermB, and virulence genes cpsⅢ, bca, fbsA, cpsA, scpB in Streptococcus agalactiae is not associated with OMC resistance, but the presence of the resistance gene OptrA is correlated with OMC resistance..

Objective This study was designed to examine the clinical characteristics of bloodstream infections (BSI) caused by Staphylococcus aureus in a teaching hospital and the risk factors for 30-day mortality.Methods A single center retrospective cohort study was conducted for all the patients with BSI caused by S.aureus between 2008 and 2015.The data of clinical features,microbiology,and 30-day mortality were collected from the database of electronic medical records.Results A total of 121 patients with S.aureus BSI were identified.The prevalence of methicillin-resistant S.aureus (MRSA) was 17.4％ (21/121).MRSA BSIs were significantly associated with old age (≥65 years) (P=0.026),hospital acquired infection (P=0.035),respiratory tract infection (P=0.001),polyinfection (P=0.005) and inappropriate initial antibiotic therapy (P=0.001) than methicillin-sensitive S.aureus (MS SA) BSIs.The 30-day mortality was 18.2％ (22/121).Both univariate and multivariate analysis suggested that solid tumor (OR,8.932,P=0.004) and septic shock (OR,56.721,P＜0.001) were independently associated with the 30-day mortality.Conclusions The present study confirms that solid tumor and septic shock are more important risk factors than MRSA in mortality of patients with S.aureus BSI.

Objective To study the homology characteristics of clinicaly isolated and colonized linezolid(LZD)-resistant Enterococcus faecalis (E.faecalis) strains from a patient.Methods Ten E.faecalis strains (2 were isolated from urine specimens and 8 were from stool specimens) isolated from a patient with pulmonary infection were performed antimicrobial susceptibility testing, homology of E.faecalis was determined by pulsed-field gel electrophoresis (PFGE).Results Before and after patients received LZD therapy, 2 E.faecalis strains isolated form urine specimens were both resistant to LZD (MICs: 8 mg/mL, 16 mg/mL, respectively), among 8 strains from stool specimens (6 were isolated before therapy, and 2 were isolated after therapy), LZD susceptible, intermediate, and resistant strains were 4, 2, and 2 respectively(MICs: 0.25-12 mg/mL).10 strains of E.faecalis were homologous by PFGE typing.Conclusion In this case, the detection of E.faecalis from urinary tract and intestinal tract is homologous, which suggested that LZD-resistant Enterococcus may be colonized in vivo for a long time, and may be shift to cause bacterial infection.

Objective To analyze the genomic evolution characteristics of pathogenicity islands (PAIs)in Deng strain of enteropathogenic Escherichia coli (E.coli,EPEC Deng).Methods EPEC Deng was isolated from infant stool specimen,serotypes were identified and antimicrobial susceptibility testing was performed;whole-genome se-quencing was performed by Illumina 2000 system,the locations of prophages(PPs)in the chromosome were detected using PHAST software,collinearity analysis was performed by MUMmer software,phylogenetic trees of homolo-gous gene were constructed in order to understand the evolutional rule of homology gene.PAIs prediction was per-formed using PAI finder software,the homologous evolutionary rule of PAIs core region(LEE)and core genes were clarified,genetic polymorphism was analyzed.Results The serotype of EPEC Deng strain was O119:H6,the strain was resistant to ciprofloxacin,levofloxacin,and ampicillin,but sensitive to other antimicrobial agents.The complete circular chromosome contained 5 025 482 bp with a GC content of 50.52 %,and the plasmid contained 207 564 bp with a GC content of 49.50%.A total of 17 PPs in the chromosomal genome were discovered,phyloge-netic trees analysis suggested that EPEC Deng strain was highly homologous with O26:H11 and O111 :H strains;PAIs and core genes were highly homologous with RDEC-1 and O26:H413/89-1 strains;genetic diversity analysis showed that the intimin (eae)and its receptor tir had high polymorphism,with the pi (π)value>0.10,the genes in type III secretion system was relatively stable.Conclusion The study clarified the genomic evolution characteris-tics of EPEC Deng genome and it’s PAIs,and is helpful for understanding genetic characteristics of native EPEC.

Objective To understand genetic mutation sites in linezolid (LZD)-sensitive and inducible resistant strains of methicillin-resistant Staphylococcus aureus (MRSA) using whole-genome sequencing,and realize mutation sites of LZD-resistant gene.Methods MRSA-MS4 with explicit genotype and whole-genome sequences was induced by LZD of different concentration gradients,LZD-resistant strain MRSA-MS4-LZD100 was obtained,minimum inhibitory concentration(MIC) was detected,domain V of 23S rRNA and ribosomal proteins L3/L4 gene in MRSAMS4-LZD100 were amplified by polymerase chain reaction (PCR),the sequenced products obtained the corresponding mutation site in contrast with the wild-type strain;Illumina PE library was constructed through paired-end sequencing by Illumina HiSeq 2000 technique,and whole genome sequencing was completed based on bioinformatics.Results MRAS-MS4-LZD100 strain was induced after 32 passages,MIC of LZD was 96 μg/mL.Sequencing of PCR products indicated the genetic variations were G2447T mutation in multiple copies of domain V of 23S rRNA gene,and Gly113Val mutation in L3 protein respectively;the whole genome of MRSA-MS4-LZD100 contained 2 744 315 bp,annotation of the whole genome found a total of 2 509 genes,11 tRNA-encoding genes and 2 entire rRNA-encoding operons.The data were submitted to the PubMed,and the GeneBank accession number JXMJ00000000 was assigned;a total of 101 SNPs and 6 Small indels were found,16 of 101SNP mutations occurred in exon,of which the variant proteins with anmino acid sequence alterations included IstB ATP binding domain-containing protein,clumping factor A,IS1272 transposase and so on;3 of 6 Small indel mutations occurred in exon,of which the variant proteins with anmino acid sequence alterations included hypothetical protein,30S ribosomal protein S1,and clumping factor A.Conclusion LZD-resistant strain MRSA-MS4-LZD100 was successfully induced by LZD;beside 23S rRNA V domain and ribosomal L3 protein,the other mutant site exist in this resistant strain,which provide some direction for subsequent study of recessive LZD resistance mechanism.

Objective    To assess the feasibility and safety of percutaneous transcatheter closure of atrial septal defect (ASD) guided by transthoracic echocardiography (TTE) in outpatients. Methods    From December 2016 to June 2018, 50 simple ASD patients underwent TTE-guided transcatheter closure in the outpatient operating room of our hospital (a TTE group) including 22 males and 28 females at the age of 16-48 (27.40±6.95) years. Fifty patients with simple ASD treated with the guidance of conventional fluoroscopy during the same period were treated as a control group, including 22 males and 28 females at the age of 15-48 (28.58±6.96) years. Both groups were re-examined by TTE during follow-up at 1 month, 3 months, 6 months and 1 year. Results    The mean age, body weight, the size of ASD and occluder and success rate had no statistical difference between the two groups (P>0.05). Compared with the control group, the TTE group had significantly lower mean operation time (P<0.01) and less cost (P<0.01) since patients need not to be hospitalized. No related complications were found in the TTE group during follow-up. Conclusion    Percutaneous transcatheter closure of ASD guided by TTE appears safe and effective for outpatients, and can significantly reduce the cost.