Objective To evaluate antimicrobial resistance and antimicrobial resistance mechanisms of Enterococcus faecalis (E.faecalis)to linezolid (LNZ),and provide basis for clinical rational drug use.Methods Twelve E.faecalis strains isolated from sputum of patients who received LNZ therapy in a hospital between January 2012 and January 2013 were collected.The minimum inhibitory concentrations (MICs)of antimicrobial agents were de-termined by agar dilution method,23S rRNA V region gene of E.faecalis was amplified by polymerase chain reac-tion,the amplified products were sequenced.Results Of 1 2 isolates,2 were intermediate strains and 1 0 sensitive strains.The G2576U mutation was detected in 2 intermediate strains,1 of which was also detected G2424U muta-tion;the variations were not detected in 10 sensitive strains.C2424U and G2576U mutation existed in R1 and R4 region respectively.Conclusion 23S rRNA V region gene mutations are found in the intermediate strains of E.faecalis.Change in MIC values of linezolid should be paid close attention in clinical use.

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 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 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.