ObjectiveTo analyze the clinical distribution and antimicrobial resistance profile of Serratia marcescens(S. marcescens), and to provide the scientific evidence supporting clinical diagnosis and treatment.MethodsThe antimicrobial susceptibility test was performed in 104 strains of S. marcescens by agar dilution method. The results were judged according to the criteria recommended by Clinical and Laboratory Standards Institute (CLSI) 2010.The data were analyzed by chi square test. Results The majority of S. marcescens were isolated from sputum specimens,accounting for 59.6％ (62/104). The bacteria were most frequently isolated from department of respiratory (33.7％,35/104),followed by intensive care unit (23.1％,24/104),department of gerontology (16.3％, 17/104). The results of antimicrobial susceptibility test showed that the resistance rates of S.marcescens against ampicillin,gentamicin and cephazolin were high,which were 90.4％,86.5％ and 79.8％,respectively; those against the 3rd generation of cephalosporins were 24.0％-43.3％. No imipenem and meropenem resistant strains were identified. Compared with cefoxitin-resistant strains,the resistance rates of non-cefoxitin resistant strains against piperacillin (82.9％ vs 28.6％),ceftazidime (63.4％ vs 9.5％),aztreonam (68.3％ vs 9.5％),amikacin (68.3％ vs 20.6％),ciprofloxacin (48.8％ vs 19.1％) and chloramphenicol (90.3％ vs 58.7％) were all lower (all P ＜ 0.05 ). Conclusions S. marcescens is one of the most common conditional pathogenic bacteria leading to nosocomial infections,which is resistant to many kinds of antimicrobial agents.The surveillance of antimicrobial resistance in S. marcescens should be strengthened for purpose of preventing the transmission of multidrug resistant strains.

ObjectiveTo investigate the variations and distributions of the plasmid-mediated quinolone resistance genes in clinical isolates of Shigella and their resistance to antimicrobial agents. Methodsqnr, aac(6')-Ib-cr and qepA genes were identified by polymerase chain reaction (PCR) in 137 clinical isolates of Shigella.DNA sequencing of gene-positive strains were analyzed and the conjugation experiment was performed. The minimal inhibitory concentrations (MIC) of Shigella isolates, recipient strains and transconjugants were tested by agar dilution method for quinolones and other antimicrobial agents. The genotype of transconjugants were determined by PCR and sequencing. ResultsFour (2.9％) strains of the 137 Shigella isolates were qnr gene positive, including 3 qnrS2 positive and 1 qnrB4 positive (GenBank accession numbers of the complete sequence were JF261185 and HQ917003, respectively).Furthermore,five (3.6％) aac ( 6')-Ib-cr gene-positive strains (GenBank accession number JF261186 ) and one (0.7％) qepA gene-positive strain were identified in all isolates. The conjugation experiments were successfully carried out in six out of ten PCR-positive isolates. The MIC of transconjugants against quinolones and other antimicrobial agents increased differently compared to recipient strains. Conclusions The plasmid-mediated quinolone resistance genes are lowly prevalent in clinical isolates of Shigella. However, these resistance genes have the characteristic of horizontal transfer, which indicates that more attention should be paid to this phenomenon.