Molecular characterization of carbapenem-resistant Klebsiella pneumoniae strains / 中国感染与化疗杂志

Objective To investigate the distribution of common carbapenem resistance genes and virulence genes in and understand the molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) strains.Methods A total of 84 non-duplicate CRKP isolates were collected from Renji Hospital,Shanghai Jiao Tong University School of Medicine and Changzheng Hospital,the Second Military Medical University,in 2015.Kirby-Bauer disk diffusion method was used to test their susceptibility to 15 antimicrobial agents.The HM phenotype of K.pneumoniae was determined by string test.Carbapenem-resistant genes and virulence genes were detected by polymerase chain reaction (PCR).The molecular epidemiology of the 84 isolates were further analyzed by multi locus sequence typing (MLST).The population structure of CRKPs was evaluated by eBURST with the results of MLST.Results Antimicrobial susceptibility test showed that 84 isolates were highly resistant to most antimicrobial agents such as carbapenems,penicillins,cephalosporins and aztreonam.More than 90％ of the strains were resistant to most of the antibiotics tested except ciprofloxacin (77.4％,65/84) and amikacin (82.1％,69/84).Two strains showed HM phenotype.PCR results showed that 90.5％ (76/84) of the strains were positive for blaKPC-2,1.2％ (1/84) positive for blaNDM and blaIMP each,but either blaOXA or blaVIM was not identified.The overall prevalence of virulence genes was low except for mrkD (97.6％,82/84),ybtS (92.9％,78/84) and entB (100％,84/84).Eight sequence types (STs) were obtained.The dominant clone was ST11 (84.5％,71/84),and the two strains of HM phenotype were ST11.eBURST analysis identified 2 ST groups among the 84 CRKPs.Each ST group includes 2 ST types (ST11 and ST1869,ST15 and ST709),respectively.The other four ST types were single ST type.In this study,71 strains of ST11,4 ST15 and 4 ST323 belonged to CC258,CC15 and CC163 clones,respectively.Conclusions CRKP is highly resistant to the commonly used antibiotics.The multidrug resistance or pandrug-resistance of K.pneumoniae is mainly associated with the expression of blaKPC-2 gene.Three virulence genes mrkD,ybtS and entB are highly prevalent in the CRKP isolates.The dominant clone of KPC-producing K.pneumoniae is ST11 in both hospitals.

Performance assessment of MALDI SepsityperTM kit and serum separator tube as pretreatment methods for direct identification of microorganisms from blood cultures using MALDI-TOF mass spectrometry / 中国感染与化疗杂志

Objective The aim of this study was to evaluate the commercial SepsityperTM kit and serum separator tube coupled with matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry for direct identification of microorganisms in a blood culture system.Methods A total of 138 clinical blood samples from clinical laboratory in Renji hospital were tested with two methods respectively from April to June of 2016.Performance of the assays were compared against that of conventional bacterial culture as a reference.Results A total of 138 nonduplicate positive blood culture samples were collected,including 70 (53.03％) gram negative samples,57 (43.18％) gram positive samples,3 fungus samples,2 mixed samples,and 6 false positive samples which were excluded from further analysis.The accuracy rate of SepsityperTM kit and serum separator tube was 91.67％ and 84.09％ in rapid identification of pathogen from blood samples,83.33％ and 61.36％ in correct identification to species level.The accuracy rate of SepsityperTM kit and serum separator tube was 98.57％ and 95.71％ in identifying gram-negative bacteria,87.72％ and 78.59％ in identifying gram-positive bacteria,respectively.The turnaround time for identification of each sample was 40 min by the commercial SepsityperTM kit and 25 min by serum separator tube.Conclusions MALDI SepsityperTM kit has shown slightly higher accuracy rate in identification of pathogen from blood sample than serum separator tube,but the difference is not significant (91.67％ vs.84.09％,P＞0.05).Compared with MALDI SepsityperTM kit,serum separator tube is a rapid,easy,and cost-effective pretreatment method for direct identification of microorganisms from blood cultures using MALDI-TOF mass spectrometry.

Molecular epidemiological analysis of Stenotrophomonas maltophilia strains in a teaching hospital in Shanghai / 中国感染与化疗杂志

Objective We evaluated the molecular epidemiology ofStenotrophomonas maltophilia strains in adult patients in Renji Hospital to Shanghai Jiao Tong University School of Medicine for better control ofS.maltophilia infections.Methods Nonduplicate clinical isolates of S.maltophilia were collected from Renji Hospital from January 2014 to September 2014.We examined the clonality among the S.maltophilia isolates by multilocus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).Antimicrobial resistance pattern was investigated by Kirby-Bauer method and prevalence of toxin genes (Stmpr1,Stmpr2,stmr-1,Smlt3773locus) by PCR.We also studied the biofilm formation of S.maltophilia by semiquantitative biofilm formation test.Results A total of 78 nonduplicate S.maltophilia isolates were analyzed,of which 26 were isolated from surgical intensive care unit,and 53 strains were from male patients.All patients infected by S.maltophilia had received antibiotic therapy before the strains were isolated.At least three kinds of antibiotics were used in 62.8％ of the patients.MLST analysis indicated that 49 isolates were assigned novel STs(STnewl-STnew38),with new combinations of allelic profiles.The largest cluster of isolates was ST23 (6 strains).PFGE showed that there was weak genetic linkage between S.maltophilia strains.The 78 isolates were divided into 58 groups.About 2.6％ (2/78) and 10.3％ (8/78) of these strains were resistant to levofloxacin and trimethoprim-sulfamethoxazole,respectively.All the strains were susceptible to minocycline.The prevalence of virulence genes Stmprl,Stmpr2,snf-1 and Smlt3773 locus was 79.5％ (62/78),93.6％ (73/78),94.9％ (74/78) and 48.7％ (38/78),respectively.Biofilm formation test indicated that the mean ability of biofilm formation was 0.51±0.44 in terms of D492.There was no significant difference between males and females.Conclusions All patients with Stenotrophomonas maltophilia infection had a history of antibiotic use and male patients were susceptible population.Stenotrophomonas maltophilia isolates showed high prevalence of virulence genes.No clonal dissemination was found in the same department of hospital.

Application of MALDI-TOF MS technology in the typing of pathogenic microorganisms / 中华检验医学杂志

Accurate, fast and sensitive typing of pathogenic microorganisms is very important for tracing the source of dissemination, defining the route of transmission, understanding the relationship between strains and clinical symptoms, exploring the pathogenic mechanism,guiding clinical therapy, etc.In recent years, matrix assisted laser desorption/ionization time of flight mass spectrometry(MALDI-TOF MS) has played an increasingly important role in the microbial identification, drug resistance and virulence study because of its rapidity, accuracy, good repeatability, high throughput etc.The new microbial typing method-MALDI-TOF MS fingerprint typing appears afterwards.This typing method is characterized by high throughput, rapidity, easy standardization and low cost, and it has promising application prospect in the areas such as epidemiological analysis of pathogenic microorganism, hospital infection control and development of biological markers.