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Antimicrobial susceptibility of 9 strains of carbapenemase-producing Klebsiella pneumoniae

Ying JIN ; Junfang WANG ; Jiqin LIU ; Xin ZHOU

Chinese Journal of Infection and Chemotherapy.2015;(3):257-259.

Objective To analyze the resistant profile and genotypes ,as well as susceptibility to tigecycline in carbapenemase‐producing K lebsiella pneumoniae for better clinical management of such infections .Methods Nine strains of carbapenemase‐producing K .pneumoniae were isolated from clinical specimens during the period from February 2012 to May 2013 in our hospital .Bacterial identification and antimicrobial susceptibility testing were carried out with VITEK 2 Compact automatic microbiological assay systems .The phenotype of carbapenemase‐producing K . pneumoniae was detected by modified Hodges test .The genotype of carbapenemase was identified by PCR method .The susceptibility to tigecycline was tested by E‐test . Results All the 9 strains of carbapenemase‐producing K . pneumoniae were resistant to the 19 antibiotics tested .Modified Hodges test was positive for 7 strains (77 .8% ) .Target band of carbapenemase gene was identified in all the 9 strains of K . pneumoniae ,and all were confirmed as KPC‐2 gene .All the 9 strains were susceptible to tigecycline .Conclusions The resistance of carbapenemase‐producing K .pneumoniae is still serious .Tigecycline has shown good in vitro activity against such strains .

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Mechanism of carbapenem resistance in the Acinetobacter baumannii isolates from an intensive care unit

Pu MAO ; Jianchun LI ; Guixia QIU ; Dan YE ; Xiaoqing LIU ; Yimin LI

Chinese Journal of Infection and Chemotherapy.2015;(3):253-256.

Objective To explore the causes of rising carbapenem resistance in Acinetobacter baumannii isolates by analysis of the carbapenemase genotypes in A .baumannii .Methods WHONET 5 .4 was used to analyze the changing resistance profile of A .baumannii isolates over years .A total of 320 carbapenem‐resistant A .baumannii isolates were collected from the patients in an intensive care unit from January 2008 to December 2012 .All strains were identified and tested by VITEK 2 for their susceptibility .The metallo‐β‐lactamases genes and OXA carbapenemase genes were investigated by polymerase chain reaction . Results The resistance rate of A .baumannii isolates to meropenem and imipenem increased rapidly from 10 .8% to 80 .4% and from 13 .5% to 83 .5% during the period from 2008 and 2012 .The prevalence of blaOXA‐23and ISAba1‐associated blaOXA‐23genes increased from 25 .0% to 97 .1% .No metallo‐β‐lactamase encoding genes were detected .Conclusions Our results indicate that the rising carbapenem resistance in the A . baumannii isolates in our intensive care unit may be associated with the high prevalence of blaOXA‐23 and IS A ba1‐associated blaOXA‐23 genes .

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Surveillance of antimicrobial resistance of clinical bacterial isolates in a hospital during 2013

Rongfeng YAO ; Guoxiang XU ; Long XUE ; Juying SHEN ; Zhi LI ; Rong XIA ; Qiwen XIAO

Chinese Journal of Infection and Chemotherapy.2015;(3):244-248.

Objective To investigate the antibiotic resistance of clinical isolates from hospital for the guidance of rational use of antibiotics .Methods Automatic VITEK‐2 system was used to identify bacterial strains and analyze the antimicrobial resistance . WHONET 5 .6 was applied for data analysis according to the breakpoints of Clinical and Laboratory Standards Institute 2013 . Results A total of 3 880 nonduplicate strains were collected in 2013 ,35 .2% (1 366/3 880) of which were gram positive organisms ,64 .8% (2 514/3 880) were gram negative bacteria .The top 6 most frequently isolated microorganisms were E . coli (20 .2% ) , K . pneumoniae (12 .0% ) , P . aeruginosa (11 .1% ) , coagulase negative Staphylococcus (9 .8% ) , A . baumannii (9 .8% ) ,E .f aecalis (8 .1% ) .The bacteria were mainly isolated from respiratory tract (51 .0% ) ,urine (26 .2% ) , and blood (9 .4% ) .The prevalence of both meticillin‐resistant Staphylococcus was higher than 72 .0% .No staphylococcal strainwasfoundresistanttolinezolid,vancomycinortigecycline.Amongthe509Enterococcusisolates,E.faecalisandE. f aecium accounted for 61 .5% and 32 .8% ,respectively .No enterococcal strain was resistant to vancomycin or tigecycline . Enterococcal isolates also showed low resistance (<2 .0% ) to teicoplanin and linezolid .About 67 .4% of the E .coli strains and 32 .0% of the K lebsiella isolates produced extended spectrumbeta‐lactamases.Thestrainsof E.coli,Klebsiella spp.,Enterobacterspp.,and Proteusspp.wererelatively susceptible to beta‐lactam/beta‐lactamase inhibitor combinations such as cefoperazone‐sulbactam and piperacillin‐tazobactam , carbapenems such as meropenem ,imipenem and ertapenem ,and amikacin (< 15 .0% of the strains were resistant) . K . pneumoniae isolates were more resistant than other gram‐negative bacilli .P .aeruginosa was relatively susceptible to amikacin , tobramycin ,cefepime ,gentamicin ,piperacillin‐tazobactam ,but more than 20% of these strains were resistant to meropenem and imipenem .More than 35 .0% of the A . baumannii isolates were resistant to any of the antimicrobial agents tested . Conclusions Antimicrobial resistance is still a serious threat in clinical antimicrobial therapy .It is important to promote the rational use of antimicrobial agents so that resistance is minimized . It is necessary to conduct epidemiological survey and proactively implement effective interventions in the clinical setting with relatively heavy burden of antimicrobial resistance .

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Pathogenic bacteria and drug resistance in 132 cases of peritoneal dialysis related peritonitis

Hong DAI ; Jilu SHEN ; Boke ZHANG ; Yonggui WU ; Wen LU ; Xingming XU

Chinese Journal of Infection and Chemotherapy.2015;(3):236-243.

Objective To investigate the pathogens and their antibiotic resistance in patients with peritoneal dialysis‐related peritonitis .Methods The clinical data including pathogens ,antibiotic resistance profile of 213 patients with peritoneal dialysis‐related peritonitis who were treated in our peritoneal dialysis center from January 2011 to December 2013 were analyzed retrospectively .Results Dialysate culture was positive for 132 (62 .0% ) of the 213 cases ,resulting in a total of 140 strains of microorganisms ,including 84 strains of gram positive cocci ,37 strains of gram‐negative bacilli ,10 strains of fungus and 9 strains of gram positive bacilli . Coagulase‐negative Staphylococcus was the most common gram positive bacteria while Escherichia coli was the most common gram negative bacteria isolated from the effluent .The prevalence of methicillin‐resistant S .aureus and methicillin‐resistant coagulase negative Staphylococcus was 14 .3% (1/7) and 43 .2% (19/44) ,respectively . About 44 .4% (8/18) of the E .coli and K . pneumoniae isolates produced extended spectrum beta‐lactamases .All the gram‐positive cocci were sensitive to vancomycin and linezolid and slightly resistant to chloramphenicol (6 .3% ) , moxifloxacin (8 .5% ) , and rifampicin (9 .5% ) , but highly resistant to cefazolin (90 .0% ) ,followed by ampicillin (76 .7% ) ,oxacillin (71 .2% ) and penicillin (69 .7% ) . Coagulase negative Staphylococcus isolates were sensitive to vancomycin , linezolid , tigecycline , quinupristin‐dalfopristin and daptomycin ,but all resistant to cefazolin and ampicillin ,and highly resistant to penicillin (91 .9% ) and oxacillin (82 .5% ) .All the gram‐negative bacilli were sensitive to meropenem ,ertapenem ,cefoperazone‐sulbactam and tigecycline .About 80 .6% and 65 .5% of the gram‐negative bacilli were resistant to ampicillin and peperacillin ,respectively .E .coli isolates were sensitive to meropenem ,ertapenem and piperacillin‐tazobactam but highly resistant to ampicillin (81 .3% ) and piperacillin (71 .4% ) . Conclusions Gram‐positive cocci especially Staphylococcus and gram negative bacteria E .coli are major pathogens in peritoneal dialysis‐related peritonitis .Adequate microbiological culture and suitable antimicrobial therapy are key to successful treatment of the peritonitis associated with peritoneal dialysis .

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Distribution and antibiotic resistance of Klebsiella pneumoniae strains in terms of K1 and K2 serotypes

Rong MA ; Kefang LIU ; Daping NIE ; Ruihua LI

Chinese Journal of Infection and Chemotherapy.2015;(3):204-208.

Objective To investigate the distribution and antibiotic resistance of the K lebsiella pneumoniae strains isolated from clinical infections in terms of serotypes K1 ,K2 and virulence factor rmpA gene .Methods The hypermucoviscous phenotype of K .pneumoniae isolate was determined by string test .K1 and K2 serotypes and rmpA gene were detected using multiplex polymerase chain reaction .Results Of the 144 strains of K .pneumoniae ,the prevalence of hypermucoviscous phenotype ,K1 , K2 serotypes and rmpA gene was 62 .5% (90/144) ,52 .1% (75/144) and 65 .3% (94/144) ,respectively .The prevalence of K1 ,K2 and rmpA K .pneumoniae strains was 90 .7% (68/75) in K1 ,K2 serotypes .The prevalence of K1 ,K2 isolates and rmpA in hypermucoviscous or non‐hypermucoviscous phenoype was 63 .3% (57/90) ,85 .6% (77/90) and 33 .3% (18/54) , 31 .5% (17/54) ,respectively .The prevalence of serotype K1 ,K2 with or without rmpA gene was 72 .3% (68/94) and 14 .0% (7/50 ) respectively . Of the 42 K . pneumoniae strains isolated from liver abscess ,85 .7% (36/42) were hypermucoviscous phenotype and 88 .1% (37/42 ) were serotypes K1 , K2 . For the strains from other abscess , bacteremia ,community acquried pneumonia (CAP) ,urinary tract infection (UTI) and biliary tract infection ,the prevalence of hypermucoviscous phenotype was 81 .3% (13/16) ,40 .5%(15/37) ,85 .7% (12/14) ,52 .4% (11/21) and 21 .4% (3/14) ,respectively ,and the prevalence of serotypes K1 ,K2 was 56 .3% (9/16) ,29 .7% (11/37) ,64 .3% (9/14) ,38 .1% (8/21) and 7 .1% (1/14) ,respectively .K1 serotype isolate accounted for 61 .9% of the strains from liver abscess .The ratio between serotype K1 and K2 was similar in the isolates from other abscess ,CAP ,UTI or bacteremia .Non‐K1 ,K2 serotype isolates were common in biliary tract infection .The prevalence of extended‐spectrum beta‐lactamases (ESBLs ) was 5 .5% in hypermucoviscous phenotypes and 33 .3% in the non‐hypermucoviscous phenotypes .Conclusions rmpA gene is associated with the hypermucoviscous phenotype of K .pneumoniae strains and commonly identified in K1 ,K2 serotype isolates .Serotypes K1 ,K2 isolates are important pathogens in liver abscess and CAP ,and also common in other abscess ,UTI and bacteremia .K1 serotype isolate was most common in liver abscess .The prevalence of K1 or K2 serotype was similar in other infections . The prevalence of ESBLs is lower in hypermucoviscous strains than in non‐hypermucoviscous strains and is associated with lower resistance rate to most of the antibiotics tested .

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Study on efflux pump MexAB-OprM in carbapenem-resistant Pseudomonas aeruginosa

Guang WEI ; Ying YE ; Meijuan ZHENG ; Jilu SHEN

Chinese Journal of Infection and Chemotherapy.2015;(3):193-198.

Objective To study the relationship between efflux pump MexAB‐OprM and carbapenem resistance of Pseudomonas aerginosa strains .Methods The minimum inhibitory concentrations of imipenem and meropenem were determined by agar dilution method for 75 strains of P .aerginosa in the absence or presence of MC207110 to screen the phenotypes of active efflux pump .Reverse transcriptase‐polymerase chain reaction (RT‐PCR) method was used to determine the mRNA expression level of mexA which encodes the membrane fusion protein in active efflux pump MexAB‐OprM and the reference (housekeeping) gene rpoD .PCR method was used to amplify the regulatory genes mexR ,nalC ,and nalD of active efflux pump MexAB‐OprM in the strains overexpressing the efflux pump . The PCR products were subject to DNA sequencing and BLAST analysis . Results Of the 75 P .aeruginosa strains ,13 (17 .3% ) were positive for efflux pump MexAB‐OprM .Overexpression of the efflux pump was identified in 10 of the 13 strains and associated with positive regulatory genes mexR ,nalC and nalD .A Gly71→Glu mutation in nalC was found in 9 strains ,and a Ser209→Arg mutation in nalC was identified in 8 strains .Only one strain had a Thr158→Ile mutation in nalD .Eight strains had mutation in mexR .Conclusions Overexpression of multidrug efflux pump MexAB‐OprM plays an important role in carbapenem resistance of P .aeruginosa .High level expression of MexAB‐OprM is related to the mutations of its regulatory genes .

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Molecular epidemiological analysis of Streptococcus pyogenes strains isolated from the adult and pediatric patients in Shanghai,China

Haoqin JIANG ; Mingliang CHEN ; Tianming LI ; Hong LIU ; Mei ZENG ; Min LI

Chinese Journal of Infection and Chemotherapy.2015;(3):222-229.

Objective To investigate and compare the molecular epidemiological characteristics of Streptococcus pyogenes isolates from Shanghai adult and pediatric patients in terms of antimicrobial susceptibility ,clone type ,emm type ,biofilm formation and virulence for better infection control and treatment .Methods Thirty‐nine nonduplicate clinical isolates of S . pyogenes from adult and pediatric patients were analyzed by determining the susceptibility to antimicrobial agents by Kirby‐Bauer method;clonal typing by multilocus sequence typing ( MLST ); genotyping by emm gene sequence analysis ,which encoding M protein;genomic characteristics of different emm type strains by pulsed field gel electrophoresis (PFGE );and biofilm formation by semi‐quantitative biofilm formation test . Twenty main virulence genes of S .pyogenes ,including 12 superantigen genes and 8 other key genes were detected by PCR and gel electrophoresis . Results A total of 39 nonduplicate S .pyogenes isolates were analyzed .The most common genotype was emm 12‐ST36 (64 .1% ) and emm 1‐ST28 (17 .9% ) .Isolates from adult and pediatric patients had the same dominant genotype , emm 12‐ST36 . The isolates from children showed significantly higher resistance rate to erythromycin and clindamycin than those from adult patients (P<0 .000 1) .Particular emm type and clone type were frequently identified in the same PFGE cluster .Statistical analysis showed that biofilm formation was significantly associated with emm type 1 (P=0 .005) and erythromycin/clindamycin resistance (P=0 .000 3) .The strains from children showed higher biofilm formation than those from adult patients (P<0 .000 1) .We found that virulence genes speA ,speJ and spd3 were significantly associated with emm type 1 (P<0 .000 1 ,P=0 .005 5 ,P<0 .000 1) ,while speI and sic were significantly associated with emm type 12 (both P<0 .000 1) .We also found that the prevalence of speC ,speH ,ssa , smeZ ,and sdaD genes was significantly different between emm type 12 and emm type 1 (P= 0 .023 8 , P< 0 .000 1 , P<0.0001,P= 0.0003,and P= 0.0068,respectively).TheprevalenceofvirulencegenesspeH,smeZandsdaDwas significantly different between the emm type 12 strains from children and those from adults (all P< 0 .000 1) .Conclusions There is a strong agreement between emm type ,clone type ,virulence genes and the clusters defined by PFGE profiling of S . pyogenes .S .pyogenes isolates from adult and pediatric patients are different in terms of antibiotic resistance and biofilm formation .Certain emm type is significantly associated with antibiotic resistance and virulence ,which is useful for infection control .Dominant virulence genes may be the potential target for developing new vaccine to reduce S .pyogenes infection in the future .

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Fosfomycin resistance and f os gene detection in clinical St ap hy lococcus aureus strains

Zhuyingjie FU ; Shi WU ; Ying MA ; Yang YANG ; Dongfang LIN ; Fupin HU ; Demei ZHU ; Yang LIU ; Xiaogang XU

Chinese Journal of Infection and Chemotherapy.2015;(3):209-213.

Objective To understand fosfomycin resistance and prevalence of fos gene in clinical Staphylococcus aureus strains . Methods A total of 109 clinical strains of S .aureus were isolated from the patients in Huashan Hospital from January to March in 2014 .Antimicrobial susceptibility testing was performed by agar dilution method .The genes related to fosfomycin resistance including fosA ,fosB and fosC were detected by PCR .The flanking sequences of fos gene were determined by primer walking sequencing .The multilocus sequence typing (MLST) was carried out for fos gene positive strains .Results Forty‐four strains were resistant to fosfomycin (MIC> 32 mg/L) ,including 13 positive for fosB gene .Thirteen of the 109 (11 .9% ) strains carried fosB gene .However ,no fosA or fosC gene was identified .ST1 was a dominant MLST type in the strains carrying fosB gene .The three strains positive for fosB gene and associated with high level fosfomycin resistance (MIC> 512 mg/L) belonged to three different ST types . Walking sequencing showed that the fosB gene located on a transferable element containing a transposase gene .Conclusions High prevalence of f osB gene in fosfomycin‐resistant S . aureus strains indicates that f osB gene may mediate or contribute to fosfomycin resistance .

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Detection of methicillin-resistant S . aureus from respiratory specimens of ICU patients by conventional sputum culture compared with rapid polymerase chain reaction assay

Lei SHEN ; Jun LUO ; Hong SHI ; Hechen ZHU

Chinese Journal of Infection and Chemotherapy.2015;(3):260-263.

Objective To evaluate the performance of polymerase chain reaction (PCR)‐based rapid detection of methicillin‐resistant S .aureus (MRSA) from the respiratory specimens of ICU patients in comparison with conventional sputum culture . Methods We collected 3 respiratory specimens from each patient simultaneously for bacterial culture ,fungal culture and PCR‐based detection of MRSA .The performance of the established PCR method was compared with the results of sputum culture in terms of sensitivity ,specificity ,positive predictive value (PPV) and negative predictive value (NPV) .Results The sensitivity , specificity ,PPV and NPV of PCR assay were 88 .9% ,73 .6% ,36 .4% ,and 97 .5% ,respectively ,which were lower than the reported results of PCR assay with nasal swabs .Conclusions The utility of PCR assay for active screening of MRSA from respiratory specimens still needs further supportive data .However ,PCR assay is somewhat informative in excluding MRSA infection or colonization because of its high NPV .

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Distribution and antimicrobial resistance of the clinical strains isolated f rom the cervical secretions of parturient women

Qian WANG ; Chuan HUA ; Suli LI ; Yang LI

Chinese Journal of Infection and Chemotherapy.2015;(3):249-252.

Objective To investigate the distribution and antimicrobial resistance of clinical bacterial strains isolated from the cervical secretions of parturient women .Methods A total of 239 bacterial strains were isolated from 1 519 cervical specimens of parturient women .These strains were identified and tested by Kirby‐Bauer method for their susceptibility to antimicrobial agents .Results Escherichia coli was the most frequently isolated bacteria ,accounting for 34 .3% .The bacterial strains were more or less resistant to commonly used antimicrobial agents .Conclusions Various bacterial species are identified in the cervical secretions of parturient women ,primarily Escherichia coli and Staphylococcus aureus .Bacterial culture and antimicrobial susceptibility testing are important for clinicians to take appropriate measures to reduce the incidence of mother‐to‐child infections .

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