Metallo-β-Lactamases:A Major Threat to Human Health

Antibiotic resistance is one of the most significant challenges facing global healthcare. Since the 1940s, antibiotics have been used to fight infections, initially with penicillin and subsequently with various derivatives including cephalosporins, carbapenams and monobactams. A common characteristic of these antibiotics is the four-memberedβ-lactam ring. Alarmingly, in recent years an increasing number of bacteria have become resistant to these antibiotics. A major strategy employed by these pathogens is to use Zn(II)-dependent enzymes, the metallo-β-lactamases (MBLs), which hydrolyse theβ-lactam ring. Clinically useful MBL inhibitors are not yet available. Consequently, MBLs remain a major threat to human health. In this review biochemical properties of MBLs are discussed, focusing in particular on the interactions between the enzymes and the functionally essential metal ions. The precise role(s) of these metal ions is still debated and may differ between different MBLs. However, since they are required for catalysis, their binding site may present an alternative target for inhibitor design.

Metallo-β-lactamase producing nonfermentative gram-negative bacteria:An increasing clinical threat among hospitalized patients

Objective:To detect and evaluate the various methods for metallo-β-lactamases(MBL) production in Pseudomonas aeruginosa(P.aeruginosa) and Acinetobacter species.Methods:A total of 109 P.aeruginosa and 85 Acinetobacter species were screened for imipenem resistance by Kirby- Bauer disc diffusion methods.Detection of MBL production was(lone by imipenem-EDTA combined disc test,double disc synerygy test(DDST) and imipenem-EDTA MBL E test.Results: A total of 63(57.8%) strains of P.aeruginosa and 46(54.1%) strains of Acinetobacter spp.were found to be resistant to imipenem.Of the 63 imipenem resistant P.aeruginosa tested for MBL production.44(69.89;) were found to be positive and among 46 imipenem resistant Acinetobacter. 19(41.3%) were shown to be the MBL producers.Conclusions:Imipenem-EDTA combined disc test and MBL E test are equally effective for MBL detection in both P.aeruginosa and Acinetobacter spp.,but given the cost-constraints,combined disc can be used as a convenient screening method in the clinical microbiology laboratory.

Prevalence and Antimicrobial Susceptibility Profile of Metallo-<i>β</i>-Lactamase Producing <i>Pseudomonas aeruginosa</i>Isolates at Kenyatta National Hospital

Pseudomonas aeruginosa is a major cause of nosocomial infections with high mortality rates. The organism is highly resistant to most classes of drugs used and can develop resistance during treatment. One of the resistance mechanisms of P. aeruginosais is Metallo-β-Lactamase (MBL) production. MBL producing P. aeruginosa is a major health concern given it’s resistance to almost all available drugs. The prevalence of this resistant strain is unknown since there is no standardized method for testing MBL production. This was a laboratory based cross-sectional prospective study that was carried out from September 2015 to March 2016 at Kenyatta National Hospital. Ninety-nine isolates of P. aeruginosa were collected during the period and tested for antimicrobial susceptibility and isolates found to be resistant to imipenem tested for MBL production. The results indicated high resistance of P. aeruginosa to commonly used drugs. Of the isolates tested 69.7% were resistant to piperacillin, 63.6% were resistant to aztreonam, 58.6% were resistant to levofloxacin, 55.6% were resistant to cefipime, 65.7% were resistant to ceftazidime, 68.7% were resistant to ticarcillin-clavulanate, 72.2% were resistant to meropenem, 64.9% were resistance to imipenem while 86.4% of urine isolates were resistant to ofloxacin. Of the isolates resistant to imipenem 87.3% were found to be MBL producers. In conclusion, P. aeruginosais highly resistant to the drugs currently is used for treatment and resistance to carbapenems is largely due to MBL production.

Evaluation of Disk Potentiation Test (DPT) and Double Disk Synergy Test (DDST) for The Detection of Metallo-β-Lactamases (MBLs) in Clinical Isolates of Bangladesh

Objective: Increasing the emergence of Metallo-β-lactamase (MBL) producing gram-negative bacteria and their dexterous horizontal transmission demands rapid and accurate detection. This study was conducted to determine a suitable method to promptly detect MBL-producing gram-negative bacteria. Methods: A total of 103 gram-negative bacteria were identified from various clinical samples at a tertiary care hospital in Dhaka city. MBL producers were detected by two phenotypic methods, the Disk Potentiation Test (DPT) and the Double Disk Synergy Test (DDST) based on β-lactam chelator combinations where EDTA/SMA has been used as an inhibitor and Imipenem, Ceftazidime as substrates. Results: 103 isolates which were identified as Escherichia coli spp, Klebsiella spp, Pseudomonas spp, Acinetobacter spp, Proteus spp, Providencia spp were found to be multidrug-resistant in antibiogram test. Isolates showed complete resistance (100%) to Imipenem, Meropenem, and Amoxiclav. The highest carbapenem-resistant etiological agents were Acinetobacter spp 40 (38.8%) followed by Pseudomonas spp 27 (26.2%), Klebsiella spp 26 (25.2%), Escherichia coli 8 (7.8%), Proteus spp 1 (1%) and Providencia spp 1 (1%). DPT method detected significantly (p = 0.000009) a higher number of MBL-producers (Imipenem with 0.5 M EDTA n = 61, 59.2% & Ceftazidime with 0.5 M EDTA n = 56, 54.4%) compared to the DDST method (Imipenem -0.5 M EDTA n = 43, 41.7%, Imipenem – SMA n = 38, 36.9% & Ceftazidime -0.5 M EDTA n = 15, 14.6%). Conclusion: Pieces of evidence suggest that DPT is a more sensitive method than DDST and could be recommended for identifying MBL-producing bacteria in Bangladeshi hospitals for the proper management of patients, to reduce time constraints and treatment costs.

Identification and preliminary characterization of novel B3-type metallo-β-lactamases

Antibiotic resistance has emerged as a major global threat to human health. Among the strategies employed by pathogens to acquire resistance the use of metallo-β-lactamases (MBLs), a family of dinuclear metalloenzymes, is among the most potent. MBLs are subdivided into three groups (i.e. B1, B2 and B3) with most of the virulence factors belonging to the B1 group. The recent discovery of AIM-1, a B3-type MBL, however, has illustrated the potential health threat of this group of MBLs. Here, we employed a bioinformatics approach to identify and characterize novel B3-type MBLs from Novosphingobium pentaromativorans and Simiduia agarivorans. These enzymes may not yet pose a direct risk to human health, but their structures and function may provide important insight into the design and synthesis of a still elusive universal MBL inhibitor.

Unusual metallo-β-lactamases may constitute a new subgroup in this family of enzymes

Metallo-β-lactamases (MBLs) are a family of Zn2+-dependent enzymes that have contributed strongly to the emergence and spread of antibiotic resistance. Novel members as well as variants of existing members of this family are discovered continuously, compounding their threat to global health care. MBLs are divided into three subgroups, i.e. B1, B2 and B3. The recent discovery of an unusual MBL from Serratia proteamaculans (SPR-1) suggests the presence of an additional subgroup, i.e. B4. A database search reveals that SPR-1 has only one homologue from Cronobacter sakazakii, CSA-1.These two MBLs have a unique active site and may employ a mechanism distinct from other MBLs, but reminiscent of some organophosphate-degrading hydrolases.

Virulence Factors and Biofilm Formation in Multidrug-Resistant Metallo-β-Lactamase-Producing Clinical Strains of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram-negative bacterium, responsible for nosocomial infections, with a complex arsenal of pathogenicity. The aim of this study was to simultaneously characterize the potential for resistance, virulence and biofilm formation in clinical strains. A total of 104 clinical P. aeruginosa strains (blood (26), stools (26), pus (26) and urine (26) were the subject of this study. The Mueller-Hinton diffusion method, agglutination test and combined disk diffusion test respectively made it possible to phenotypically determine the resistance profile, serogroups and metallo-β-lactamase production. Virulence, resistance and biofilm formation supports were detected by PCR. P. aeruginosa strains were resistant to aztreonam (76.4%), ticarcillin (62.4%), piperacillin (32.4%), imipenem (17.1%), cefepime (14%) and Ceftazidime (8.3%). The serogroups O11 (22.1%), O7 (18.3%), O16 (16.3%), and O9 (14.4%) were mainly determined in clinical strains. The total prevalence of metallo-β lactamase genes was 12.5% (blaIMP) and 11.5% (blaVIM). In descending order, the virulence genes exoS (55.8%), plcH (48.1%), LasB (47.1%), pilB (42.3%) and algD (41.3%) were detected (p pelA (28.8%) and pslA (23.1%). In conclusion, this study highlights the significant resistance, virulence, and biofilm-forming capabilities of clinical Pseudomonas aeruginosa strains. By profiling 104 strains, we found high resistance rates to multiple antibiotics, with notable serogroups and a considerable prevalence of metallo-β-lactamase genes, which pose a challenge for treatment. Additionally, key virulence genes and biofilm-associated genes were prevalent, underscoring the pathogenic potential of these strains. These findings underscore the importance of characterizing pathogenicity factors as a valuable strategy for monitoring and managing P. aeruginosa infections, especially in healthcare settings where such infections are common and difficult to treat.

IMB-XH1 identified as a novel inhibitor of New Delhi metallo-β-lactamase-1

The problem of drug resistance of Gram-negative bacteria has become increasingly serious and has aroused widespread public concern.The "super bacteria" producing New Delhi metallo-beta-lactamase(NDM-1) are resistant to almost all β-lactam antibiotics.However, clinically existing β-lactamase inhibitors are ineffective against metallo-β-lactamases(MBLs) including NDM-1.Therefore, effective NDM-1 inhibitors are urgently needed.In this study, a high-throughput screening model for NDM-1 inhibitors was optimized and used to screen NDM-1 inhibitors.As a result, IMB-XH1 was screened out as a novel NDM-1 inhibitor from 52 100 compounds of different sources.The combined use of IMB-XH1 can increase the sensitivity of E.coli BL21(DE3)(pET-30 a(+)-NDM-1) to β-lactam antibiotics.Enzymatic kinetic studies indicate that IMB-XH1 is a non-competitive inhibitor of NDM-1 and also has inhibitory activity against other MBLs such as IMP-4, ImiS and L1.As a novel NDM-1 inhibitor, its activity and mechanism of action need to be further explored.

New Delhi Metallo-β-Lactamase-Mediated Carbapenem Resistance： Origin, Diagnosis, Treatment and Public Health Concern

Objective： To review the origin, diagnosis, treatment and public health concern of New Delhi metallo-β-lactamase （NDM）-producing bacteria. Data Sources： We searched database for studies published in English. The database of PubMed from 2007 to 2015 was used to conduct a search using the keyword term ＂NDM and Acinetobacter or Enterobacteriaceae or Pseudomonas aeruginosa.＂ Study Selection： We collected data including the relevant articles on international transmission, testing methods and treatment strategies of NDM-positive bacteria. Worldwide NDM cases were reviewed based on 22 case reports. Results： The first documented case of infection caused by bacteria producing NDM- 1 occurred in India, in 2008. Since then, 13 blaNDM variants have been reported. The rise of NDM is not only due to its high rate of genetic transfer among unrelated bacterial species, but also to human factors such as travel, sanitation and food production and preparation. With limited treatment options, scientists try to improve available therapies and create new ones. Conclusions： In order to slow down the spread of these NDM-positive bacteria, a series of measures must be implemented. The creation and transmission of blaNDM are potentially global health issues, which are not issues for one country or one medical community, but for global priorities in general and for individual wound care practitioners specifically.

Dissemination of carbapenem-non-susceptible Acinetobacter baumannii isolates collected from educational hospitals in Qazvin province of Iran

Background:Acinetobacter baumannii(A.baumannii)is known as an opportunistic pathogen related to health-care-associated infection that has a high antibiotic resistance potential,notably against carbapenems that are widely used to combat A.baumannii infections.This study aimed to detect oxacillin-hydrolyzing(OXA)carbapenemases and metallo-β-lactamases(MBL)among carbapenem-resistant A.baumannii isolated strains and to determine their clonal relationship by repetitive extragenic palindromic PCR(rep-PCR).Methods:In the present study,a total of 211 non-repetitive isolates of A.baumannii were collected from Qazvin educational hospitals(2016–2017).The disk diffusion method was used to investigate the antibiotic susceptibility of studied strains,followed by the detection of MBL and OXA-type genes using polymerase chain reaction(PCR)and sequencing methods.The rep-PCR method assessed the clonal relationship of carbapenem-non-susceptible A.baumannii isolates.Result:The obtained results showed that 87.2%and 86.7%of isolates were non-susceptible to imipenem and meropenem.The blaOXA-24(93.5%)was the most frequent gene,followed by the blaOXA-23(4.34%),blaIMP-1(1.63%),and blaVIM-1(0.54%).Meanwhile,blaOXA-58 and blaOXA-143 genes were not found.81.5%and 66.1%of isolates contained ISAba1 upstream of the blaOXA-23 and blaOXA-58 genes,respectively.Rep-PCR results revealed the carbapenem non-susceptible isolates belonged to three distinct clones:A 171(81%),B 34(16.1%),and C 6(2.8%).Conclusions:The results indicated a high prevalence of carbapenem-non-susceptible A.baumannii,with the emergence of the blaOXA-24 gene as the most common gene and the notable prevalence of MBL genes.These results revealed the need for appropriate therapeutic and infection control strategies and monitoring susceptibility patterns for controlling A.baumannii infections.

Activation free energy of Zn(Ⅱ),Co(Ⅱ) binding to metallo-β-lactamase ImiS

In an effort to understand the recombination of a B2 metallo-β-lactamase（MβL）,the binding of metals to apo-ImiS was studied by isothermal titration calorimetry and fluorescence spectra.The binding of Zn（Ⅱ）,Co（Ⅱ） to apo-lmiS resulted in activation free energies △G_≠~θ values of 93.719 and 92.948 kJ mol^（-1）,respectively,and increasing of fluorescence intensity at maxima emission of 340 nm.

Spreading of extended-spectrum β-lactamase-producing Escherichia coli ST131 and Klebsiella pneumoniae ST11 in patients with pneumonia a molecular epidemiological study

Background: Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) are the important pathogens causing pneumonia. This study aimed to investigate the clinical characteristics and molecular epidemiology of ESBL-producing E. coli and K. pneumoniae causing pneumonia at a large teaching hospital in China. Methods: We collected patient's clinical data and ESBL-producing E. coli and K. pneumoniae strains causing pneumonia (from December 2015 to June 2016) at a hospital in Wuhan. The susceptibilities, multi-locus sequence typing, homologous analysis, ESBL genes by polymerase chain reaction and sequencing were determined. Results: A total of 59 ESBL-producing strains (31 E. coli and 28 K. pneumoniae) isolated from patients with pneumonia were analyzed. The majority of strains were isolated from patients were with hospital-acquired pneumonia (37/59, 62.7%), followed by community-acquired pneumonia (13/59, 22.0%), and ventilator-related pneumonia (9/59, 15.3%). The E. coli ST131 (9 isolates, 29.0%) and K. pneumoniae ST11 (5 isolates, 17.9%) were the predominant sub-types. The most prevalent ESBL gene was CTX-M-14, followed by SHV-77, CTX-M-3, SHV-11, and CTX-M-27. At least 33 (55.9%) of the ESBL-producing strains carried two or more ESBL genes. The ISEcp1 and IS26 were found upstream of all blaCTX-M (CTX-Ms) and of most blaSHV (SHVs)(57.6%), respectively. Moreover, three ESBL-producing K. pneumoniae ST11 strains which were resistant to carbapenems carried the blaNDM-1 and blaKPC-2, two of which also bearing blaOXA-48 were resistant to all antibiotics (including Tigecycline). Conclusions: Hospital-acquired pneumonia is more likely correlated with ESBL-producing E. coli and K. pneumoniae. ESBL-producing E. coli ST131 and multi-drug resistance ESBL-producing, as well as New Delhi metallo-β-lactamase-1 (NDM-1) and Klebsiella pneumoniae carbapenemases-2 (KPC-2) bearing K. pneumoniae ST11 are spreading in patients with pneumonia in hospital.

Drug-resistant genes carried by Acinetobacter baumanii isolated from patients with lower respiratory tract infection

Background Acinetobacter baumanii （A. baumanii ） remains an important microbial pathogen resulting in nosocomialacquired infections with significant morbidity and mortality. The mechanism by which nosocomial bacteria, like A. baumanii, attain multidrug resistance to antibiotics is of considerable interest. The aim in this study was to investigate the spread status of antibiotic resistance genes, such as multiple 13-1actamase genes and aminoglycoside-modifying enzyme genes, from A. baumanii strains isolated from patients with lower respiratory tract infections （LRTIs）. Methods Two thousand six hundred and ninety-eight sputum or the bronchoalveolar lavage samples from inpatients with LRTIs were collected in 21 hospitals in the mainland of China from November 2007 to February 2009. All samples were routinely inoculated. The isolated bacterial strains and their susceptibility were analyzed via VITEK-2 expert system. Several kinds of antibiotic resistant genes were further differentiated via polymerase chain reaction and sequencing methods. Results Totally, 39 A. baumanii strains were isolated from 2698 sputum or bronchoalveolar lavage samples. There was not only a high resistant rate of the isolated A. baumanfi strains to ampicillin and first- and second-generation cephalosporins （94.87%, 100% and 97.44%, respectively）, but also to the third-generation cephalosporins （ceftriaxone at 92.31%, ceftazidine at 51.28%） and imipenem （43.59%） as well. The lowest antibiotic resistance rate of 20.51% was found to amikacin. The OXA-23 gene was identified in 17 strains of A. baumanii, and the AmpC gene in 23 strains. The TEM-1 gene was carried in 15 strains. PER-1 and SHV-2 genes were detected in two different strains. Aminoglycoside-modifying enzyme gene aac-3-1a was found in 23 strains, and the aac-6＂lb gene in 19 strains, aac-3-1a and aac-6＂lb genes hibernated in three A. baumanfi strains that showed no drug-resistant phenotype. Conclusions A. baumanii can carry multiple drug-resistant genes at the same time and result in multi-drug resistance. Aminoglycoside-modifying enzyme genes could be hibernating in aminoglycoside sensitive strains without expressing their phenotype.

Detection and Characterization of β-Lactam Resistance in Haemophilus parasuis Strains from Pigs in South China

To characterize the β-lactam resistance in veterinary clinical isolates of Haemophilus parasuis, 115 isolates were examined for the β-lactam resistance, the possession of β-lactamase, and the presence of β-lactamase genes. The genetic relationship among isolates was evaluated by pulsed-field gel electrophoresis （PFGE）. Overall, the commonly detected resistance phenotypes were resistant to ampicillin （26.09%）, penicillin （22.61%）, amoxicillin （21.74%）, cefazolin （14.78%）, cefaclor （12.17%）, and cefotaxime （6.96%）. These strains showed high minimal inhibitory concentration （MICs） to oxacillin. 20.87% strains produced β-lactamase, and 4.35% strains showed extended-spectrum b-lactamase （ESBL） phenotype. Moreover, 19 strains harboured bla genes including TEM-1 （n=5）, TEM-116 （n=10）, and ROB-1 （n=5）. Significantly, one strain possessed both TEM-1 and ROB-1, and displayed resistance to cefotaxime （MIC=8 mg L-1）. The epidemiological analysis of PFGE revealed high genetic diversity among bla-positive isolates. This work shows that TEM- and ROB-type β-lactamases are prevalent in H. parasuis isolates in China.

Drug resistance of infectious pathogens after liver transplantation

BACKGROUND: Infection in liver recipients is related to high risk of transplantation failure and mortality. Infectious agents isolated from 55 liver recipients from January 2003 through June 2005 were studied to improve the anti-infectious therapy. METHODS: Pathogens were isolated from routine culture. K-B method was used to examine the drug susceptibility. Extended spectrum β-lactamase, AmpC β-lactamase and Van gene in E. coli were examined by the agar-dilution susceptibility test and Nitrocefin test. RESULTS: Thirty-nine of the 55 recipients got infection. The 513 strains of pathogens isolated from 1861 specimens were predominantly Gram negative bacteria and over 40% of them showed resistance to more than 4 drugs. The positive rates of extended spectrum β-lactamse and AmpC β-lactamse production in E. cloacae were 32.4% and 36.8%, in E. coli were 33.8% and 10.5%, but the rates of these 2 bacteria producing both lactamses were 24.3% and 7.0%. The β-lactamse production rates of Enterococcus faecalis and En-terococcus faecium were 8.8% and 11.1%, and the resistance rates to vancomycin were 11.2% and 18.5%, respectively. CONCLUSIONS: Infectious pathogens isolated from liver recipients are potent and multiple drug resistant. ESBLs and AmpC β-lactamases are the major factors associated with Gram negative drug resistance. The infection of En-terococcal species presents as a particular challenge.

An unexpected similarity between antibiotic-resistant NDM-1 and beta-lactamaseⅡfrom Erythrobacter litoralis

NDM-1(New Delhi metallo-beta-lactamase)gene encodes a metallo-beta-lactamase(MBL)with high carbapenemase activity,which makes the host bacterial strain easily dispatch the last-resort antibiotics known as carbapenems and cause global concern.Here we present the bioinformatics data showing an unexpected similarity between NDM-1 and beta-lactamase II from Erythrobacter litoralis,a marine microbial isolate.We have further expressed these two mature proteins in E.coli cells,both of which present as a monomer with a molecular mass of 25 kDa.Antimicrobial susceptibility assay reveals that they share similar substrate specificities and are sensitive to aztreonam and tigecycline.The conformational change accompanied with the zinc binding visualized by nuclear magnetic resonance,Zn2+-bound NDM-1,adopts at least some stable tertiary structure in contrast to the metal-free protein.Our work implies a close evolutionary relationship between antibiotic resistance genes in environmental reservoir and in the clinic,challenging the antimicrobial resistance monitoring.

Insights on the structural characteristics of NDM-1: The journey so far

New Delhi metallo-β-lactamase (NDM-1) has created a medical storm ever since it was first reported;as it is active on virtually all clinically used β-lactam antibiotics. NDM-1 rampancy worldwide is now considered a nightmare scenario, particularly due to its rapid dissemination. An underlying theme in the majority of recent studies is structural characterization as knowledge of the three-dimensional structure of NDM-1 shall help find connections between its structure and function. Moreover, structural details are even critical in order to reveal the resistance mecha- nism to β-lactam antibiotics. In this perspective, we review structural characteristics of NDM-1 that have been delineated since its first report. We anticipate that these structure-function connections made by its characterization shall further serve as future guidelines for elucidating pathways towards de novo design of functional inhibitors.

Phenotypic and genotypic detection of extended-spectrum β-lactamase (ESBL) producing Escherichia coli isolated from urinary tract infections in Zabol,Iran

Objective:To investigate the role of a rapid polymerase chain reaction(PCR)assay in comparison with traditional empiric therapy in detection of extended spectrum β-lactamase(ESBL)producer Escherichia coli(E.coli).Methods:Ninety isolates of E.coli from urinary tract infection were collected and screening of ESBL resistance using disc diffusion method,minimum inhibitory concentration(MIC)for ceftazidime and detection of TEM resistant gene by PCR were done.Results:The results of disc diffusion method showed that forty out of ninety E.coli isolates were ESBLs producing organisms.Antibiotic susceptibility of E.coli isolates to 9 antibacterial agents were evaluated.However,all isolated E.coli were resistant to all 9 antibacterial agents by these percentage:ceftriaxon(100%),ceftazidime(100%),amoxicillin(100%),erythromycin(100%),azithromycin(95%),cefixime(87.5%),tetracyclin(87.5%),nalidixic acid(85%)and difloxcain(75%).The abundance of antibiotic-resistant TEM gene according to PCR was 30%.Totally 82.5%of strains tested by MIC were observed as ceftazidime-resistant.Conclusions:We conclude that the TEM gene PCR assay is a rapid,sensitive and clinically useful test,particularly for the early detection of ESBLs-producing E.coli.

The Increased Frequency of Carbapenem Resistant Non Fermenting Gram Negative Pathogens as Causes of Health Care Associated Infections in Adult Cancer Patients

Background and Aim: Multi drug resistant Non fermenting gram negative bacilli (NFGNB) have emerged as a major cause of health-care associated infections especially in immunocompromised hosts. The aim of the study was to investigate the prevalence of NFGNB as a cause of health-care associated infections (HAI) in cancer patients and determine their resistance pattern. Patients and Methods: During the study period, 158 NFGNB isolates were collected. Microscan Walk Away 9 was used for identification and testing for the metallo-β-lactamases (MBLs) was done by Imipenem-EDTA combined disk synergy test (CDST-IPM). Results: NFGNB represented 29.0% of infections caused by gram negative organisms. Carbapenem resistance, the multi-drug resistant (MDR) phenotype, and MBL production were documented in 70%, 63%, and 59% of NFGNB isolates, respectively. MDR-NFGNB rates were significantly higher among hospitalized patients, medical department and those with longer duration of hospital stay (p = 0.034, 0.026, 0.019;respectively) than non MDR-NFGNB. Conclusion: A high level of carbapenem and multi-drug resistance were detected among the non-fermenter pathogens isolated from hospitalized cases and were more frequently encountered in high risk adult cancer patients requiring longer duration of hospitalization. The MDR-NFGNB are constituting important causes of health-care associated infections in cancer patients.

Characterization of multidrug-resistant and metallo-beta- lactamase-producing Pseudomonas aeruginosa isolates from a paediatric clinic in China

Background In the present study, we characterized multidrug-resistant Pseudomonas aeruginosa （MDRP） clinical isolates from a paediatric facility and investigated the types and features of the metallo-β-lactamases （MBLs） produced by carbapenem-resistant strains. Methods Four hundred and ninety-eight strains of Pseudomonas aeruginosa were isolated from patients at Beijing Children＇s Hospital between January 2005 and December 2006. The minimal inhibition concentrations （MICs） of the strains for 13 antibiotics were measured. A combination of the E test and PCR amplification/DNA sequencing was used to define the carbapenem-resistant strains. Results We found that 24.1% （120/498） of the isolates were MDRP. The frequencies of resistance to imipenem and meropenem were 34.2% and 35.8%, respectively, and the MIC50 and MIC90values for the two antibiotics were identical at 4 pg/ml and 32 pg/ml, respectively. The detection rate for carbapenem resistance was 49.2% （59/120）. Among the 59 carbapenem-resistant Pseudomonas aeruginosa strains, 39 （66.1%） were positive for the MBL genotype; 35 （89.7%） strains carried the blaiMp gene and 4 （10.3%） strains carried the blavm gene. Neither blasPM nor blaGiM was amplified from any of the 59 isolates. DNA sequencing revealed that IMP-1 was present in 35 IMP-producing isolates and VIM-2 was detected in four VIM-producing isolates. Conclusions These MDRP isolates exhibited high frequencies of resistance to carbapenems among clinical isolates from a paediatric facility in Beijing, China. The production of MBL appears to be an important mechanism for carbapenem resistance in Pseudomonas aeruginosa.