Clonal diversity of metallo-beta-lactamase-possessing Pseudomonas aeruginosa in geographically diverse regions of Japan

Classification of the metallo β-lactamase subtype produced by the carbapenem-resistant Pseudomonas aeruginosa isolates in Japan

INTRODUCTION

Multidrug resistant microorganisms are a serious threat to human health. Under the circumstances, a front line of antimicrobials in clinical setting may be carbapenem β-lactams (CRBP). However, emergence of CRBP resistant (CRBP-r) Gram-negative bacteria are the most alarming. CRBP-r is mainly caused to the production of β-lactamase, down and up expression of the diffusion channel and the efflux pump genes, respectively. Among them, production of metallo-β-lactamase (MBL) is a major cause of high-level of CRBP-r.

METHOD

We analyzed the MBL subtypes by PCR and DNA sequencing in CRBP-r Psudomonas aeruginosa in the collection of the joint program by the Japanese Association for Infectious Diseases, Japan Society for Clinical Microbiology and Japanese Society of Chemotherapy (2006-2015 in Japan).

RESULTS

Among 275 strains out of a total 1716 isolates, 23 (8.3%) were MBL-positive exhibiting resistant to meropenem (MEPM), imipenem, ceftazidime, cefepime, ciprofloxacin and levofloxacin without exception and the MIC of MEPM appeared over 128 μg/mL. Their MBL subtype analysis revealed that 16, 2, and 2 isolates were IMP-1, IMP-7 and VIM-2 positive, respectively, and one isolate each expressed either IMP-10, IMP-34 or IMP-41.

CONCLUSIONS

This study revealed that all the MBL-positive CRBP-r isolates were highly resistant to carbapenems dominating IMP-1 production.

Molecular analysis of the integrons of metallo-β-lactamase-producing Pseudomonas aeruginosa isolates collected by nationwide surveillance programs across Japan

Background

We investigate the evolving molecular epidemiology of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates collected in a 100 institution, nationwide surveillance study in Japan from 2004 to 2006.

Results

MBL-producers were detected in 23/996 isolates (2.3%) in 2004 and 21/992 (2.1%) in 2006. Antimicrobial resistance (specifically, carbapenem resistance) rates between two periods did not differ significantly. MBL-producers were more prevalent in urinary tract isolates. bla_IMP-1 group was the most predominant (38 isolates, 80%), followed by 3 bla_IMP-7, 2 bla_IMP-11 group, and 1 bla_VIM-1. All MBL genes were identified in 16 different class 1 integrons, most of which were novel to INTEGRALL database. A total of 17 isolates of sequence type (ST) 235, a recognized worldwide drug-resistant lineage, were distributed in 5 geographic regions across Japan. ST235 isolates included a sublineage associated with In113-like integron. ST357 was identified in 14 isolates, 9 of which harboring a sole bla_IMP-1 gene cassette (In994) were recovered from Chugoku region in 2004. ST357 isolates with bla_IMP-11 group or ST235 with bla_IMP-7 emerged in 2006. We also report for the first time the presence of novel fosI gene cassette in strains other than Mycobacterium spp.

Conclusions

Our data give an important “snapshot” of the molecular characteristics and dynamics of MBL-producing lineages in P. aeruginosa in Japan. The significant association of specific genotypes and integrons implies that dissemination and transmission of the preexisting resistant lineage, rather than horizontal gene transfer in situ, might largely explain their endemicity.

Molecular Characterization of Imipenem-ResistantPseudomonas aeruginosain Hiroshima, Japan

Pseudomonas aeruginosa showing resistance to imipenem were found in 100 of 1,058 strains (9.5%) from six hospitals (a-f) in Hiroshima City, Japan. Of the 100 strains, 14 (14%) were double disk synergy test positive using sodium mercaptoacetic acid disks, and 18 (18%) were bla(IMP-1) or bla(VIM-2) allele positive by polymerase chain reaction (PCR). Among 100 imipenem-resistant strains, 32 were categorized into multi-drug resistant strains, in which 13 were positive for the metallo-beta-lactamase gene. Fifty-one strains (51%) among the 100 imipenem-resistant strains had elevated RND efflux pump activity against levofloxacin. But only 6 of 51 strains were classified as multi-drug resistant strains. The pulsed field gel electrophoresis analysis of the Spe I-digested DNA from the 100 isolates suggested not only clonal spread but spread of heterogeneous clones started to contribute to the prevalence of metallo-beta-lactamase producing P. aeruginosa strains in Japanese hospitals.

Molecular characterization of carbapenem-non-susceptible Acinetobacter spp. in Japan: predominance of multidrug-resistant Acinetobacter baumannii clonal complex 92 and IMP-type metallo-β-lactamase-producing non-baumannii Acinetobacter species

We conducted an epidemiological study concerning carbapenem-non-susceptible clinical isolates of Acinetobacter spp. in Japan by molecular procedures including carbapenemase gene identification and amplified ribosomal DNA restriction analysis. Among 598 clinically isolated Acinetobacter spp. in 2007, 27 (4.5%) were non-susceptible to carbapenems. Most carbapenem-non-susceptible Acinetobacter baumannii (13/14) belonged to clonal complex (CC) 92, harbored bla (OXA-51-like) genes, including novel bla (OXA-206), downstream of ISAba1, and were recovered mainly from the Kanto region. Carbapenem-non-susceptible A. baumannii CC92 isolates were further divided by pulsed-field gel electrophoresis into two groups, one of which was characterized by the presence of bla (OXA-23). One A. baumannii CC276 isolate carried bla (IMP-1) and bla (OXA-58). Almost all non-baumannii Acinetobacter isolates (12/13), including Acinetobacter pittii (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU), produced IMP-type metallo-β-lactamases, and were recovered from various regions in Japan. This is the first report describing the nationwide molecular epidemiology of carbapenem-non-susceptible Acinetobacter spp. with genomic species-level identification in Japan.

Metallo-β-lactamase and genetic diversity of Pseudomonas aeruginosa in intensive care units in Campo Grande, MS, Brazil

Infection by Pseudomonas aeruginosa has spread worldwide, with limited options for treatment. The purpose of this study was to investigate metallo-β-lactamase-producing P. aeruginosa strains and compare their genetic profile using samples collected from patients in intensive care units. Forty P. aeruginosa strains were isolated from two public hospitals in Campo Grande, Mato Grosso do Sul State, from January 1st, 2007 to June 31st, 2008. Profiles of antimicrobial susceptibility were determined using the agar diffusion method. Metallo-β-lactamase was investigated using the double-disk diffusion test and PCR. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE). Respiratory and urinary tracts were the most common isolation sites. Of the 40 samples tested, 72.5% (29/40) were resistant to ceftazidime and 92.5% (37/40) to imipenem, whereas 65% (26/40) were resistant to both antimicrobials. Fifteen pan-resistant samples were found. Five percent (2/40) of samples were positive for metallo-β-lactamase on the phenotype test. No metallo-β-lactamase subtype was detected by PCR. Macrorestriction analysis revealed 14 distinct genetic patterns. Based on the superior accuracy of PCR, it can be inferred that P. aeruginosa isolates from the investigated hospitals have alternative mechanisms of carbapenem resistance. The results also suggest clonal spread of P. aeruginosa between the studied hospitals.

Genotypes and infection sites in an outbreak of multidrug-resistant Pseudomonas aeruginosa

An outbreak of multidrug-resistant (MDR) Pseudomonas aeruginosa occurred in an acute care hospital in Japan, which lasted for more than three years. During January 2006 to June 2009, 59 hospitalised patients with MDR P. aeruginosa were mainly detected by urine culture in the first half, whereas isolation from respiratory tract samples became dominant in the latter half of the outbreak. Non-duplicate MDR P. aeruginosa isolates were available from 51 patients and all isolates were positive for bla(VIM-2). Pulsed-field gel electrophoresis (PFGE) analysis categorised the isolates into three major clusters; types A, B and C with eight, 19 and 21 isolates, respectively. The outbreak started with patients harbouring PFGE type A strains, followed by type B, and type C strains. Multivariate analysis demonstrated that patients with PFGE type C strains were more likely to be detected by respiratory tract samples (odds ratio: 11.87; 95% confidence interval: 1.21-116.86). Improved aseptic urethral catheter care controlled PFGE type A and type B strains and improvement in respiratory care procedures finally contained the transmission of PFGE type C strains.

VIM and IMP metallo-β-lactamases and other extended-spectrum β-lactamases in Escherichia coli and Klebsiella pneumoniae from environmental samples in a Tunisian hospital

An extremely drug-resistant Enterobacteriaceae species emerged in Kasserine Hospital, Tunisia between 2009 and 2010 causing a local outbreak. We aimed to characterize extended-spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL)-producing Enterobacteriaceae from the hospital environment. Swabs were collected from ten different wards from Kasserine Hospital, Tunisia. A total of 46 isolates were cultured onto MacConkey agar supplemented with ceftazidime to select for ESBL-producing Enterobacteriaceae. Identification and susceptibility patterns were performed using Phoenix-automated phenotypic identification criteria. Extended spectrum β-lactamases (ESBLs) were detected using cefepime ESBL E-test. Colony blotting was first used to detect the occurrence of bla(SHV) , bla(CTX-M) , bla(CMY) , bla(IMP) , and bla(VIM) genes. PCR was used to amplify these genes, and the amplicons were sequenced and analyzed. Total DNA was digested with XbaI, and PFGE was used to type the major isolates that produced IMP-1. Among the 46 isolates, 63% were Klebsiella pneumoniae, 13% were Escherichia coli, 8.7% were Proteus mirabilis, 6% were Enterobacter cloaceae, 4.3% were Providencia rettgeri, 2.5% were Serratia marcescens, and 2.5% were Pantoea agglomerans. PCR amplification and DNA sequencing showed that hospital environment isolates produced SHV-125, CTX-M-15, CMY-2 ESBLs, and IMP-1 and VIM-2 MBLs. PFGE typing showed the emergence of IMP-1 MBL-producing K. pneumoniae isolates that were not clonal. In this study, we report the first characterization of IMP-1 and VIM-2 MBL-producing K. pneumoniae and E. coli isolates collected from Kasserine Hospital, Tunisia.

In vitro potentiation of carbapenems with ME1071, a novel metallo-beta-lactamase inhibitor, against metallo-beta-lactamase- producing Pseudomonas aeruginosa clinical isolates

ME1071, a maleic acid derivative, is a novel specific inhibitor for metallo-beta-lactamases (MBL). In this study, the potentiation of ME1071 in combination with several beta-lactams was evaluated using MBL-producing Pseudomonas aeruginosa isolates. The rates of susceptibility of MBL producers to carbapenems (imipenem, biapenem, and doripenem) and ceftazidime were increased by 8 to 27% in the presence of 32 microg/ml of ME1071. The corresponding resistance rates were decreased by 13 to 46%, respectively. On the other hand, ME1071 showed weaker or no potentiation with non-MBL producers. The K(i) value of ME1071 for IMP-1 was 0.4 microM, significantly lower than the K(m) values of carbapenems for the IMP-1 enzyme. On the other hand, the K(i) value of ME1071 for VIM-2 was 120 microM, higher than the K(m) values of carbapenems for the VIM-2 enzyme. Results of this study indicate that ME1071 can potentiate the activity of ceftazidime and carbapenems against MBL-producing strains of P. aeruginosa.

Bench-to-bedside review: The role of beta-lactamases in antibiotic-resistant Gram-negative infections

Multidrug resistance has been increasing among Gram-negative bacteria and is strongly associated with the production of both chromosomal- and plasmid-encoded β-lactamases, whose number now exceeds 890. Many of the newer enzymes exhibit broad-spectrum hydrolytic activity against most classes of β-lactams. The most important plasmid-encoded β-lactamases include (a) AmpC cephalosporinases produced in high quantities, (b) the expanding families of extended-spectrum β-lactamases such as the CTX-M enzymes that can hydrolyze the advanced-spectrum cephalosporins and monobactams, and (c) carbapenemases from multiple molecular classes that are responsible for resistance to almost all β-lactams, including the carbapenems. Important plasmid-encoded carbapenemases include (a) the KPC β-lactamases originating in Klebsiella pneumoniae isolates and now appearing worldwide in pan-resistant Gram-negative pathogens and (b) metallo-β-lactamases that are produced in organisms with other deleterious β-lactamases, causing resistance to all β-lactams except aztreonam. β-Lactamase genes encoding these enzymes are often carried on plasmids that bear additional resistance determinants for other antibiotic classes. As a result, some infections caused by Gram-negative pathogens can now be treated with only a limited number, if any, antibiotics. Because multidrug resistance in Gram-negative bacteria is observed in both nosocomial and community isolates, eradication of these resistant strains is becoming more difficult.

Dissemination of multidrug-resistant Acinetobacter baumannii genotypes carrying bla(OXA-23) collected from hospitals in Rio de Janeiro, Brazil

The present study reports the dissemination of multidrug-resistant (MDR) OXA-23-producing Acinetobacter baumannii clones throughout hospitals in Rio de Janeiro, Brazil. A total of 110 imipenem-resistant A. baumannii isolates were obtained from January 2006 to September 2007 in eight hospitals. The modified Hodge test was performed to screen for carbapenemase production. Polymerase chain reaction (PCR) and DNA sequencing were performed for the detection of bla(IMP), bla(VIM), bla(OXA-23-like), bla(OXA-24-like), bla(OXA-58) and the class 1 integron. Isolates were typed by pulsed-field gel electrophoresis (PFGE) following digestion with ApaI. All the isolates were MDR and 96 (87.3%) produced the carbapenemase OXA-23. No isolates produced OXA-24, OXA-58 or the metallo-beta-lactamases IMP and VIM. The class 1 integron was absent in all isolates. The A. baumannii isolates were separated into five genotypes, with the highest prevalence of genotype A (71.8%) followed by genotype B (22.7%). Genotype A was present in seven hospitals, whilst genotype B had spread in five hospitals. The OXA-23-producing isolates belonged to all genotypes. The presence of MDR OXA-23-producing A. baumannii in different hospitals in Rio de Janeiro emphasises the need to control the use of carbapenems and to prevent the spread of these organisms in Rio de Janeiro.

First countrywide survey of acquired metallo-beta-lactamases in gram-negative pathogens in Italy

Metallo-beta-lactamases (MBLs) can confer resistance to most beta-lactams, including carbapenems. Their emergence in gram-negative pathogens is a matter of major concern. Italy was the first European country to report the presence of acquired MBLs in gram-negative pathogens and is one of the countries where MBL producers have been detected repeatedly. Here, we present the results of the first Italian nationwide survey of acquired MBLs in gram-negative pathogens. Of 14,812 consecutive nonreplicate clinical isolates (12,245 Enterobacteriaceae isolates and 2,567 gram-negative nonfermenters) screened for reduced carbapenem susceptibility during a 4-month period (September to December 2004), 30 isolates (28 Pseudomonas aeruginosa isolates, 1 Pseudomonas putida isolate, and 1 Enterobacter cloacae isolate) carried acquired MBL determinants. MBL producers were detected in 10 of 12 cities, with a predominance of VIM-type enzymes over IMP-type enzymes (4:1). Although having an overall low prevalence (1.3%) and significant geographical differences, MBL-producing P. aeruginosa strains appeared to be widespread in Italy, with a notable diversity of clones, enzymes, and integrons carrying MBL gene cassettes.

Potency of IMP-10 metallo-beta-lactamase in hydrolysing various antipseudomonal beta-lactams

Limited beta-lactams show antipseudomonal activity. The rapid spread of IMP-type metallo-beta-lactamases (MBLs), which have a broad spectrum of substrates and a poor susceptibility to clinically available inhibitors, further restricts beta-lactam use. In the present study, we evaluated the potency of IMP-10 MBL in hydrolysing antipseudomonal beta-lactams currently available in the clinic. Crude IMP-10 MBL was prepared from two clinical isolates of Pseudomonas aeruginosa harbouring the bla(IMP-10) gene. The sensitivity of beta-lactams to hydrolysis by IMP-10 MBL was determined by comparing the MICs of 14 antipseudomonal beta-lactams against a susceptible strain of P. aeruginosa in the presence and absence of IMP-10 MBL. Carbapenems (imipenem, meropenem and panipenem) and extended-spectrum cephems (ceftazidime, cefoperazone, cefsulodin and cefepime) were sensitive to the hydrolysing activity of IMP-10 MBL. By comparison, the fourth-generation cephem (cefpirome), the extended-spectrum penicillins (carbenicillin, ticarcillin, piperacillin and mezlocillin) and monobactams (aztreonam and carumonam) were relatively resistant to IMP-10 MBL. The sensitivity profile of antipseudomonal beta-lactams to IMP-10 MBL generated in the present study provides a valuable reference for antibiotic selection by medical professionals.

Molecular epidemiology of carbapenem-resistant Pseudomonas aeruginosa carrying metallo-β-lactamase genes in Taiwan

Seventy-two isolates of carbapenem-resistant Pseudomonas aeruginosa (CRPA) collected through the Taiwan Surveillance of Antimicrobial Resistance (TSAR) program in 2000 and 2002 were studied for carriage of metallo-beta-lactamase (MBL), integrase genes, and integrons. Epidemiologic relatedness was determined using pulsed-field gel electrophoresis. The prevalence of the MBL genes among CRPA was 36.0% (9 of 25) in TSAR II and 17.0% (8/47) in TSAR III, with prevalence in surveyed hospitals being 19.1% (4/21, TSAR II) and 23.1% (6 of 26, TSAR III). The bla(VIM-3) was detected in 15 of the 17 MBL-positive isolates; the remainder possessed bla(VIM-2). The bla(IMP) was not evident. Class 1 integron was detected in all MBL-positive isolates; amplicon DNA sequences containing the bla(VIM-3) regions were all identical. All MBL-positive isolates remained susceptible to colistin. Molecular typing revealed a predominant strain that comprised 14 of the isolates among the various surveyed hospitals.

Carbapenemases: the versatile beta-lactamases

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Nosocomial outbreak of genetically related IMP-1 β-lactamase-producing Klebsiella pneumoniae in a general hospital in Japan

Gram-negative bacteria with acquired metallo-beta-lactamase (MBL) resistance are being increasingly described worldwide. Here we report the first case of an outbreak by a cluster of genetically related strains of Klebsiella pneumoniae producing the IMP-1 MBL. Six isolates of K. pneumoniae with a ceftazidime minimum inhibitory concentration >/=64 microg/mL were collected between February 2003 and June 2004 in Hanyu General Hospital, Saitama, Japan. These isolates were analysed to establish the mechanism of resistance. The zone of inhibition of these isolates using ceftazidime or imipenem disks on Mueller-Hinton agar containing dipicolinic acid was much larger than on Mueller-Hinton agar without dipicolinic acid. Polymerase chain reaction and DNA sequencing confirmed that the isolates contained bla(IMP-1) as well as intI1 as a class I integrase gene. Pulsed-field gel electrophoresis was performed, showing that five of the six isolates were related. This outbreak was controlled by restrained and careful use of antibiotics as well as strict hygiene practices.

Outbreaks of multidrug-resistant Pseudomonas aeruginosa in community hospitals in Japan

We previously reported an outbreak in a neurosurgery ward of catheter-associated urinary tract infection with multidrug-resistant (MDR) Pseudomonas aeruginosa strain IMCJ2.S1, carrying the 6'-N-aminoglycoside acetyltransferase gene [aac(6')-Iae]. For further epidemiologic studies, 214 clinical isolates of MDR P. aeruginosa showing resistance to imipenem (MIC >or= 16 microg/ml), amikacin (MIC >or= 64 microg/ml), and ciprofloxacin (MIC >or= 4 microg/ml) were collected from 13 hospitals in the same prefecture in Japan. We also collected 70 clinical isolates of P. aeruginosa that were sensitive to one or more of these antibiotics and compared their characteristics with those of the MDR P. aeruginosa isolates. Of the 214 MDR P. aeruginosa isolates, 212 (99%) were serotype O11. We developed a loop-mediated isothermal amplification (LAMP) assay and a slide agglutination test for detection of the aac(6')-Iae gene and the AAC(6')-Iae protein, respectively. Of the 212 MDR P. aeruginosa isolates, 212 (100%) and 207 (98%) were positive in the LAMP assay and in the agglutination test, respectively. Mutations of gyrA and parC genes resulting in amino acid substitutions were detected in 213 of the 214 MDR P. aeruginosa isolates (99%). Of the 214 MDR P. aeruginosa isolates, 212 showed pulsed-field gel electrophoresis patterns with >or=70% similarity to that of IMCJ2.S1 and 83 showed a pattern identical to that of IMCJ2.S1, indicating that clonal expansion of MDR P. aeruginosa occurred in community hospitals in this area. The methods developed in this study to detect aac(6')-Iae were rapid and effective in diagnosing infections caused by various MDR P. aeruginosa clones.

Molecular epidemiology of metallo-beta-lactamase-producing Pseudomonas aeruginosa in the Calgary Health Region: emergence of VIM-2-producing isolates

A study was designed to describe the molecular epidemiology of carbapenem-resistant (CR) Pseudomonas aeruginosa in a large well-defined geographical region with a centralized laboratory system serving one pediatric and three large adult hospitals (acute care centers I, II, and III). Molecular characterization was done using PCR with sequencing of the integron-associated gene cassettes. Pulsed-field gel electrophoresis (PFGE) using a modified combined Stenotrophomas maltophilia and Streptococcus pneumoniae protocol with SpeI was performed on CR P. aeruginosa strains isolated in the Calgary Health Region during 2002-2006. The majority (96%) of metallo-beta-lactamase (MBL)-producing isolates produced VIM-2 with gene cassettes aacC1 and aacA4, while 4% produced IMP-7 with gene cassettes aacC4 and aacC1. Eighty-six percent of VIM-2 producers belonged to a cluster (MBLV) that was responsible for nosocomial outbreaks during 2003 (intensive care unit) and 2004 (bone marrow transplant unit) at acute care center I. Environmental isolates from these units also belonged to MBLV. The majority of strains from cluster MBLVR (related to MBLV) were present in acute care center III. Isolates producing IMP-7 belonged to a different cluster (MBLI) and were related to strains described during the 1990 s. PFGE of the MBL-negative CR strains showed that 37% belonged to a closely related cluster, NMBL, whose members were predominantly isolated from acute care center II. Our findings suggest that CR and dissemination of MBL clusters among P. aeruginosa populations in large geographic healthcare regions are dynamic processes that require continuous molecular surveillance.

Integrons containing the VIM-2 metallo-beta-lactamase gene among imipenem-resistant Pseudomonas aeruginosa strains from different Chinese hospitals

A total of 140 nonrepetitive strains of imipenem-resistant Pseudomonas aeruginosa were isolated from five different Chinese hospitals. Fourteen isolates were confirmed to contain the VIM-2 metallo-beta-lactamase gene. Twelve isolates harbored two kinds of class 1 integron, containing both VIM-2- and aminoglycoside-resistant genes.

Contemporary activity of meropenem and comparator broad-spectrum agents: MYSTIC program report from the United States component (2005)

The Meropenem Yearly Susceptibility Test Information Collection Program is a 9-year-old antimicrobial resistance surveillance network of more than 100 medical centers worldwide, including 15 sites in the United States (US) that monitors the susceptibility of Gram-negative and Gram-positive bacterial pathogens especially to carbapenems. In 2005, the antimicrobial activity of 11 broad-spectrum agents was assessed against 2910 bacterial isolates (2493 Gram-negative and 417 staphylococci) submitted from the US medical centers to a reference laboratory using Clinical and Laboratory Standards Institute susceptibility testing methods and interpretative criteria. Meropenem continued to demonstrate 1) high potency with MIC(90) values 4- to 16-fold lower than imipenem against the Enterobacteriaceae, 2) equal activity against Pseudomonas aeruginosa, 3) 2-fold less activity compared with imipenem against Acinetobacter spp., and 4) 4- to 8-fold less activity compared with imipenem against the oxacillin-susceptible staphylococci. The wide spectrum of activity for carbapenems against Enterobacteriaceae (1657 strains) was confirmed by the overall rank order by percentage susceptibility at breakpoint criteria: imipenem (98.9%) > meropenem (98.7%) > cefepime (97.6%) > piperacillin/tazobactam (92.0%) > ceftriaxone (91.2%) > aztreonam (90.6%) > gentamicin = tobramycin (90.5%) > ceftazidime (90.4%) > levofloxacin (84.9%) > ciprofloxacin (83.9%). Against Acinetobacter spp. isolates, only tobramycin (92.0% susceptible) and carbapenems (92.0-85.6%) exhibited acceptable levels of activity. A continued increase in the resistance rate for both ciprofloxacin and levofloxacin was observed with highest rates found among indole-positive Proteae species (36.5-33.3%) and Escherichia coli (21.6-20.4%) isolates, some documented by molecular typing methods as clonally related. Ongoing surveillance of meropenem and other broad-spectrum antimicrobial agents appears warranted to monitor the potency and spectrum of activity against indicated Gram-negative and-positive pathogens causing serious infections in the hospital setting, and to detect the emergence of new or novel resistance mechanisms that could compromise clinical utility (serine and metallo-carbapenemases).

Evaluation of antimicrobial activity of beta-lactam antibiotics by Etest against clinical isolates from 100 medical centers in Japan (2004)

This antimicrobial resistance surveillance study was performed in 100 medical centers. The susceptibility of 9347 strains including Escherichia coli (997 strains), Klebsiella spp. (997 strains), Enterobacter spp. (988 strains), Citrobacter spp. (834 strains), indole-positive Proteae spp. (855 strains), Serratia spp. (925 strains), Acinetobacter spp. (902 strains), Pseudomonas aeruginosa (996 strains), oxacillin-susceptible Staphylococcus aureus (992 strains), and coagulase-negative staphylococci (861 strains) to 7 beta-lactam antibiotics, cefepime, cefpirome, ceftazidime, cefoperazone/sulbactam, imipenem and piperacillin (for gram negatives), or oxacillin (for gram positives) was tested. No strain resistant to these beta-lactams except for ceftazidime was found in oxacillin-susceptible S. aureus and coagulase-negative staphylococci. E. coli (16.5%) clinical isolates were resistant to piperacillin, whereas 1.5% or less (cefpirome = 1.5%) was resistant to other beta-lactams. Klebsiella spp. strains were more susceptible to imipenem (99.7%), cefepime (98.4%), and cefpirome (97.3%). Isolates of Enterobacter spp., Citrobacter spp., indole-positive Proteae, and Serratia spp. were susceptible to imipenem, cefepime, and cefpirome, as well. Acinetobacter spp. strains were most susceptible to cefoperazone/sulbactam (0.8% resistance), imipenem (3.2%), ceftazidime (6.0%), and cefepime (7.0%) than other beta-lactam antibiotics tested. Isolates of P. aeruginosa were more susceptible to ceftazidime (9.9% resistance), cefoperazone/sulbactam (14.9%), and cefepime (11.2%) than piperacillin (15.5%), cefpirome (19.1%), and imipenem (19.3%). The percentage of imipenem-resistant P. aeruginosa is around 20% in clinical isolates in Japan.

Metallo-beta-lactamase IMP-1 in Providencia rettgeri from two different hospitals in Japan

In 2002, 495 indole-positive proteae strains were isolated from patients at 60 hospitals in Japan. Nine indole-positive proteae strains had reduced susceptibility to imipenem (MIC > or = 8 microg ml(-1)) and were identified as Providencia rettgeri by BD Phoenix. Eight of the nine Prov. rettgeri isolates were confirmed as metallo-beta-lactamase producers by the double-disc synergy test. All the metallo-beta-lactamases were classified as IMP-1 by PCR and DNA sequence analysis. These bla(IMP-1) genes were encoded in the integron structure on conjugative plasmids. These plasmids could transfer from Prov. rettgeri clinical isolates to Escherichia coli ML4903 at a frequency between 1.5 x 10(-5) and 5.5 x 10(-7). The eight bla(IMP)-positive strains were isolated from two hospitals, and showed two different PFGE patterns, two different integron structures and two different incompatibility groups, which corresponded to the two hospitals. These results strongly suggest the possibility of nosocomial infections by bla(IMP-1)-producing Prov. rettgeri isolates.

Evaluation of dipicolinic acid for detection of IMP- or VIM- type metallo-β-lactamase–producing Pseudomonas aeruginosa clinical isolates

We evaluated dipicolinic acid (DPA) as a chelating agent for detection of IMP- or VIM-type metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa clinical isolates. Using the broth microdilution testing in the presence or absence of DPA, MBL producers exhibited 100%, 92%, or 100% of >or=8 times (media, 32 times) reduction of MICs in presence of DPA for ceftazidime, imipenem, or meropenem, respectively. In disk diffusion testing, expansion of growth inhibitory zone of these clinical isolates was clearly observed. Thus, DPA could be useful in the detection for MBL-producing P. aeruginosa clinical isolates.

Evaluation of antimicrobial activity of beta-lactam antibiotics using Etest against clinical isolates from 60 medical centres in Japan

An antimicrobial resistance surveillance study was carried out in 60 medical centres across Japan. Resistance to piperacillin was 10.8% in clinical isolates of Escherichia coli, while 1.3% or fewer isolates were resistant to other beta-lactams. Klebsiella spp. were more susceptible to imipenem, cefepime and cefpirome. Isolates of Enterobacter spp., Citrobacter spp., indole-positive Proteus and Serratia spp. were susceptible to imipenem, cefepime and cefpirome, while Acinetobacter spp. were most susceptible to cefoperazone/sulbactam, imipenem, ceftazidime (5.8% resistance) and cefepime (7.6%). Isolates of Pseudomonas aeruginosa were more susceptible to ceftazidime (12.3% resistance), cefoperazone/sulbactam (12.5%) and cefepime (12.6%) than to piperacillin (15.0%), cefpirome (22.6%) and imipenem (30.8%). The percentage of Japanese imipenem resistant P. aeruginosa clinical isolates was around 30%.