Clinical and bacteriological characteristics of IMP-type metallo-beta-lactamase-producing Pseudomonas aeruginosa

Dissemination of the metallo-beta-lactamase gene blaIMP-4 among gram-negative pathogens in a clinical setting in Australia

BACKGROUND

The clinical utility of carbapenems is under threat because of the emergence of acquired metallo-beta-lactamase (MBL) genes. We describe the first outbreak in Australia of infection and/or colonization with gram-negative pathogens carrying the MBL gene blaIMP-4.

METHODS

MBL-producing organisms were identified using susceptibility data in conjunction with MBL screening methods. PCR and sequence analysis were performed to characterize the resistance gene and identify the presence of integrons. DNA profiles were determined by ribotyping. Clinical and epidemiological data were prospectively collected from January-July 2004.

RESULTS

A total of 19 isolates were recovered from 16 patients: Serratia marcescens (10 isolates), Klebsiella pneumoniae (4 isolates), Pseudomonas aeruginosa (3 isolates), Escherichia coli (1 isolate), and Enterobacter cloacae (1 isolate). Isolates were resistant to most beta-lactams except aztreonam, and variable resistance to carbapenems was observed (MIC range, 2 to >8 mg/L). PCR and sequence analysis identified the blaIMP-4 gene and a class 1 integrase (IntI1) in all isolates. Of the 16 patients, 12 (75%) had infection; 5 had septicemia, 5 had ventilator-associated pneumonia, 1 had a urinary tract infection, and 1 had a superficial central venous line infection. Six (38%) of the 16 patients died, and 5 of those 6 (31% of the group of 16) had clinical infection with an MBL-producing organism. All except 2 patients had spatio-temporal epidemiological links in the intensive care unit. All K. pneumoniae isolates were of different ribogroups, whereas the S. marcescens and P. aeruginosa isolates were predominately of the same ribogroup.

CONCLUSIONS

MBL-producing gram-negative organisms have now emerged in Australia. The resistance gene, blaIMP-4, appears highly mobile; this outbreak involved 5 different gram-negative genera from patients with close epidemiological links.

Detection of Pseudomonas aeruginosa producing metallo-beta-lactamases in a large centralized laboratory

Metallo-beta-lactamases (MBLs) have been increasingly recognized from clinical isolates worldwide, but the laboratory detection of these strains is not well defined. We report a study that developed an EDTA disk screen test and a molecular diagnostic assay for the detection of MBL-producing Pseudomonas aeruginosa. Using NCCLS disk methodology, inhibition zone diameters were determined in tests with imipenem (IPM) and meropenem (MEM) disks alone and in combination with 930 microg of EDTA. This test was compared with the MBL Etest. The duplex PCR assay showed 100% sensitivity and specificity for detecting MBL-producing control strains. Of the 241 clinical strains of IPM-nonsusceptible P. aeruginosa from the Calgary Health Region isolated from 2002 to 2004, 110/241 (46%) were MBL positive using phenotypic methods while 107/241 (45%) were PCR positive for MBL genes: 103/241 (43%) for bla(VIM) and 4/241 (2%) for bla(IMP). The EDTA disk screen test using MEM showed 100% sensitivity and 97% specificity for detecting MBLs in control and clinical strains. The EDTA disk screen test is simple to perform and to interpret and can easily be introduced into the workflow of a clinical laboratory. We recommend that all IPM-nonsusceptible P. aeruginosa isolates be routinely screened for MBL production using the EDTA disk screen test and that PCR confirmation be performed at a regional laboratory.

Pan-drug-resistant Pseudomonas aeruginosa causing nosocomial infection at a university hospital in Taiwan

This study evaluated the clinical and microbiological characteristics of 16 patients who were colonised or infected with 26 isolates of pan-drug-resistant Pseudomonas aeruginosa (PDRPA; intermediately-resistant or resistant to all cephalosporins, piperacillin-tazobactam, aztreonam, carbapenems, ciprofloxacin and aminoglycosides) in a university hospital during 1999-2002. All the isolates had colistin MICs < or = 4 mg/L, 19 (73%) isolates had bla(VIM-3), and 25 (96%) isolates had class I integrons (intI). Time-kill studies for two PDRPA blood isolates demonstrated synergism for cefepime-amikacin after 24 h. Pulsed-field gel electrophoresis analysis of the isolates revealed a polyclonal nature (12 pulsotypes), although clonal dissemination of PDRPA isolates among these patients was also present.

Evaluation of Etest MBL for detection of blaIMP-1 and blaVIM-2 allele-positive clinical isolates of Pseudomonas spp. and Acinetobacter spp

The Etest MBL (AB BIODISK, Solna, Sweden) correctly differentiated all 57 isolates of Acinetobacter spp. and Pseudomonas aeruginosa with the bla(IMP-1) allele and 135 of 137 (98.5%) Acinetobacter spp. and Pseudomonas spp. isolates with the bla(VIM-2) allele. The Etest MBL was reliable for detecting the IMP-1- and VIM-2-producing Pseudomonas and Acinetobacter isolates.

Outbreak of carbapenem-resistant Pseudomonas aeruginosa producing VIM-8, a novel metallo-beta-lactamase, in a tertiary care center in Cali, Colombia

The prevalence of imipenem resistance among Pseudomonas aeruginosa isolates at a 195-bed tertiary care medical center in Cali, Colombia, rose from 2% in 1996 to 28% in 1997 and to over 40% in 2003. Many isolates showed high-level multiresistance, and phenotypic characterization suggested the spread of a predominant strain with minor variants. Sixty-six resistant isolates collected between February 1999 and July 2003 from hospitalized patients (n = 54) and environmental samples (n = 12) were subjected to a fuller analysis. Genetic fingerprints were compared by pulsed-field gel electrophoresis (PFGE) of SpeI-digested genomic DNA, and bla(IMP) and bla(VIM) genes were sought by PCR. PFGE and serotyping indicated that 52 of the 66 isolates belonged to a single strain, with 82% similarity; the PFGE pattern for this organism was designated pattern A. Two further pairs of isolates represented single strains; the remaining nine isolates were unique, and in the case of one isolate, no satisfactory PFGE profile could be obtained. The pattern A isolates were mostly of serotype O12 and were highly resistant to imipenem (MICs, 32 to >256 microg/ml), with this resistance decreased eightfold or more in the presence of EDTA. They yielded amplicons with bla(VIM)-specific primers, and sequencing of DNA from a representative isolate revealed bla(VIM-8), a novel allele with three polymorphisms compared with the sequence of bla(VIM-2). Two of these nucleotide changes were silent, but the third determined a Thr139Ala substitution. Only 4 of 13 resistant isolates (2 clinical isolates and 2 environmental isolates) assigned to other PFGE types carried bla(VIM) alleles, whereas the others were less multiresistant and mostly had lower levels of imipenem resistance (MICs, < or =32 microg/ml) which was not significantly reduced by EDTA. No bla(IMP) alleles were detected. During 2003, when the environmental study was undertaken, serotype O12 isolates with bla(VIM) were recovered from sinks and stethoscopes in the most-affected units, although not from the hands of staff; the problem declined once these reservoirs were disinfected and hygienic precautions were reinforced.

Newer carbapenems for urinary tract infections

Four carbapenems have been available clinically in Japan. These are imipenem/cilastatin (IMIP/CS) and panipenem/ betamipron (PANI/BP) of the older compounds and newer carbapenems such as biapem (BIAP) and meropenem (MERO). The latter compounds are relatively stable to dehydropeptidase-1 (DHP-1) and have been reported to have higher antimicrobial activities compared to the earlier carbapenems. The antimicrobial activity of these four carbapenems against fresh urinary isolates showed high activities against Enterobacteriacae such as Serratia marcescens, Enterobacter cloacae, Citrobacter freundii and Escherichia coli containing the class C-beta-lactamase- and extended spectrum beta-lactamase (ESBL)-producing strains compared to piperacillin (PIPC) and ceftazidime (CTAZ). Against Pseudomonas aeruginosa, the carbapenems, with the exception of panipenem showed strong antimicrobial activities compared to PIPC and CTAZ. High activities were also seen against Enterococcus faecalis, Staphylococcus aureus and Staphylococcus epidermidis, but methicillin-resistant strains were not affected. The first generation carbapenems showed better activity against E. faecalis than newer carbapenems. All four carbapenems were similar in clinical effectiveness in double blind trials for complicated urinary tract infections (UTIs). However, PANI/BP is less effective in UTIs caused by P. aeruginosa than IMIP/CS. MERO showed better eradication rate of P. aeruginosa than IMIP/CS. Retrospective analysis of treated cases using carbapenems showed a rapid defervescence in the treatment of febrile complicated UTIs, which were mainly caused by mixed infection of Gram-negative and Gram-positive bacteria, especially those involving P. aeruginosa and E. faecalis.

Metallo-β-lactamase-producing Gram-negative bacilli in Korean Nationwide Surveillance of Antimicrobial Resistance group hospitals in 2003: Continued prevalence of VIM-producing pseudomonas spp. and increase of IMP-producing Acinetobacter spp

Metallo-beta-lactamase (MBL)-producing Pseudomonas spp. and Acinetobacter spp. were prevalent in Korean hospitals. In this study, the prevalence and presence of MBL-producing isolates among imipenem-nonsusceptible and imipenem-susceptible isolates, respectively, were screened. The genetic and phenotypic characteristics of MBL-producing isolates were determined. Among imipenem-nonsusceptible isolates, 52 (11.1%) of 467 Pseudomonas spp. were blaVIM-like allele-positive, and 33 (15.1%) of 218 Acinetobacter spp. were either blaVIM- or blaIMP-like allele-positive. One blaVIM-like allele-positive isolate of Acinetobacter spp. was detected among 84 imipenem-susceptible Acinetobacter isolates. The minimum inhibitory concentration for 90% of isolates of imipenem was higher (>128 microg/mL) for Pseudomonas spp. than Acinetobacter spp. (16 microg/mL), although both had blaVIM-like allele. The source of MBL-producing isolates was mostly the sputum and urine of patients in the intensive care unit. Pulsed-field gel electrophoresis analysis suggested the intra- and inter-hospital spread of MBL-producing strains at some hospitals. In conclusion, blaVIM-like allele-positive P. aeruginosa remained highly prevalent, and the proportion of blaIMP-like allele-positive Acinetobacter spp. has increased significantly in most Korean hospitals.

Evaluation of the contemporary occurrence rates of metallo-β-lactamases in multidrug-resistant Gram-negative bacilli in Japan: Report from the SENTRY Antimicrobial Surveillance Program (1998–2002)

Metallo-beta-lactamases (M beta L) were initially characterized in Japan, usually of the IMP-type, and found in Pseudomonas aeruginosa (PSA), Acinetobacter spp. (ACB), or Serratia marcescens (SM). The number of M beta L types has increased worldwide, but geographic dissemination within Japan has appeared limited. This study compares baseline levels of M beta L resistance from two 22-center studies (1996-1997) to the longitudinal sample (3 sites) of Japanese isolates from the SENTRY Antimicrobial Surveillance Program (1998-2002). All minimal inhibitory concentration results were determined by reference methods. A total of 26.8% PSA, 3.4% ACB, and 3.1% Enterobacteriaceae (enterobacters and SM) with resistance to monitored carbapenems (CARB) (minimal inhibitory concentration, > or =8 microg/mL) were screened for M beta L production by disk approximation tests (EDTA and 2-MPA inhibitors), CARB hydrolysis by enzyme extracts, and selected PCR primers for known M beta L types. All M beta L-positive strains (10) were sequenced to determine enzyme identification. Clonality in each center was determined by automated ribotyping and PFGE. The CARB susceptibility rates in PSA decreased (80.7% to 62.0%) over the monitored interval (1998-2002), but varied by medical center location. Among CARB-resistant isolates, 10.8% were attributed to M beta L strains (1.1% of all PSA tested). M beta L identification showed the following: five PSA (three IMP-1, two IMP-2), four SM (one IMP-1, two IMP-1 + OXA-1, and one IMP-11). Also a single ACB had an IMP-1. Eight of 10 M beta L isolations occurred between 2000 and 2002; four occurred in 2002. BRL42715, an AMP-C inhibitor, confirmed AMP-C-mediated resistance in 87.3% of PSA, and outer membrane protein changes were also discovered by membrane studies. Prior results (22 sites, 1997-1998) showed CARB resistance at 22.4-25.6% and 0.5-0.9% M beta Ls (IMP-1) overall; it was slightly elevated in this SENTRY Program sample. In conclusion, M beta L-producing strains from several species persist in Japan, but represent a distinct minority of all CARB-resistant strains (1998-2002). Although M beta L rates appear generally stable in Japan, continued surveillance for these mechanisms seems to be a prudent practice, because of the mobility of the genetic determinants and the emergence of novel enzyme types, especially among the Enterobacteriaceae.

Virulence of metallo-beta-lactamase-producing Pseudomonas aeruginosa in vitro and in vivo

We evaluated the virulence of Pseudomonas aeruginosa carrying bla(IMP), a metallo-beta-lactamase gene, and the efficacy of ceftazidime, imipenem-cilastatin, and ciprofloxacin in the endogenous bacteremia model. The presence of bla(IMP) did not practically change the virulence of the parent strain, and ciprofloxacin was effective against infection with P. aeruginosa carrying bla(IMP).