nonduplicate , imipenem - resistant isolates of 387 pseudomonas spp . and 267 acinetobacter spp . were collected from 2000 to 2001 from 28 hospitals in the korean nationwide surveillance of antimicrobial resistance group hospitals located in six cities or provinces .
the identification of the species and the imipenem susceptibility were confirmed at the coordinating laboratory by using conventional tests ( 11 ) or atb 32 gn system ( biomerieux , marcy - letoile , france ) and by using the disk diffusion test ( 12 ) , respectively .
mbl production was screened by using the hodge test and the imipenem - edta double disk synergy test ( 13 ) .
the blaimp-1 and blavim-2 alleles were detected by polymerase chain reaction ( pcr ) , and three of the positive isolates were confirmed by sequencing , as described previously ( 4 ) .
xbai - digested genomic dna of p. aeruginosa isolates was separated by pfge using the chef - dr - ii system ( bio - rad laboratories , hercules , ca ) ( 4 ) .
the pattern was analyzed visually and by using uviband and map software ( uvitec ltd .
, cambridge , uk ) . some of the pseudomonas and acinetobacter isolates collected were not fully resistant to imipenem but showed intermediate resistance when retested . among the isolates not susceptible to imipenem , 44 ( 11.4% ) of 387 pseudomonas spp .
( 42 p. aeruginosa and 2 p. putida ) and 38 ( 14.2% ) of 267 acinetobacter spp
. were considered mbl producers on the basis of positive results by the hodge test and imipenem - edta double disk synergy test ( table 1 ) .
mbl - producing pseudomonas spp . and acinetobacter spp . were detected in 11 ( 52.4% ) of 21 and 10 ( 41.7% ) of 24 hospitals that were located in four of five and five of six cities or provinces , respectively .
we detected the blavim allele by pcr from all 42 isolates of mbl - producing p. aeruginosa and 2 isolates of p. putida .
the blavim-2 and blaimp-1 alleles were detected in 27 ( 71.1% ) and 11 ( 28.9% ) of 38 acinetobacter isolates , respectively ( table 2 ) .
nucleotide sequencing for three representative pcr - positive isolates confirmed the presence of the blavim-2 gene in one isolate each of p. aeruginosa and acinetobacter spp . , and the blaimp-1 gene in one isolate of acinetobacter spp .
the mbl - producing strains were isolated mainly from intensive - care unit patients ( 31.7% ) and other inpatients ( 50.0% ) ; five ( 6.1% ) were from emergency service and other outpatients ( table 3 ) .
overall , mbl - producing isolates were mainly obtained from specimens of sputum ( 50.0% ) and urine ( 29.3% ) .
however , the proportion of mbl - producing isolates was relatively higher among urine isolates : 17.3% for pseudomonas spp .
we obtained one mbl - producing acinetobacter isolate from each of the following specimen types : blood , spinal fluid , pleural fluid , and venous catheter tip ( table 4 ) .
others included one acinetobacter isolate from specimens from blood , spinal fluid , pleural fluid , and a venous catheter tip .
the pfge of the xbai - digested genomic dna of 39 isolates of p. aeruginosa showed 22 patterns ( data not shown ) .
thirteen isolates ( 33.3% ) belonged to another identical pattern  six from one hospital , two from each of two hospitals , and one from each of three hospitals , which were located in a city and two provinces .
in this study , > 10% of all imipenem - nonsusceptible isolates of pseudomonas spp . and acinetobacter spp .
were attributable to mbl production ( table 1 ) , and these mbl - producing isolates were detected in 62.5% of the participating hospitals .
our finding indicates that mbl - producing p. aeruginosa is more prevalent in korea than in other countries ( 2 ) and that mbl - producing acinetobacter spp .
the percentage of hospitals with mbl - producing isolates might have been higher if a larger number of imipenem - nonsusceptible isolates had been collected for this study .
vim-2producing p. aeruginosa was isolated at almost the same time in europe ( 7 ) and korea ( 4 ) .
however , imp-1producing isolates were rare until 2000 in korea . only one and three imp-1-positive p. aeruginosa and acinetobacter spp .
, respectively , have been isolated at the reference laboratory ( 4 , unpub . data ) . in our study , 11 ( 28.9% ) of 38 mbl - positive isolates of acinetobacter spp .
this increase suggests the possible introduction of imp - producing strains of acinetobacter spp . from japan , where 28 isolates of blaimp-1-positive acinetobacter baumannii were reported in a hospital as early as 1994 to 1996 ( 14 ) .
rasmussen and bush ( 15 ) predicted that an increase of mbl - producing organisms was inevitable , given the more frequent use of carbapenems .
imipenem has been used for only 9 years in korea , but the imipenem - resistance rate of p. aeruginosa has rapidly risen from 6% in 1996 to 19% in 2001 .
a study by the korean nationwide surveillance of antimicrobial resistance group showed that the mean imipenem - resistance rates of p. aeruginosa in 1997 did not differ substantially depending on hospital size , ( i.e. , 17% in medium hospitals [ < 1,000 beds ] and 18% in large hospitals [ > 1,000 beds ] ) .
the mean resistance rates to imipenem were not lower than those to ceftazidime in 2000 , i.e. , 21% versus 18% in large hospitals and 20% versus 19% in medium hospitals ( data not shown ) .
the imipenem resistance rate of this organism isolated in korea was found to be much lower than that of p. aeruginosa , but its resistance rate rose from 4% in the first quarter to 20% in the third quarter of 2002 at the coordinating laboratory ( data not shown ) . in our study , mbl - producing pseudomonas spp . and acinetobacter spp . were isolated mainly from sputum and urine specimens , and most ( 81.7% ) isolates were from inpatients and intensive - care unit patients .
therefore , proper treatment of respiratory secretions and urine from intensive - care unit patients is considered an important aspect of preventing the spread of mbl - producing organisms .
the presence of p. aeruginosa isolates with identical pfge patterns among those collected not only from certain hospitals but also from different hospitals suggests that clonal spread is at least a part of the cause of intra- and inter - hospital dissemination of mbl - producing isolates .
reported that five of seven patients infected with mbl - producing p. aeruginosa died , although the cause of death was difficult to establish with certainty ( 16 ) .
clinical studies on the infection are rare because isolation of mbl - producing gram - negative bacilli increased only recently .
we anticipate difficulties in treating patients infected with mbl - producing gram - negative bacilli , which can hydrolyze , in vitro , all available -lactams , except aztreonam for which clinical efficacy is unknown .
our study indicates the urgent need for action to prevent further spread of mbl - producing organisms .
previous experiences with penicillin - nonsusceptible pneumococci , methicillin - resistant staphylococcus aureus , vancomycin - resistant enterococcus faecium , and extended - spectrum -lactamase  producing klebsiella pneumoniae indicate that once resistant bacteria can become widespread and can not be controlled ( 10 ) .
although the national committee for clinical laboratory standards document ( 12 ) does not contain procedures for detection , simple procedures are available ( 13 ) . the prevalence of blavim-2 allele - positive p. aeruginosa and blaimp-1 allele - positive acinetobacter spp .
is increasing possibly because of clonal and horizontal spread of the resistance determinant in korean hospitals .
sputum and urine from inpatients and intensive - care unit patients were found to be the main sources of mbl - producing isolates .
laboratories not only in korea but also in other countries with carbapenem - resistant organisms must be prepared to screen mbl - producing isolates to determine the clinical impact and prevent further spread of mbl - producing organisms .
 we determined the occurrence of acquired metallo--lactamase ( mbl)producing bacteria in korean hospitals . among the isolates 
 nonsusceptible to imipenem that were collected from 28 hospitals from 2000 to 2001 , 44 ( 11.4% ) of 387 pseudomonas spp . 
 and 38 ( 14.2% ) of 267 acinetobacter spp . 
 infections produced mbl and had alleles of blavim-2 or blaimp-1 . 
 mbl - producing isolates were detected in 60.7% of the hospitals . 
The Study
Conclusions