No abstract available.
Gram-Positive Cocci* ; Imipenem* ; Ofloxacin*

Minimal inhibitory concentrations (MICs) against piperacillin/tazobactam were determined on a total of 50 clinical isolates of imipenem resistant Pseudomonas aeruginosa (IRPA). MIC50 and MIC90 were 32microgram/mL and 512microgram/mL, respectively. The susceptibility of IRPA against piperacillin/tazobactam was 59%. Of the 50 IRPA strains, only two were PCR positive for blaVIM and none for blaIMP.
Imipenem ; Polymerase Chain Reaction ; Pseudomonas aeruginosa* ; Pseudomonas*

No abstract available.
Acinetobacter baumannii* ; Acinetobacter* ; Hospitals, General* ; Imipenem* ; Korea*

BACKGROUND: In our hospital, an abrupt increase in the resistant rate of A. baumannii to imipenem was observed. We evaluated the imipenem minimal inhibitory concentration (MIC) of an automated system that our laboratory is using, by comparing with those of other methods. METHODS: During the period from February 2002 to February 2003, the imipenem MICs of the agar dilution method, Etest(R), and the disk diffusion method, were compared for imipenem-resistant A. baumannii tested by an automated system in 46 samples at Chung-Ang University Phil-Dong Hospital. We tested for susceptibility to imipenem with the Vitek system by using the GNI card, the disk diffusion method by using the imipenem disk (BBL(TM)), and the agar dilution method. PCR testing of the isolates for carbapenemase genes (IMP-1 and VIM-2) detected in other hospitals was done using published primers and conditions. RESULTS: By the agar dilution method, 23 (50.0%) isolates were susceptible to imipenem, 14 (30.4%) isolates were intermediate, and 9 (19.6%) isolates were resistant. However, by the Etest, 8 (17.4%) were susceptible to imipenem, and 28 (60.9%) isolates were resistant. By the disk diffusion method, the susceptible isolates were 14 (30.4%) and the resistant isolates were 17 (37.0%). Quantitative agreement between the agar dilution method and the disk diffusion test gave an inverse linear correlation coefficient (r=-0.564). The results of the 13 isolates, whose results of the MIC were below 2 or above 16 in the agar dilution method, corresponded with the Etest and the disk diffusion test. The IMP-1 gene was detected in one isolate. CONCLUSIONS: It is recommended that when a gram-negative bacilli isolate including A. baumannii is characterized as resistant to imipenem by the Vitek system, an additional simple test, such as the disk diffusion assay, might be used.
Acinetobacter baumannii* ; Agar ; Diffusion ; Imipenem* ; Polymerase Chain Reaction

BACKGROUND: Multi-drug resistant (MDR) Acinetobacter baumannii has emerged as one of the most important nosocomial pathogens. In addition to the diverse resistance mechanisms, some A. baumannii strains are known to have biofilm-producing capacity, thereby decreasing antibiotic effectiveness. MATERIALS AND METHODS: This study was designed to assess biofilm-producing capacity of three different MDR A. baumannii strains with diverse resistance mechanisms (OXA-51, IMP-1 and VIM-2 type beta-lactamases), and intended to compare the effect of each antibiotic regimen (rifampicin, colistin, imipenem, tigecycline, rifampicin-imipenem and rifampicin-colistin) on mature A. baumannii biofilms using in vitro polystyrene plate biofilm assay. RESULTS: Among three MDR A. baumannii strains, only VIM-2 strain produced strong biofilm compared to the controls (optical density, 8.04 +/- 2.16 vs. 0.49 +/- 0.26). Regarding VIM-2 strains, none of imipenem, colistin and rifampicin reduced biofilm formation alone at MIC of each antibiotic agent (inhibition of biofilm synthesis, less than 30%). In comparison, tigecyclin (0.76 +/- 0.23), imipenem-rifampicin (1.07 +/- 0.31) and colistin-rifampicin (1.47 +/- 0.54) showed a significant inhibition of biofilm synthesis compared to the positive controls at 48 hours after incubation (P<0.01). Tigecycline inhibited biofilm formation even at the one fourth level of MIC (1.17 +/- 0.21). Likewise, both imipenem and colistin were also effective even with the reduced concentrations when those were combined with rifampicin. Such biofilm-inhibiting effects with those antibiotic regimens sustained up to 96 hours after incubation. CONCLUSION: Tigecycline, imipenem-rifampicin and colistin-rifampicin would be effective for the prevention or reduction of biofilm formation caused by A. baumannii strains.
Acinetobacter baumannii* ; Anti-Bacterial Agents ; Biofilms ; Colistin* ; Imipenem* ; Polystyrenes ; Rifampin*

BACKGROUND: Acinetobacter baumannii has been reported as a major cause of nosocomial infections with increasing frequency. Recently, the emergence of carbapenem-resistant strains has become a major problem in treatment. The use of nontraditional agents such as colistin and a combination therapy have been tried. The purpose of this study was to evaluate the activity of antimicrobial combinations against multidrug-resistant (MDR) A. baumannii. METHODS: Twenty-nine strains of MDR A. baumannii, either resistant or intermediate to imipenem, were collected from February 2003 to February 2004. Minimum inhibitory concentrations (MICs) were determined by the agar dilution method. The checkerboard method was used to assess the activity of ampicillin-sulbactam in combination with amikacin, tobramycin or meropenem and colistin in combination with ceftazidime, meropenem, or rifampin. RESULTS: The MIC90 of ceftazidime and cefepime were 2, 048 g/mL and 512 g/mL, respectively, while the MIC90 of colistin was 0.5 g/mL. The antimicrobial combinations that showed an additive effect for one or two strains were colistin with rifampin or ceftazidime and ampicillin-sulbactam with tobramycin or meropenem. Other antimicrobial combinations showed indifferent effects against most strains. There were no synergistic or antagonistic combinations. CONCLUSIONS: These data suggested that colistin may be an alternative drug for MDR A. baumannii. For the effective treatment of patients infected with these resistant strains, further studies are needed to evaluate antimicrobial combinations against a large number of heterogeneous isolates, and these studies must be followed by clinical trials.
Acinetobacter baumannii* ; Agar ; Amikacin ; Ceftazidime ; Colistin ; Cross Infection ; Humans ; Imipenem ; Microbial Sensitivity Tests ; Rifampin ; Tobramycin

BACKGROUND: The therapeutic difficulty due to wide-spread emergence of multiply resistant strains is a major problem in Pseudomonas aeruginosa infection. Carbapenem-resistant P. aeruginosa strains are being isolated with increasing frequency. Clinical isolates of P. aeruginosa with transferable imipen-em resistance due to production of metallo-beta-lactamase (MBL) have been reported. This study was performed to determine the usefulness of the imipenem-EDTA disk test to detect MBL, to examine the prevalence of MBL in a tertiary care hospital in Korea. METHODS: One hundred sixteen P. aeruginosa isolates with reduced susceptibilities to imipenem were collected during the period of 2000-2003 in the Samsung Medical Center. Imipenem-resistant P. aeruginosa isolates were examined for MBL production by imipenem-EDTA disk tests. To detect of blaIMP-1 , blaVIM-1, and blaVIM-2 genes, polymerase chain reactions (PCR) were performed and the positive isolates were confirmed by sequencing. RESULTS: Among 116 clinical isolates of P. aeruginosa, 20 isolates (17.2%) were positive for the imipenem-EDTA disk tests. Nineteen isolates (16.4%) carried VIM-2. Accoroding to PCR results, the sensitivity, specificity, and test efficiency of the imipenem-EDTA disk tests were 89%, 97%, and 96%, respectively. CONCLUSIONS: The imipenem-EDTA disk test is sensitive and specific for detecting VIM producer. VIM-2 may be an important MBL in P. aeruginosa in tertiary care hospitals the Korea. The spread of MBL genes could compromise the future usefulness of carbapenem for the treatment of gram-neg-ative bacilli infections.
Imipenem ; Korea ; Mass Screening* ; Polymerase Chain Reaction ; Prevalence ; Pseudomonas aeruginosa* ; Sensitivity and Specificity ; Tertiary Healthcare

BACKGROUND: Enterococcus faecium (E. faecium) is potential pathogens of mixed infections for which a broad-spectrum antimicrobial agents such as imipenem has a therapeutic role. But controversy continues concerning testing imipenem versus enterococci. The purpose of this study were 1) to investigate the ability of penicillin and ampicillin minimum inhibitory concentration (MIC) to predict in vitro susceptibility of E. faecium versus imipenem. and 2) to compare MICs of ampicillin, penicillin and imipenem by the Vitek system with those by agar dilution method. METHODS: Fifty-two isolates of E. faecium between April 2002 and May 2002 were tested. Each isolate was tested versus penicillin, ampicillin and imipenem. MICs were determined by Vitek system and agar dilution method according to NCCLS guidelines. Imipenem MIC determinations were repeated by E-test. RESULTS: MIC of Vitek system tends to be lower than that of agar dilution method, but there was good concordance between MICs of penicillin and ampicillin by Vitek system and agar dilution method. But for imipenem, the MICs by the agar dilution method did not correspond with the Vitek results. Of the 52 E. faecium isolates tested, in vitro activity of penicillin and ampicillin accurately predicts that of imipenem. CONCLUSIONS: MICs of ampicillin and penicillin are reliable, but imipenem MIC is not reliable for E. faecium by Vitek system. In vitro activity of penicillin and ampicillin versus E. faecium accurately predicts that of imipenem.
Agar ; Ampicillin ; Anti-Infective Agents ; Coinfection ; Enterococcus faecium* ; Enterococcus* ; Imipenem* ; Microbial Sensitivity Tests ; Penicillins

Carbapenemase production has been reported worldwide in gram-negative bacteria, including Acinetobacter species. We detected carbapenemase-producing Acinetobacter pittii in clinical isolates in Daejeon, Korea. Twenty-one ertapenem-resistant A. pittii isolates screened with a disk diffusion method were characterized by using the Epsilon test, four multiplex PCR assays, and a multilocus sequence typing (MLST) scheme. A total of 21 A. pittii isolates harbored the metallo-beta-lactamase (MBL) gene bla(IMP-1) or bla(NDM-1). Nineteen isolates containing bla(IMP-1) were resistant to imipenem and meropenem, but two isolates harboring bla(NDM-1) were susceptible to them. The sequence types (STs) of the two New Delhi MBL (NDM-1)-producing A. pittii isolates were ST70 and ST207, which differed from the STs (ST63, ST119, ST396, and a novel ST) of the IMP-1-producing A. pittii. This is the first report on NDM-1-producing A. pittii isolates in Korea. Our results emphasize that the study of NDM-1-producing gram-negative bacteria should involve carbapenem-susceptible as well as carbapenem-resistant isolates.
Acinetobacter* ; Diffusion ; Gram-Negative Bacteria ; Imipenem ; Korea ; Multilocus Sequence Typing ; Multiplex Polymerase Chain Reaction

BACKGROUND: Periodic monitoring of regional or institutional resistance trends of clinically important anaerobic bacteria is recommended, because the resistance of anaerobic pathogens to antimicrobial drugs and inappropriate therapy are associated with poor clinical outcomes. There has been no multicenter study of clinical anaerobic isolates in Korea. We aimed to determine the antimicrobial resistance patterns of clinically important anaerobes at multiple centers in Korea. METHODS: A total of 268 non-duplicated clinical isolates of anaerobic bacteria were collected from four large medical centers in Korea in 2012. Antimicrobial susceptibility was tested by the agar dilution method according to the CLSI guidelines. The following antimicrobials were tested: piperacillin, piperacillin-tazobactam, cefoxitin, cefotetan, imipenem, meropenem, clindamycin, moxifloxacin, chloramphenicol, metronidazole, and tigecycline. RESULTS: Organisms of the Bacteroides fragilis group were highly susceptible to piperacillin-tazobactam, imipenem, and meropenem, as their resistance rates to these three antimicrobials were lower than 6%. For B. fragilis group isolates and anaerobic gram-positive cocci, the resistance rates to moxifloxacin were 12-25% and 11-13%, respectively. Among B. fragilis group organisms, the resistance rates to tigecycline were 16-17%. Two isolates of Finegoldia magna were non-susceptible to chloramphenicol (minimum inhibitory concentrations of 16-32 mg/L). Resistance patterns were different among the different hospitals. CONCLUSIONS: Piperacillin-tazobactam, cefoxitin, and carbapemems are highly active beta-lactam agents against most of the anaerobes. The resistance rates to moxifloxacin and tigecycline are slightly higher than those in the previous study.
Agar ; Bacteria, Anaerobic* ; Bacteroides fragilis ; Cefotetan ; Cefoxitin ; Chloramphenicol ; Clindamycin ; Gram-Positive Cocci ; Imipenem ; Korea ; Metronidazole ; Piperacillin