BACKGROUND/AIMS: The inhibitory effects of the combination of beta-lactam with ciprofloxacin or amikacin against clinical isolates of multidrug-resistant Pseudomonas aeruginosa were evaluated. METHODS: This study examined ten isolates with variable levels of resistance to ceftazidime, cefepime, piperacillin/tazobactam, meropenem, ciprofloxacin, and amikacin. The efficacy of the combined antibiotics was studied using a checkerboard method or in vitro killing assay. RESULTS: The combination of ceftazidime, cefepime, aztreonam, piperacillin-tazobactam, or meropenem with amikacin showed synergistic effects for all of the strains regardless of the minimum inhibitory concentration (MIC) of amikacin, but combination with ciprofloxacin showed a synergistic effect for the isolate with a low MIC of ciprofloxacin by the checkerboard method. The isolates with a high MIC of ciprofloxacin showed an indifferent effect in combination with beta-lactam and ciprofloxacin. The in vitro killing assay showed that meropenem with ciprofloxacin acted synergistically for the isolates with a MIC of 16 microgram/mL of ciprofloxacin. However, amikacin showed synergistic effects with meropenem for the isolates with high-level resistance against amikacin, i.e., up to an MIC of 128 microgram/mL. Contrary to the checkerboard method results, no synergy was observed for the combination of ceftazidime/piperacillin-tazobactam and amikacin. CONCLUSIONS: Meropenem with amikacin can be the first choice for infections caused by multidrug-resistant P. aeruginosa when the level of resistance is not known.
Amikacin ; Anti-Bacterial Agents ; Aztreonam ; Ceftazidime ; Cephalosporins ; Ciprofloxacin ; Homicide ; Microbial Sensitivity Tests ; Pseudomonas ; Pseudomonas aeruginosa ; Thienamycins

BACKGROUND: The prevalence of extended-spectrum -lactamase (ESBL)-producing Klebsiella pneumoniae and Escherichia coli has been increased in Korea, but the testing and reporting ESBL-mediated resistance remains unclear. We undertook a study to evaluate the method to screen isolates of ESBL-producing K. pneumoniae and E. coli using cefpodoxime disk. METHODS: Fifty-eight strains of K. pneumoniae and 28 strains of E. coli were tested for production of ESBLs by the double disk synergy test. Susceptibility to cefpodoxime, ceftazidime, cefotaxime, and aztreonam was determined by disk diffusion method. RESULTS: All strains that produced ESBLs were resistant to cefpodoxime, whereas those that not produced ESBLs were susceptible (97%) to this agents. The disk diffusion test exhibited 100% sensitivity and 97% specificity when NCCLS conventional interpretive criteria were used. All other oxyimino- -lactam agents tested were inferior discriminators between the two groups of organisms. When NCCLS ESBL interpretive criteria were used, the disk diffusion test using cefpodoxime exhibited 100% sensitivity and 83% specificity. CONCLUSIONS: Routine disk diffusion susceptibility test with cefpodoxime disk (10g) can be used to detect strains of ESBL-producing K. pneumoniae and E. coli without include supplemental testing for ESBL production.
Aztreonam ; Cefotaxime ; Ceftazidime ; Diffusion ; Escherichia coli* ; Escherichia* ; Klebsiella pneumoniae* ; Klebsiella* ; Korea ; Pneumonia ; Prevalence ; Sensitivity and Specificity

BACKGROUND: Escherichia coli and Klebsiella pneumoniae resistant to 3rd generation cephalosporin have been reported with increasing frequency in tertiary-care hospital in Korea. MicroScan Neg Combo Panel Type 21 (Type 21) contains a 1 microgram/mL cepfodoxime (POD) in addition to other screen wells containing ceftazidime, cefotaxime, ceftriaxone, and aztreonam, which are designed for detecting extended-spectrum beta-lactamase (ESBL)-producing E. coli and Klebsiella species. We evaluated the Type 21 panel for its ability to detect ESBL. METHODS: From November to December in 1998, 496 E. coli and 326 K. pneumoniae strains isolated from clinical specimens were tested with Type 21 panel The isolates flagged as ESBL producers by the panel were confirmed by the double disk synergy test (DDS). To evaluate the specificity of POD, n-lactamases of 54 E, coli and 20 K. pneumoniae strains that were flagged by, POD only from January to May 1999 were analyzed by isoelectric focusing(IEF). RESULTS: 75/496(15%) E. coli and 68/326(21%) K. pneumoniae were flagged as ESBL producers by Type 21 panel. Of those, 94 isolates including 38/75 (51%) of E. coli and 56/68 (82%) of K. pneumoniae were positive for DDS. Among the 94 ESBL producers, all were detected by POD, 84% by cefotaxime, 85% by ceftazidime, 84% by ceftriaxone, and 86% by aztreonam. The 74 strains that were flagged as ESBL producers by POD screen well only were mostly DDS-negative, cefoxitin- resistant and showed beta-lactamases with pls of 5.4 and 7.6 or no band, which could be interpreted as the presence of TEM-1 or SHV-1 type beta-lactamases and/or basal AmpC beta-lactamases, not ESBL. CONCLUSION: MicroScan Neg Combo Panel Type 21 was able to detect a greater number of ESBL producers by inclusion of POD in its screening well. However, the specificity of POD was compromised by flagging a significant number of DDS negative strains. We conclude that the isolates with reduced susceptibility to 3rd generation cephalosporins as well as POD can be reported as ESBL-producers and those resistant to POD only should be confirmed by DDS.
Aztreonam ; beta-Lactamases ; Cefotaxime ; Ceftazidime ; Ceftriaxone ; Cephalosporins ; Escherichia coli ; Klebsiella ; Klebsiella pneumoniae ; Korea ; Mass Screening ; Pneumonia ; Sensitivity and Specificity

BACKGROUND: In 2010, the Clinical and Laboratory Standards Institute (CLSI) revised the minimum inhibitory concentration (MIC) breakpoints of cephalosporins and aztreonam to exempt extended-spectrum beta-lactamase (ESBL) confirmatory tests for Enterobacteriaceae. However, the CLSI did not change the MIC breakpoint of cefepime. Here, a proficiency survey of a strain of ESBL-producing Klebsiella pneumoniae was analyzed for MIC distribution and interpretation of cephalosporins and aztreonam. METHODS: The survey strain, K. pneumoniae, which produced SHV-18, was distributed to 170 clinical laboratories as 1 of 5 presumptive clinical specimens through the proficiency survey of the clinical microbiology division of the Korean Association of Quality Assurance for Clinical Laboratories (KAQACL). MIC, zone diameter of inhibition (ZDI), and interpretation of tested antimicrobials, methods of antimicrobial susceptibility testing (AST), and ESBL confirmatory results were collected. RESULTS: According to the revised breakpoints of the 2010 CLSI guidelines, MIC results indicated resistance to aztreonam in 100%, cefepime in 5.5%, cefotaxime in 20%, ceftazidime in 100%, and ceftriaxone in 100% of samples by broth microdilution methods. ZDI results also indicated resistance to aztreonam in 75%, cefepime in 0%, cefotaxime in 66.7%, ceftazidime in 100%, and ceftriaxone in 80% of samples by disk diffusion method. Ninety (75.6%) participants performed an ESBL confirmatory test, and 89 (98.9%) reported ESBL-positive tests. Of the 55 laboratories that tested the susceptibility of cefepime, 50 (90.9%) self-reported to be "resistant" because of ESBL-positive results. CONCLUSIONS: In conclusion, susceptibility testing of ESBL producers against certain cephalosporins is not reliable enough to apply the revised breakpoints presented in the 2010 CLSI guidelines. It is therefore necessary to reach a consensus for interpretation of ASTs of ESBL producers in Korea. Ideally, clinicians should be provided two interpretations based on both the revised breakpoints and ESBL confirmatory testing.
Aztreonam ; beta-Lactamases ; Cefotaxime ; Ceftazidime ; Ceftriaxone ; Cephalosporins ; Consensus ; Diffusion ; Enterobacteriaceae ; Klebsiella ; Klebsiella pneumoniae ; Korea ; Microbial Sensitivity Tests ; Pneumonia ; Sprains and Strains

BACKGROUND: Accurate detection of extended spectrum beta-lactamase (ESBL) is important because ESBLs producing organisms may appear susceptible to oxyimino-beta-lactams in standard susceptibility tests, but are considered to be clinically resistant to these drugs. Conventional antimicrobial susceptibility test methods do not reliably detect ESBL production. Molecular techniques and NCCLS broth dilution method, which detect ESBL production, may be time consuming, expensive and technically difficult to perform. The purpose of this study is to evaluate the clinical usefulness of NCCLS ESBL phenotypic confirmatory test by disk diffusion method. METHODS: For 96 Escherichia coli and 49 Klebsiella pneumoniae isolates collected between December 2000 to February 2001, double disk synergy test, NCCLS ESBL screening and phenotypic confirmatory test by disk diffusion test were performed. The ESBL producer was defined as organism showed an increase in the zone diameter of > or = 5 mm for either antimicrobial agent such as cefotaxime and ceftazidime tested in combination with clavulanic acid versus its zone when tested alone. RESULTS: The sensitivity of NCCLS ESBL phenotypic confirmatory test were as follows: cefotaxime/clavulanic acid disk; 100% in K. pneumoniae and 83% in E. coli, and ceftazidime/clavulanic acid disk; 94% in K. pneumoniae and 67% in E. coli, respectively. Among the organisms with positive to NCCLS ESBL phenotypic confirmatory test, the detection rate of antimicrobial agents in double disk synergy test were as follows: K. pneumoniae; cefotaxime (84%), aztreonam (74%), and ceftazidime (52%), and E. coli; cefotaxime (44%), ceftazidime (44%), and aztreonam (39%). CONCLUSIONS: The NCCLS ESBL phenotypic confirmatory test by disk diffusion method is easy, rapid, and sensitive method, suitable for routine use in the clinical laboratory.
Anti-Infective Agents ; Aztreonam ; beta-Lactamases* ; Cefotaxime ; Ceftazidime ; Clavulanic Acid ; Diffusion ; Escherichia coli* ; Escherichia* ; Klebsiella pneumoniae* ; Klebsiella* ; Mass Screening ; Pneumonia

BACKGROUND: Because extended-spectrum -lactamase (ESBL) producing strains can frequent-ly cause therapeutic failure and infectious outbreaks in hospitals, rapid and accurate detection of these strains are important. We compared the Vitek ESBL test with the NCCLS ESBL phenotypic confirmatory test by disk diffusion (NCCLS ESBL test) and double disk synergy test (DDST). METHODS: For a total of 316 clinical isolates composed of Escherichia coli (184), Klebsiella pneu-moniae (120) and Klebsiella oxytoca (12), we performed the Vitek ESBL test and the NCCLS ESBL test. For sixty-eight ESBL producing isolates, the Vitek ESBL test was compared with the NCCLS ESBL test and the DDST. The ESBL producer was defined as an organism showing an increase in the inhibited zone diameter of >or=5 mm for either cefotaxime or ceftazidime in combination with clavu-lanic acid versus its single test. The DDST was performed with 20 mm and 30 mm for interdisk diam-eter. For seven false negative isolates in the Vitek ESBL test, the DDST of cefepime was performed. RESULTS: Compared with the NCCLS ESBL test, the Vitek ESBL test showed one false positive (specificity, 99.6%), seven false negatives (sensitivity, 89.7%) and 97.5% agreement. Seven false negative isolates of the Vitek ESBL test were the cefoxitin-resistant ESBL producer. In positivity for the NCCLS ESBL test of 68 ESBL producing isolates, cefotaxime-clavulanic acid and ceftazidime-clavulanic acid were 94% and 91%. Cefotaxime, ceftazidime, aztreonam and ceftriaxone showed 95/90%, 100/55%, 100/85% and 95/80% positivity in double-disk synergy with amoxicillin-clavulanic acid (AMC) for 20/30 mm of the interdisk diameter respectively. For seven false negative isolates of the Vitek ESBL test, cefepime showed a distinct synergic effect with AMC. CONCLUSIONS: The Vitek ESBL test may be a useful method for clinical laboratories due to its easy, rapid and sensitive method but its method was less sensitive to cefoxitin-resistant ESBL. For these cases, if the NCCLS ESBL test or DDST with cefepime are added, the detection rate of the ESBL pro-ducer can be augmented.
Amoxicillin-Potassium Clavulanate Combination ; Aztreonam ; Cefotaxime ; Ceftazidime ; Ceftriaxone ; Diffusion ; Disease Outbreaks ; Escherichia coli* ; Escherichia* ; Klebsiella oxytoca ; Klebsiella*

BACKGROUND: The recently issued Korean version of antimicrobial susceptibility cards for Vitek 2 system uses an adjusted antimicrobial combination that reflects Korean clinical practice and CLSI guidelines. We evaluated the two Korean antimicrobial susceptibility testing cards for gram negative rods, AST N056 and AST N055. METHODS: The results of susceptibility tests were compared between the original and Korean cards. A number of the same antimicrobials included in the both cards were 15 in AST N041-AST N056 and 17 in AST N022-AST N055. Susceptibilities to the newly added antimicrobials, aztreonam, tobramycin, and meropenem for AST N056; and cefotaxime, levofloxacin, and minocycline for AST N055 were compared with those obtained by disc diffusion test and, in case of discrepancy, by confirmative Etest or broth dilution method. RESULTS: In comparison between AST N041 and AST N056 cards, the average discrepancy rate per strain was 0.34, minor error was 88.2%, and major error and very major error were both 5.9%. In comparison between AST N022 and AST055 cards, the average discrepancy rate per strain and very major error were 1.23 and 4.4%, respectively. The three antimicrobial agents added into AST N055 card showed highly discrepant results as a total of 49 items (44.1%) in 111 isolates were discrepant with very major error of 5.9% and major error of 2.0%. CONCLUSION: AST N056 showed acceptable results in most items including the newly added antimicrobial agents. However, in the case of AST N055 card that showed a relatively high discrepancy, other indicator antibiotics should be referred to for newly added three antimicrobials. For the antibiotics that showed a high discrepancy between the original and Korean cards, a comparison study should be performed using the standard method and clinical isolates collected in Korea.
Anti-Bacterial Agents ; Anti-Infective Agents ; Aztreonam ; Cefotaxime ; Diffusion ; Enterobacteriaceae ; Korea ; Minocycline ; Ofloxacin ; Sprains and Strains ; Thienamycins ; Tobramycin

Major pathogenic Gramnegative organisms such as P. aeruginosa, Serratia species, E. coli, Enterobacter species which are isolated from the specimens in large medical centers are greatly resistant to the commonly used antibiotics. Gramnegative bacilli, which had been isolated in Yeungnam Uni rersity Hospital during the period from December 1992 to April 1993 and turned out to be resistant to the primary antibiotics susceptibility test for chloramphenicoi, ampicillin, eephaiothin,- geniamicitt, tetracyclin, amikin and tobramycin, were subjected to the secondary antibiotics susceptibility test for aztreonam, ceftazidime, ciprofloxacine, cefotaxime, cefamandole, piperacillin, ticarcillin and sulfamethoxazole trimethopime. Out of 315 tested organisms, 167 organisms (53%) were resistant to all secondary antibiotics in vitro. Antimicrobial activity of ceftazidime (37.1%), aztreonam (11. %), ciprofloxacine (7.9%) against Gram negative bacilli were slightly more active than other antibiotics tested, while cefamandole was not active to all the Gramnegative bacilli tested. According to the specimens, E. coli was the most frequently resistant organisms to the primary antibiotics from urine, A. baumanii, from respiratory system and wounds, and P. aeruginosa from various specimens. In summary, Gram negative bacilli resistant to the primarily applied antibiotics also were resistant to the secondary antibiotics. Rearrangement of the antibiotics disks for the antibiotic susceptibility test should be considered.
Amikacin ; Ampicillin ; Anti-Bacterial Agents* ; Aztreonam ; Cefamandole ; Cefotaxime ; Ceftazidime ; Ciprofloxacin ; Enterobacter ; Piperacillin ; Respiratory System ; Serratia ; Sulfamethoxazole ; Ticarcillin ; Tobramycin ; Wounds and Injuries

BACKGROUND: Pseudomonas aeruginosafrequently causes nosocomial infection. Recently, there have been reports of infection with multidrug-resistant P. aeruginosa. The purpose of this study was to evaluate the in vitro effect of antimicrobial combination against multidrug-resistant P. aeruginosa. METHODS: Twenty isolates of imipenem and/or cefepime resistant P. aeruginosa were collected from the microbiology laboratory of Ewha Womans Unversity Mokdong Hospital. Checkerboard titration method was used to assess the activity of ceftazidime or cefepime in combination with amikacin, gentamicin or aztreonam, and colistin in combination with ceftazidime or rifampin. RESULTS: All isolates were resistant to more than 12 antimicrobial agents including imipenem and/or cefepime by broth microdilution method; however, no isolates were resistant to colistin. Most of the isolates showed high level resistance to ceftazidime, cefepime and meropenem, with MIC90 of 128, 512 and 64 microgram/mL, respectively. The MIC90 of colistin was 2 microgram/mL, which is within the su ceptiblerange. Synergistic effect was not detected by the checkerboard titration method with any antimicrobial combinations. However, a partial synergy was observed in 40% of the isolates with the combination of ceftazidime and amikacin, 65% with ceftazidime and gentamicin, 45% with cefepime and amikacin, and 75% with cefepime and gentamicin. Other antimicrobial combinations showed indifference against most strains, and antagonism was not observed. CONCLUSION: Multidrug-resistant P. aeruginosa isolates were all susceptible to colistin. The combined regimens of ceftazidime with amikacin or gentamicin and cefepime with amikacin or gentamicin revealed a partially synergistic effect in 40-75% of the isolates.
Amikacin ; Anti-Infective Agents ; Aztreonam ; Ceftazidime ; Colistin ; Cross Infection ; Female ; Gentamicins ; Humans ; Imipenem ; Korea* ; Pseudomonas aeruginosa* ; Pseudomonas* ; Rifampin

An increasing prevalence of infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa (P. aeruginosa) causes a serious therapeutic problem in clinical setting. This study investigated the antimicrobial susceptibility, resistance mechanisms against aminoglycosides, and molecular epidemiology of 76 blood isolates of P. aeruginosa from two Korean hospitals. Thirty-four isolates were susceptible to all 13 antimicrobial agents tested, whereas 28 isolates showed a MDR or extensively drug-resistant phenotype. There was a significant difference in resistance rates of P. aeruginosa isolates against aztreonam, piperacillin-tazobactam, imipenem, meropenem, ciprofloxacin, and norfloxacin between two hospitals. Genes for aminoglycoside-modifying enzymes (AMEs), including aphA6 (n = 14), aadB (n = 11), aacA4 (n = 8), and aphA1 (n = 1), and 16S rRNA methylase armA (n = 6) were detected in 26 P. aeruginosa isolates resistant to aminoglycosides. There was no significant difference in carriage of genes for AME and 16S rRNA methylase between two hospitals, but aacA4 and aphA1 were specifically detected in P. aeruginosa isolates from one hospital. Seventy-six P. aeruginosa isolates were classified into 55 pulsotypes at similarity value of 0.85, and 31 and 24 pulsotypes were specifically detected in each hospital. This study demonstrates that differences in antimicrobial susceptibility of P. aeruginosa isolates between two hospitals are possibly due to the presence of diverse clones specific in each hospital.
Aminoglycosides ; Anti-Infective Agents ; Aztreonam ; Ciprofloxacin ; Clone Cells ; Imipenem ; Molecular Epidemiology ; Norfloxacin ; Phenotype ; Prevalence ; Pseudomonas aeruginosa* ; Pseudomonas*