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This review addresses the escalating challenge posed by antibiotic resistance, highlighting its profound impact on global public health, including increased mortality rates and healthcare expenditures. The review focuses on the need to adopt the One Health approach to effectively manage antibiotic usage across human, animal, and environmental domains. Antimicrobial stewardship programs (ASPs) are considered as comprehensive strategies that encompass both core and supplementary initiatives aimed at enhancing prudent antibiotic use. The 2021 "Guidelines on Implementing ASP in Korea" introduced such strategies, with a strong emphasis on fostering multidisciplinary and collaborative efforts. Furthermore, the "Core Elements for Implementing ASPs in Korean General Hospitals," established in 2022, provide a structured framework for ASPs, delineating leadership responsibilities, the composition of interdisciplinary ASP teams, a range of interventions, and continuous monitoring and reporting mechanisms. In addition, this review examines patient-centric campaigns such as "Speak Up, Get Smart" and emphasizes the pivotal role of a multidisciplinary approach and international cooperation in addressing the multifaceted challenges associated with antibiotic resistance.

Background: Antimicrobial prescriptions for serious chronic or acute illness nearing its end stages raise concerns about the potential for futile use, adverse events, increased multidrug-resistant organisms, and significant patient and social cost burdens. This study investigated the nationwide situation of how antibiotics are prescribed to patients during the last 14 days of life to guide future actions., Methods: This nationwide multicenter retrospective cohort study was conducted at 13 hospitals in South Korea from November 1 to December 31, 2018. All decedents were included in the study. Antibiotic use during the last two weeks of their lives was investigated., Results: A total of 1,201 (88.9%) patients received a median of two antimicrobial agents during the last two weeks of their lives. Carbapenems were prescribed to approximately half of the patients (44.4%) in the highest amount (301.2 days of therapy per 1,000 patient-days). Among the patients receiving antimicrobial agents, 63.6% were inappropriate and only 327 patients (27.2%) were referred by infectious disease specialists. The use of carbapenem (odds ratio [OR], 1.51; 95% confidence interval [CI], 1.13-2.03; P = 0.006), underlying cancer (OR, 1.56; 95% CI, 1.20-2.01, P = 0.047), underlying cerebrovascular disease (OR, 1.88; 95% CI, 1.23-2.89, P = 0.004), and no microbiological testing (OR, 1.79; 95% CI, 1.15-2.73; P = 0.010) were independent predictors for inappropriate antibiotic prescribing., Conclusion: A considerable number of antimicrobial agents are administered to patients with chronic or acute illnesses nearing their end-of-life, a high proportion of which are prescribed inappropriately. Consultation with an infectious disease specialist, in addition to an antimicrobial stewardship program, may be necessary to induce the optimal use of antibiotics., Competing Interests: The authors have no potential conflicts of interest to disclose., (© 2023 The Korean Academy of Medical Sciences.)

Background/aims: To investigate epidemiologic characteristics, clinical and economic burdens, and factors associated with mortality in complicated skin and skin structure infection (cSSSI) patients in Korea., Methods: A retrospective, observational, nationwide study was conducted between April to July 2012 at 14 tertiary-hospitals in Korea. Eligible patients were hospitalized adults with community acquired cSSSI, who underwent surgical intervention and completed treatment between November 2009 and October 2011. Data on demography, clinical characteristics, outcomes and medical resource utilization were collected through medical record review. Direct medical costs were calculated by multiplying quantities of resources utilized by each unit price in Korea., Results: Of 473 patients enrolled, 449 patients (except 24 patients with no record on surgical intervention) were eligible for analysis. Microbiological testing was performed on 66.1% of patients and 8.2% had multiple pathogens. Among culture confirmed pathogens (n = 297 patients, 340 episodes), 76.2% were gram-positive (Staphylococcus aureus; 41.2%) and 23.8% were gram-negative. The median duration of hospital stay was 16 days. Among treated patients, 3.3% experienced recurrence and 4.2% died in-hospital. The mean direct medical costs amounted to $4,195/ person, with the greatest expenses for hospitalization and antibiotics. The in-hospital mortality and total medical costs were higher in combined antibiotics therapy than monotherapy (p < 0.05). Charlson's comorbidity index ≥ 3, standardized early warning scoring ≥ 4, sub-fascia infections and combined initial therapy, were all found to be associated with higher mortality., Conclusion: Korean patients with community-onset cSSSI suffer from considerable clinical and economic burden. Efforts should be made to reduce this burden through appropriate initial treatment.

In 2019, a project designed to develop a system for measuring and comparing antibiotic usage in hospitals was launched in Korea. As part of this project, we developed a means to classify antibiotic usage in Korean hospitals using a modified Delphi method. In results, the following categories of antibiotic classification were accepted for use in Korean hospitals: 1) broad-spectrum antibacterial agents predominantly used for hospital-onset infections in adults, 2) broad-spectrum antibacterial agents predominantly used for community-acquired infections in adults, 3) antibacterial agents predominantly used for resistant gram-positive infections in adults, 4) narrow-spectrum beta-lactam agents in adults, 5) antibacterial agents predominantly used for extensive antibiotic resistant gram-negative bacteria in adults, and 6) total antibacterial agents., Competing Interests: The authors have no potential conflicts of interest to disclose., (© 2020 The Korean Academy of Medical Sciences.)

Background: This study evaluated the antimicrobial susceptibility of pathogens isolated from Korean patients with intraabdominal infections (IAIs)., Methods: This multicenter study was conducted at 6 university-affiliated hospitals in Korea between 2016 and 2018. All patients with microbiologically proven IAIs were retrospectively included, while patients with spontaneous bacterial peritonitis or continuous ambulatory peritoneal dialysis peritonitis were excluded. Identification and antimicrobial susceptibility testing were performed using automated microbiology systems., Results: A total of 2,114 non-duplicated clinical isolates were collected from 1,571 patients. Among these pathogens, 510 (24.1%) were isolated from nosocomial infections, and 848 isolates (40.1%) were associated with complicated IAIs. The distribution of the microorganisms included aerobic gram-negative (62.6% of isolates), aerobic gram-positive (33.7%), anaerobic (0.9%), and fungal (2.8%) pathogens. The most common pathogens were Escherichia coli (23.8%), followed by Enterococcus spp. (23.1%) and Klebsiella spp. (19.8%). The susceptibility rates of E. coli and Klebsiella spp. to major antibiotics were as follows: amoxicillin/clavulanate (62.5%, 83.0%), cefotaxime (61.4%, 80.7%), ceftazidime (63.7%, 83.1%), cefepime (65.3%, 84.3%), ciprofloxacin (56.4%, 86.3%), piperacillin/tazobactam (99.0%, 84.8%), amikacin (97.4%, 98.3%), and imipenem (99.8%, 98.8%). The susceptibility rates of Enterococcus spp. to ampicillin were 61.0%, amoxicillin/clavulanate, 63.6%; ciprofloxacin, 49.7%; imipenem, 65.2%; and vancomycin, 78.2%. The susceptibility rates of Pseudomonas aeruginosa and Acinetobacter spp. to imipenem were 77.4% and 36.7%, respectively., Conclusion: Enterococcus spp. with susceptibility to limited antibiotics was one of the main pathogens in Korean IAIs, along with E. coli and Klebsiella spp., which were highly susceptible to imipenem, amikacin, and piperacillin/tazobactam. Meanwhile, the low susceptibilities of E. coli or Klebsiella spp. to amoxicillin/clavulanate, advanced-generation cephalosporins, and ciprofloxacin should be considered when determining empirical antibiotic therapy in clinical practice., Competing Interests: The authors have no potential conflicts of interest to disclose., (© 2019 The Korean Academy of Medical Sciences.)

The aim of this study was to evaluate the changing pattern of antibiotic usage and antimicrobial resistance of bacterial pathogens among hospitalized patients in Korea. We simultaneously investigated the correlation between antimicrobial resistance and antibiotic consumption.Data on total antibiotic prescriptions, patient days, and antimicrobial sensitivity tests among inpatients from 6 university hospitals in Korea in 2004, 2008, and 2012 were collected. The consumption of each antibiotic class was converted to defined daily dose/1000 patient-days by using the anatomical therapeutic chemical classification system by the World Health Organization. We defined third-generation cephalosporins (3rd CEPs), fourth-generation cephalosporins, beta-lactam/beta-lactamase inhibitors, and fluoroquinolones (FQs) as broad-spectrum antibiotics and carbapenems, tigecycline, glycopeptides, oxazolidinone, and polymyxin as antibiotics against multidrug-resistant (MDR) pathogens.A 15.1% decrease in total antibiotic consumption was observed in 2012 compared to that observed in 2004. In contrast, a 10.2% and 70.7% increase in broad-spectrum antibiotics and antibiotics against MDR pathogens were observed, respectively, in the same period. The resistance rate of Escherichia coli to 3rd CEPs (17.6% in 2004, 21.7% in 2008, and 33.8% in 2012, P <.001) and ciprofloxacin (37.5% in 2004, 38.7% in 2008, and 46.6% in 2012, P = .001) demonstrated a significantly increasing trend. Similarly, the resistance rate of Klebsiella pneumoniae to 3rd CEPs (34.3% in 2004, 33.7% in 2008, and 44.5% in 2012, P <.001) gradually increased. Resistance of Acinetobacter baumanii and Pseudomonas aeruginosa to imipenem significantly increased throughout the study period (A baumanii: 8.9% in 2004, 40.8% in 2008, and 65.3% in 2012, P <.001; P aeruginosa: 25.1% in 2004, 31.5% in 2008, and 29.7% in 2008, P = .050).The consumption of carbapenems and FQs demonstrated significant positive correlation for resistance of E coli or K pneumoniae to 3rd CEPs as well as E coli or K pneumoniae to ciprofloxacin. Increasing resistance of A baumanii to ciprofloxacin was significantly correlated with increasing consumption of FQs; increasing resistance of A baumanii to imipenem was significantly correlated with increasing consumption of carbapenems.In conclusion, overall antimicrobial resistance increased and consumption of broad-spectrum antibiotics and antibiotics against MDR pathogens subsequently increased in Korean hospitals.

Genes encoding ciprofloxacin resistance in enterococci in animals may be transferred to bacteria in the animal gut and to zoonotic bacteria where they could pose a human health hazard. The objective of this study was to characterize antimicrobial resistance in high-level ciprofloxacin-resistant (HLCR) Enterococcus faecalis and Enterococcus faecium isolated from retail chicken meat. A total of 345 enterococci (335 E. faecalis and 10 E. faecium) were isolated from 200 chicken meat samples. Of these, 85 E. faecalis isolates and 1 E. faecium isolate were confirmed as HLCR enterococci. All 86 HLCR enterococci displayed gyrA- parC point mutations consisting of S83I-S80I (94.2%, 81 isolates), S83F-S80I (2.3%, 2 isolates), S83Y-S80I (2.3%, 2 isolates), and S83Y-S80F (1.2%, 1 isolate). Sixty-one (72.9%) of the 86 HLCR enterococci showed multidrug resistance to three to six classes of antimicrobial agents. Multilocus sequence typing revealed that E. faecalis had 17 different sequence types (ST) and E. faecium had 1 different ST, with ST256 observed most often (44 isolates, 51.8%). Although these results cannot exclude the possibility that pathotypes of enterococci isolated from chicken might represent transmission to or from humans, the foodborne HLCR E. faecalis indicated that the food chain is a potential route of enterococcal infection in humans.

Background: The purported value of empirical therapy to cover methicillin-resistant Staphylococcus aureus (MRSA) has been debated for decades. The purpose of this study was to evaluate the effects of inappropriate empirical antibiotic therapy on clinical outcomes in patients with healthcare-associated MRSA bacteremia (HA-MRSAB)., Methods: A prospective, multicenter, observational study was conducted in 15 teaching hospitals in the Republic of Korea from February 2010 to July 2011. The study subjects included adult patients with HA-MRSAB. Covariate adjustment using the propensity score was performed to control for bias in treatment assignment. The predictors of in-hospital mortality were determined by multivariate logistic regression analyses., Results: In total, 345 patients with HA-MRSAB were analyzed. The overall in-hospital mortality rate was 33.0 %. Appropriate empirical antibiotic therapy was given to 154 (44.6 %) patients. The vancomycin minimum inhibitory concentrations of the MRSA isolates ranged from 0.5 to 2 mg/L by E-test. There was no significant difference in mortality between propensity-matched patient pairs receiving inappropriate or appropriate empirical antibiotics (odds ratio [OR] = 1.20; 95 % confidence interval [CI] = 0.71-2.03). Among patients with severe sepsis or septic shock, there was no significant difference in mortality between the treatment groups. In multivariate analyses, severe sepsis or septic shock (OR = 5.45; 95 % CI = 2.14-13.87), Charlson's comorbidity index (per 1-point increment; OR = 1.52; 95 % CI = 1.27-1.83), and prior receipt of glycopeptides (OR = 3.24; 95 % CI = 1.08-9.67) were independent risk factors for mortality., Conclusion: Inappropriate empirical antibiotic therapy was not associated with clinical outcome in patients with HA-MRSAB. Prudent use of empirical glycopeptide therapy should be justified even in hospitals with high MRSA prevalence.

Although most Klebsiella pneumoniae liver abscesses have been reported to be monomicrobial, clinical outcomes have not been compared between antimicrobial therapy with and without anti-anaerobic coverage. A propensity score-matched cohort study was conducted using the 731 cases of K. pneumoniae liver abscess. Clinical outcomes were compared between a group discontinuing anti-anaerobic agents after K. pneumoniae identification and a group continuing. A total of 170 cases were matched at a 1:1 ratio using their propensity to discontinue anti-anaerobic agents. The McNemar's test showed no difference in mortality rates (1.8% for discontinuation versus 2.3% for continuation; P = 1.00) or relapse (1.8% versus 2.9%; P = 0.73) between groups. Early discontinuation of anti-anaerobic agents had no association with treatment failure by means of the generalized estimating equation model (odds ratio 0.48; P = 0.14) and the Kaplan-Meier method (P = 0.85) in matched groups. Early discontinuation of anti-anaerobic agents does not affect the clinical outcomes of patients with K. pneumoniae liver abscess., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Cefazolin is a common antibiotic for methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. Type A or C β-lactamase-producing MSSA frequently shows the cefazolin inoculum effect (CIE). However, the clinical implication of the CIE for MSSA bacteremia is obscure., Methods: MSSA bacteremic patients treated with cefazolin were included in a retrospective cohort study. The blaZ gene of the isolates was sequenced to identify the type of β-lactamase. The patients whose isolates showed a ≥4-fold increase in cefazolin, the minimal inhibitory concentration (MIC) at the high inoculum (∼5×10(7) CFU/ml), were assigned to the CIE-positive group and the remainder to the CIE-negative group. Treatment failure was assessed at 12 weeks after cefazolin was initiated., Results: A total of 113 MSSA bacteremic patients were included. Among the 113 isolates, 57.5% showed the CIE and 77.9% carried the blaZ gene; type A β-lactamase was 15.0% and type C was 40.7%. Persistent bacteremia was more common in the CIE-positive group (9% vs. 0%, p=0.04). Treatment failure rates were higher in the CIE-positive group with high bacterial burden infection, but the difference was not significant (48% vs. 25%, p=0.13). There was no significant difference of failure between groups with high-inoculum MIC ≥16 and ≤1 μg/ml (13% vs. 5%, p=0.31). In the multivariable analysis, underlying cardiovascular diseases, pneumonia, osteoarticular infections, and endocarditis were significant risk factors for treatment failure and the CIE was not significantly associated with treatment failure., Conclusion: The CIE might be associated with persistent bacteremia if cefazolin is used for MSSA bacteremia with a high burden of infections. However, the sites of infections are more important factors for the clinical outcome than the CIE.

The purpose of this study was to compare the clinical efficacy and safety of vancomycin to those of teicoplanin for the treatment of adult patients with health care-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) bacteremia. A multicenter observational study was prospectively conducted in 15 teaching hospitals in Korea between February 2010 and July 2011. Adult patients (≥18 years old) with HA-MRSA bacteremia who were initially treated with vancomycin (VAN) (n = 134) or teicoplanin (TEC) (n = 56) were enrolled. Clinical and microbiological responses and drug-related adverse events were compared between the two treatment groups using univariate and multivariate logistic regression analyses. The vancomycin and teicoplanin MICs were determined by Etest. The MRSA-related mortality, duration of fever, and duration of MRSA bacteremia in the treatment groups were not significantly different. There was no significant difference in the occurrence of drug-related adverse events. Among the 190 MRSA isolates, the VAN MICs ranged from 0.5 to 2 μg/ml (MIC50 and MIC90, 1.5 μg/ml), and the TEC MIC ranged from 0.5 to 8 μg/ml (MIC50, 3 μg/ml; MIC90, 6 μg/ml). In multivariate analyses, the antibiotic type (vancomycin or teicoplanin) was not associated with treatment outcomes. This study indicates that teicoplanin is an effective and safe alternative to vancomycin for the treatment of HA-MRSA bacteremia.

Background: Tigecycline has broad spectrum antimicrobial activity and is approved for complicated intra-abdominal infections, complicated skin and soft tissue infections, and community-acquired pneumonia. There are few data on clinical experience of tigecycline in hospital-acquired pneumonia (HAP) and Acinetobacter spp. infection., Methods: A retrospective study was performed at eight hospitals in Korea from May 2009 to January 2010. Adult patients treated with tigecycline regardless of their source of infection or pathogens were enrolled., Results: Tigecycline was administered in 108 patients. Pneumonia was the most common infection (43.5%), followed by skin and soft tissue infections (20.4%). Acinetobacter baumannii was isolated from 83 patients (76.9%) accounting for 50.3% of isolated pathogens, showing a resistance rate of 67.5% to carbapenems. Superinfection was identified in 32 patients (29.6%). Pseudomonas aeruginosa was most common microorganism causing superinfection (46.9%). Overall 30-day mortality rate was 52.9%. Thirty-day mortality rate of HAP and Acinetobacter spp. infection was 60.5% and 59.4%, respectively., Conclusion: Tigecycline can be considered as an alternative therapy in patients with HAP or infections caused by Acinetobacter spp., especially extensively drug-resistant A. baumannii.

Background/aims: Frequent pathogens of nosocomial meningitis were investigated and the adequacy of empiric antibiotic therapy was assessed. Outcomes of nosocomial meningitis were also evaluated., Methods: Ninety-one patients, who were diagnosed and treated for nosocomial meningitis at a single tertiary hospital in Daegu, Korea for 10 years, were included. Medical record and electronic laboratory data on the causative pathogens, antibiotics used, and outcomes were retrospectively investigated., Results: Coagulase-negative Staphylococcus (40.9%) was the most common pathogen, followed by Acinetobacter (32.5%). Both were cultured as a single organism in cerebrospinal fluid (CSF). Seventy-eight patients (85.7%) had infections related to external ventricular drains (EVD). The most common empirical antibiotics were extended-spectrum beta-lactam antibiotics plus vancomycin (35/91, 38.6%). Of the 27 patients who had cultured Acinetobacter in CSF, 10 (37%) were given the wrong empirical antibiotic treatment. Seven of the 27 patients (26.9%) with cultured Acinetobacter died, and overall mortality of the 91 patients was 16.5%. In the multivariate analysis, the presence of combined septic shock (p < 0.001) and a persistent EVD state (p = 0.021) were associated with a poor prognosis., Conclusions: Acinetobacter is one of the leading pathogens of nosocomial meningitis and may lead to inadequate coverage of empiric antibiotic therapy due to increasing resistance. An EVD should be removed early in cases of suspected nosocomial meningitis, and carbapenem might be required for the poor treatment response.

Objective: This study was conducted to identify the predictors of mortality and to evaluate the impact of methicillin resistance on outcome in patients with Staphylococcus aureus infection according to underlying conditions and type of infection., Methods: An observational cohort study including 4949 patients with S. aureus infection was conducted. We compared data from patients with MRSA infection with those with MSSA infection., Results: The 30-day mortality rate of MRSA group was significantly higher than that of MSSA group (15.6% vs. 6.2%, P < 0.001). However, MRSA infection was not found to be independent risk factor for mortality after adjusting for other variables (OR = 1.03, 95% CI = 0.80-1.32). When we analyzed patients with S. aureus bacteremia (n = 709), MRSA infection was found to be significantly associated with mortality in multivariate analysis (Adjusted OR = 1.69, 95% CI = 1.15-2.49). When the 30-day mortality rates were compared according to underlying diseases, the 30-day mortality rate of MRSA group was significantly higher than that of MSSA group in patients with malignancy or renal diseases. MRSA infection was also found to be one of the independent risk factors for mortality in patients with malignancy (adjusted OR = 1.69, 95% CI = 1.06-2.70) and in those with renal disease (adjusted OR = 1.70, 95% CI = 1.0-2.89), after adjustment for host variables., Conclusions: Methicillin resistance adversely affected the outcome of patients with S. aureus infection, in patients with cancer or renal disease and in those with S. aureus bacteremia, although MRSA infection was not found to be significantly associated with higher mortality in overall patient population., (Copyright © 2010 The British Infection Society. Published by Elsevier Ltd. All rights reserved.)

Objective: Ciprofloxacin-resistant Escherichia coli is growing concern in clinical settings. In this study, we investigated the distribution of virulence determinants and phylogenetic groups among community-onset, ciprofloxacin-resistant E. coli isolates causing urinary tract infections (UTIs) in Korea. In addition, the evidence of clonal spread in the community was also examined., Methods: From November 2006 to August 2007, 543 community-onset E. coli isolates causing UTIs were collected as part of a multicenter surveillance study. In vitro susceptibility testing was performed using broth microdilution method. Distribution of virulence determinants and phylogenetic groupings were examined. In addition, multilocus sequence typing (MLST) analysis was performed., Results: In vitro antimicrobial susceptibility testing revealed that 154 isolates (28.4%) were ciprofloxacin-resistant. Of these, 129 ciprofloxacin-resistant E. coli isolates were further characterized. As a result of phylogenetic subgrouping, we found that phylogenetic subgroup D was the most predominant (46 isolates, 35.7%), followed by B2 (44 isolates, 34.1%), A (21 isolates, 16.3%), and B1 (18 isolates, 14.0%). MLST analysis showed 48 sequence types (STs). The most prevalent ST was ST131 (32 isolates, 24.8%), followed by ST393 (23 isolates, 17.8%). While all ST131 isolates belonged to phylogenetic subgroup B2, which is known to be a highly virulent, all ST393 isolates belonged to subgroup D. ST131 and ST393 showed different profiles of virulence factors; papA, papG allele III, and traT genes were significantly more prevalent in ST131 than in ST393 (p values, <0.001)., Conclusions: Based on genotyping, it is suggested that epidemic and virulent ciprofloxacin-resistant E. coli clones such as ST131 and ST393 have disseminated in Korea. However, the diversity of CTX-M genes in ST131 isolates may indicate that ESBL genes have been acquired independently or several ESBL-producing, ciprofloxacin-resistant E. coli clones may have disseminated in the Korean community., (Copyright 2009 The British Infection Society. Published by Elsevier Ltd. All rights reserved.)

Background/aims: As bacterial resistance to antimicrobial agents has grown due to the increasing use of antimicrobial agents, we sought to evaluate the suitability of ceftriaxone usage (representative of third generation cephalosporins) at 10 university hospitals in Korea., Methods: We prospectively evaluated the appropriateness of antibiotic usage in 400 adult patients who received ceftriaxone between February 1, 2006 and June 30, 2006. Drug utilization evaluation (DUE) methods were based on standards set forth by the American Society of Hospital Pharmacists. The DUE criteria used in this study were modified to be more suitable in our hospital setting: justification of drug use, critical and process indications, complications, and outcome measures., Results: The average patient age was 64.4 years. The utilization of ceftriaxone was appropriate in 262 cases (65.5%) for the justification of use, while inappropriate use was observed in 138 cases (34.5%). Common reasons for inappropriate use of ceftriaxone included continued empiric use for presumed infections, prophylactic perioperative injection, and empiric therapy for fever. Most of the critical indications showed a high rate of suitability (66.5-98.5%). Complications occurred in 37 cases (9.3%). With respect to outcome measures, clinical responses were observed in 60.7% of cases, while only 15.7% of cases showed evidence of infection eradication via negative cultures., Conclusions: Appropriate use (65.5%) of ceftriaxone was higher than inappropriate use (34.5%) at university hospitals in Korea. Inappropriate utilization, however, including continued empiric use for presumed infections and prophylactic perioperative injection remained high. Intensification of educational programs and antibiotic control systems for ceftriaxone is needed to improve the suitability of antimicrobial use.

We investigated the characteristics of 48 carbapenem-resistant Acinetobacter baumannii isolates collected from 5 tertiary care hospitals in Korea by multilocus sequencing typing, pulsed-field gel electrophoresis, and polymerase chain reaction amplification of the antimicrobial resistance determinants. We identified 2 distinct main clones of carbapenem-resistant A. baumannii isolates, which showed different antimicrobial resistance profiles and are also differentiated by the kinds of oxacillinase (OXA) carbapenemases and Acinetobacter-derived cephalosporinase (ADC) beta-lactamases. One main clone, ST22:A, had 27 carbapenem-resistant isolates (56.3%), showed high polymyxin B and colistin resistances (33.3% and 37.0%, respectively), and contained both bla(OXA-51-like) and bla(OXA-23-like) genes and the bla(ADC-29) or bla(ADC-30) gene. In contrast, the other main clone, ST28:B, included 15 isolates (31.3%), showed complete susceptibilities to polymyxin B and colistin, and contained only the bla(OXA-51-like) gene and bla(ADC-31) or bla(ADC-32) genes. The distribution of these main carbapenem-resistant A. baumannii clones did not relate to locality, indicating that they are widespread in Korean hospitals. In addition, we found new types of PER beta-lactamases, PER-6.

This multinational study from Asia revealed that reduced susceptibility to ciprofloxacin (MIC, 0.125 to 1 microg/ml) in nontyphoid Salmonella isolates was common in Taiwan (48.1%) and Thailand (46.2%) and in S. enterica serotype Choleraesuis (68.8%) and S. Virchow (75.0%) from all countries. Reduced susceptibility to ceftriaxone (MIC, 2 to 8 microg/ml) remained uncommon in Asia, except in Taiwan (38.0%) or in S. Typhimurium (25.0%) from all countries.

Objectives: To investigate the impact of imipenem resistance on the mortality rate among patients with Acinetobacter bacteraemia., Methods: A retrospective, pairwise-matched (1:1), risk-adjusted (age, Pitt bacteraemia score) cohort study was performed at three tertiary care hospitals in Korea from January 2000 to June 2005., Results: Forty patients with imipenem non-susceptible Acinetobacter bacteraemia (INAB group) and 40 matched subjects (1:1 ratio) with imipenem-susceptible Acinetobacter bacteraemia (ISAB group) were included. Both groups had similar clinical features related to the severity of illness. The 30 day mortality rate was higher in the INAB group (57.5%) than the ISAB group (27.5%) (P = 0.007). The rate of discordant antimicrobial therapy was higher in the INAB group (65.0%) than the ISAB group (20.0%) (P < 0.001). The 30 day mortality rate was higher in the patients with discordant antimicrobial therapy (67.6%) than concordant antimicrobial therapy (23.9%) (P < 0.001). Multivariate analysis showed that age, the Pitt bacteraemia score, immunosuppressive status, and discordant antimicrobial therapy were independent risk factors for 30 day mortality among patients with Acinetobacter bacteraemia (P < 0.05). When discordant antimicrobial therapy was excluded in the multivariate analysis, the imipenem resistance was associated with 30 day mortality (P = 0.005)., Conclusions: Imipenem resistance has a significant impact on the mortality rate among patients with Acinetobacter bacteraemia, and this is mainly attributable to the higher rate of discordant antimicrobial therapy.

We tested the in vitro susceptibilities of 603 enterococcal isolates from eight tertiary-care hospitals in Korea. The quinupristin-dalfopristin resistance rate in Enterococcus faecium was very high (25 isolates, 10.0%). It was suggested that both clonal spread and the sporadic emergence of quinupristin-dalfopristin-resistant isolates may explain the high prevalence of quinupristin-dalfopristin resistance in Korea.

There have been conflicting data about the interactions between vancomycin and beta-lactam agents against Staphylococcus aureus strains with heterogeneous resistance to vancomycin. We evaluated the efficacy of these combinations against Mu 3 and heterogeneously vancomycin-resistant S. aureus (hetero-VRSA) strains which were isolated from Korean patients using a population analysis method. Antagonistic effects were observed when less than 1 g/mL of beta-lactam antibiotics was combined with vancomycin, whereas synergistic effects were noticed with more than 4 microgram/mL of beta-lactam antibiotics. The antagonistic effects at low concentrations of beta-lactams were most prominent at 2 microgram/mL of vancomycin, which were the vancomycin MICs of tested hetero-VRSA strains. This study showed the variable effects of vancomycin- beta-lactam combinations depending on the concentrations of beta-lactam antibiotics and this property could be used to develop screening methods for hetero-VRSA strains.

Stenotrophomonas maltophilia (previously named Xanthomonas maltophilia) is an aerobic, non-fermentive, Gram-negative bacillus that is wide spread in the environment. It was considered to be an organism with limited pathogenic potential, which was rarely capable of causing diseases in human other than those who were in debilitated or immunocompromised state. More recent studies have established that Stenotrophomonas maltophilia can behave as a true pathogen. Endocarditis due to this organism is rare, and only 24 cases of Stenotrophomonas maltophilia endocarditis have been reported in the medical literature. Most cases were associated with risk factors, including intravenous drug abuse, dental treatment, infected intravenous devices, and previous cardiac surgery. We present a case with two episodes of Stenotrophomonas maltophilia endocarditis after mitral valve prosthesis implantation, which was treated with antibiotics initially, and a combination of antibiotics and surgery later. To our knowledge, this is the first case of repetitive endocarditis due to Stenotrophomonas maltophilia.