Bok Kwon Lee

Chosun University, Goyang, Gyeonggi, South Korea

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Publications (21)45.26 Total impact

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    ABSTRACT: Paratyphoid fever is considered an emerging systemic intracellular infection caused by Salmonella enterica serotypes Paratyphi A, B, and C. We performed in vitro time-kill studies on three clinical isolates of nalidixic acid-resistant Salmonella serotype Paratyphi (NARSP) with different concentrations of ciprofloxacin and cefotaxime to identify combinations of antibiotics with synergistic activity against paratyphoid fever. Furthermore, we identify the frequency of mutations to ciprofloxacin, cefotaxime, and rifampin resistance and also sequenced the gyrA, gyrB, parC, and parE genes to identify the cause of resistance in NARSP. When the activity of ciprofloxacin at 0.75x MIC (0.012 to 0.38 microg/ml) with cefotaxime at the MIC (0.125 to 0.25 microg/ml) against all three NARSP isolates was investigated, synergy was observed at 24 h, and the bacterial counts were reduced by >3 log(10) CFU/ml. This synergy was elongated for up to 72 h in two out of three isolates. When ciprofloxacin at 0.75x MIC (0.012 to 0.38 microg/ml) was combined with cefotaxime at 2x MIC (0.25 to 0.50 microg/ml), synergy was prolonged for up to 72 h in all three isolates. Both Salmonella serotype Paratyphi A isolates carried single mutations in codon 83 of the gyrA gene and codon 84 of the parC gene that were responsible for their reduced susceptibility to ciprofloxacin, while no mutations were found in the gyrB or parE gene. The ciprofloxacin-plus-cefotaxime regimen was very effective in reducing the bacterial counts at 24 h for all three isolates, and this combination therapy may be helpful in reducing the chance of the emergence of fluoroquinolone-resistant mutants in patients with severe paratyphoid fever.
    Antimicrobial Agents and Chemotherapy 09/2010; 54(9):3696-701. · 4.57 Impact Factor
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    ABSTRACT: Typhoid fever is a systemic intracellular infection caused by Salmonellaenterica serotype Typhi. The emergence and spread of nalidixic acid-resistant S. Typhi (NARST) is challenging for clinicians in many countries owing to the lack of suitable treatment options. The aim of this study was to identify in vitro synergistic combinations of antibiotics against S. Typhi. In vitro time-kill studies were performed on three clinical NARST isolates and one type strain of nalidixic acid-susceptible S. Typhi (NASST) ATCC 9992 with ciprofloxacin, cefotaxime and azithromycin in various combinations. The combination of ciprofloxacin (0.012-0.375 microg/mL) and cefotaxime (0.063-0.125 microg/mL) against all three NARST strains and the NASST strain was significantly more effective in vitro in reducing bacterial counts by >or=3log(10) colony-forming units at 24h and showed synergistic effects. Combination therapy with ciprofloxacin and cefotaxime might be the treatment of choice for patients with typhoid fever. The combination of a fluoroquinolone and a beta-lactam, which are directed against different targets, may improve efficacy compared with a fluoroquinolone alone and may reduce the chance of fluoroquinolone-resistant mutants emerging in patients with severe typhoid fever.
    International journal of antimicrobial agents 08/2010; 36(2):155-8. · 3.03 Impact Factor
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    ABSTRACT: We subtyped 117 Vibrio vulnificus isolates from 85 V. vulnificus sepsis patients and 32 environmental samples by performing automated ribotyping for the purpose of molecular epidemiological study. Although there was one indistinguishable ribotype among the four human isolates and one environmental isolate, taken as a whole, the ribotypes were highly diverse regardless of sample sources. We report here for the first time the assorted ribotypes of V. vulnificus human and environmental isolates in Korea.
    Japanese journal of infectious diseases. 03/2010; 63(2):116-8.
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    ABSTRACT: Salmonella Enteritidis is the most common cause of salmonellosis in humans in South Korea. It has been recognized that the principal source of human infection with S. Enteritidis is chickens and their products such as meat and eggs. A total of 173 S. Enteritidis isolates from humans (65 isolates) and chickens or their products (108 isolates) were analyzed by antibiotic susceptibility assay, phage typing, and pulsed-field gel electrophoresis (PFGE). Drug resistance was found to streptomycin (32.3%), ampicillin (30.6%), nalidixic acid (30.1%), ticarcillin (30.1%), and tetracycline (28.3%). More than 70% of the isolates were found to be resistant to one or more antibiotics tested. The most frequent patterns of resistant isolates were resistance to nalidixic acid only (28.3%) and resistance to two antibiotics (four combinations; 20.2%). The most predominant phage type (PT) was PT1 (27.2%) followed by PT21 (20.8%) and PT4 (8.7%) in chicken and human isolates. Nineteen different PFGE patterns were found among the 173 isolates, and A1 was the most common PFGE pattern, followed by A6 (17.3%). Most S. Enteritis isolates (except two isolates with patterns B and C) showed similar PFGE patterns that differed by only a few bands. These results show that 2 or 3 subtypes of S. Enteritidis are shared to a large extent by humans and chickens. This implies the possibility of the spread of chicken S. Enteritidis to humans.
    Journal of Veterinary Medical Science 11/2009; 71(11):1433-8. · 0.88 Impact Factor
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    ABSTRACT: This study was designed to develop a multiplex PCR method with five specific primer pairs for the detection of Salmonella spp., Salmonella subspecies I, Salmonella enterica serovars Typhimurium, Typhi and Enteritidis. A multiplex PCR was constructed with five primer pairs for the detection of Salmonella and pathogenic Salmonella serovars, including a specific primer pair for Salmonella Typhi, based on the sequence comparison between genomic DNA sequences of 12 Salmonella strains. Each primer pair was specifically targeted to Salmonella spp., Salmonella subspecies I, Salmonella Typhimurium, Typhi and Enteritidis. This multiplex PCR was evaluated with various DNAs of Salmonella serovars that yielded high specificity for amplifying the expected PCR products of Salmonella serovars. Using this primer pair, a set of multiplex PCR was performed for the rapid identification of salmonellae and major pathogenic Salmonella serovars. Although this multiplex PCR method will need to be evaluated for a wide range of Salmonella serovars among multilaboratories, it should be useful for identifying clinically significant strains of Salmonella serovars rapidly and accurately without the need for serological testing.
    FEMS Microbiology Letters 10/2009; 301(1):137-46. · 2.05 Impact Factor
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    ABSTRACT: The multi-antimicrobial resistance gene cluster and its derivatives have been detected in Salmonella genomic island 1 (SGI1), which has been identified in the Salmonella enterica serovar Typhimurium, phage types DT104, DT12, DT120, and U302, as well as other Salmonella serovars, including Agona, Paratyphi B, Albany, Meleagridis, Newport, Cerro, Derby, Dusseldorf, Infantis, Kiambu, and Emek. We acquired 53 Salmonella Typhimurium DT104 isolates from diarrheal patients in Korea. From these isolates, we identified a novel antimicrobial resistance gene cluster as an additional gene cassette in SGI1 from a multi-antimicrobial resistant isolate. The minimum inhibitory concentration for this isolate against ampicillin and chloramphenicol was two to four times higher than those for other multi-antimicrobial-resistant Salmonella Typhimurium DT104 isolates. The new antimicrobial resistance gene cluster detected in this isolate consisted of bla(PSE-1), sul1 Delta, floR, and tetR, in that order. The order of this gene cluster was shuffled as compared to that of the known In104 in SGI1. This report is, to the best of our knowledge, the first to identify and describe an additional shuffled antimicrobial resistance gene cluster in SGI1.
    Foodborne Pathogens and Disease 04/2009; 6(4):471-9. · 2.28 Impact Factor
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    ABSTRACT: Salmonella enterica serovar Typhi is a Gram-negative bacterium causing the acute febrile disease typhoid fever. In Korea from 2004 to 2006, a total of 51 Salmonella Typhi isolates were identified in stool and blood from healthy carriers and patients with or without overseas travel histories. In this study, antibiogram, pulsed-field gel electrophoresis (PFGE), and automated ribotyping were performed as molecular epidemiological methods with phage typing as a classical subtyping tool of the isolates. Only two isolates were multidrug resistant and 82.3% of the isolates were susceptible to 16 antimicrobial agents tested. When the dendrogram was created based on the PFGE results, the subtypes could be clustered into five groups by 80% similarity criterion. The PFGE patterns of 31 isolates (60.8%) belonged to Cluster 3, the predominant cluster in the study. Three overseas travel-associated cases were differentiated into Cluster 4 of which three isolates were nalidixic acid or multidrug resistant. Major phage type and ribotype were A and PvuII-436-8-S-6, respectively. This study also showed the prevalence of PFGE Cluster 3 in Korea by clustering analysis and the link between some typhoid cases and travel to Cambodia, India, or Indonesia.
    Foodborne Pathogens and Disease 01/2009; 6(6):733-8. · 2.28 Impact Factor
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    ABSTRACT: Enterobacter sakazakii (E. sakazakii) infections are an important cause of life-threatening meningitis, septicemia, and necrotizing enterocolitis in infants. Dried infant formula milk is an important vehicle for E. sakazakii infection. E. sakazakii was isolated in Korea from dried infant formula milk. Although E. sakazakii infection of infants may occur in Korea, its prevalence has not yet been documented. Therefore, we determined the prevalence of E. sakazakii and documented symptoms. Between March and October 2006, 1,146 stool samples were collected from patients at Uijeongbu St. Mary's Hospital. Each fecal swab was dissolved in 10mL of buffered peptone solution, and enriched culture was streaked onto Druggan-Forsythe-Iversen (DFI) agar. Presumptive E. sakazakii colonies that exhibited a blue-green color during culture on DFI medium were selected. The identity of colonies that developed yellow pigment during culture on TSA was determined using the Vitek system and PCR. We isolated 4 E. sakazakii strains whose 16S rRNA sequence alignments had a similarity of 99% with those of 3 E. sakazakii ATCC strains. This is the first report on isolation of E. sakazakii from stool samples and to document the symptoms of Korean patients.
    Yonsei Medical Journal 01/2009; 49(6):1017-22. · 1.31 Impact Factor
  • Infection and Chemotherapy. 01/2009; 41(3).
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    ABSTRACT: Biofilm formation in association with the intercellular adhesion (icaADBC) gene cluster is a serious problem in nosocomial infections of Staphylococcus aureus. In all 112 S. aureus strains tested, the ica genes were present, and none of these strains formed biofilms. The biofilm formation is known to be changeable by environmental factors. We have found about 30% of phase variation in these strains with treatment of tetracycline, pristinamycin, and natrium chloride. However, this phenotype disappeared without these substances. Therefore, we have constructed stable biofilm-producing variants through a passage culture method. To explain the mechanism of this variation, nucleotide changes of ica genes were tested in strain S. aureus 483 and the biofilm-producing variants. No differences of DNA sequence in ica genes were found between the strains. Additionally, molecular analysis of three regulatory genes, the accessory gene regulator (agr) and the staphylococcal accessory regulator (sarA), and in addition, alternative transcription factor sigma B (sigB), was performed. The data of Northern blot and complementation showed that SigB plays an important role for this biofilm variation in S. aureus 483 and the biofilm-producing variants. Sequence analysis of the sigB operon indicated three point mutations in the rsbU gene, especially in the stop codon, and two point mutations in the rsbW gene. This study shows that this variation of biofilm formation in S. aureus is deduced by the role of sigB, not agr and sarA.
    Journal of Microbiology and Biotechnology 02/2008; 18(1):28-34. · 1.40 Impact Factor
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    ABSTRACT: The multilocus sequence typing scheme used previously for phylogenetic analysis of Escherichia coli was applied to 107 clinical isolates of Shigella flexneri. DNA sequencing of 3423 bp throughout seven housekeeping genes identified eight new allele types and ten new sequence types among the isolates. S. flexneri serotypes 1-5, X and Y were clustered together in a group containing many allelic variants while serotype 6 formed a distinct group, as previously established.
    Journal of Medical Microbiology 12/2007; 56(Pt 11):1460-6. · 2.30 Impact Factor
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    Japanese journal of infectious diseases 12/2007; 60(6):412-3. · 1.51 Impact Factor
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    ABSTRACT: Salmonella enterica subspecies enterica serovar Paratyphi B [O1,4,(5),12 : Hb : 1,2] can cause either an enteric fever (paratyphoid fever) or self-limiting gastroenteritis in humans. The d-tartrate non-fermenting variant S. enterica subsp. enterica serovar Paratyphi B dT- (S. Paratyphi B) is the causative agent of paratyphoid fever, and the d-tartrate fermenting variant S. enterica subsp. enterica serovar Paratyphi B dT+ (S. Paratyphi B dT+; formerly called Salmonella Java) causes gastroenteritis. S. Java is currently recognized as an emerging problem worldwide. Twelve dT+ S. Java isolates were collected in Indonesia between 2000 and 2002. One-third of them contained Salmonella genomic island 1 (SGI1), which gives the multidrug-resistant phenotype to the bacteria. In this study, a PCR-based method to detect a single nucleotide difference responsible for the inability to ferment d-tartrate, reported elsewhere, was validated. The d-tartrate fermenting phenotype of S. Java was converted to the non-fermenting phenotype by the disruption of the ORF STM 3356, and the d-tartrate non-fermenting phenotype of the ORF STM 3356-disrupted strain and the dT- reference strain was changed to the dT+ phenotype by complementing ORF STM 3356 in trans. The results show that the dT+ phenotype requires a functional product encoded by STM 3356, and support the use of the PCR-based discrimination method for S. Paratyphi B and S. Java as the standard differentiation method.
    Journal of Medical Microbiology 01/2007; 55(Pt 12):1661-5. · 2.30 Impact Factor
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    ABSTRACT: We investigated the trends of nalidixic acid resistance in human non-typhoid Salmonella enterica in a Korean population, and examined some possible mechanisms involved in this resistance. A total of 261 clinical strains were tested. For all strains, the MICs of nalidixic acid were determined. Nalidixic acid-resistant strains underwent further analysis, including determination of MICs of other antibiotics, mutation analysis within the topoisomerase genes, organic solvent tolerance test, western blotting for AcrA, marOR mutation analysis, ciprofloxacin accumulation test, and PCR for the qnr gene. The clonal relationships of Salmonella strains were examined by random amplified polymorphic DNA analysis. The incidence of nalidixic acid resistance increased from 1.8% in 1995-96 to 21.8% in 2000-02. The resistance rate was higher in S. enterica serotype Enteritidis (21.6%) than in serotype Typhimurium (12.1%). The nalidixic acid resistance rates in Salmonella Enteritidis varied according to the phage type (PT) and Salmonella Enteritidis PT 1 was most commonly associated with resistance to nalidixic acid. Several cases of clonal spread, especially by Salmonella Enteritidis PT 1, were identified. Of the 46 nalidixic acid-resistant strains, 43 had single mutations in the gyrA gene. Four strains were organic solvent-tolerant and were associated with decreased ciprofloxacin accumulation; three of these showed increased expression of AcrA and had novel mutations in marOR (84L). The qnr gene was not identified. Recently, the rate of nalidixic acid resistance in Korean clinical Salmonella strains markedly increased and it was partly due to the clonal spread of Salmonella Enteritidis, especially PT 1. The main mechanism of nalidixic acid resistance was a mutation in the gyrA region.
    Journal of Antimicrobial Chemotherapy 01/2006; 56(6):1111-4. · 5.34 Impact Factor
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    ABSTRACT: A chloramphenicol-resistant strain of Salmonella enterica serovar Typhi was first noted in Korea in 1992, when a resistant isolate was detected in a returned traveler. Continued isolation of multidrug-resistant (MDR) strains thereafter in other settings prompted a retrospective analysis of laboratory records and phenotypic and genotypic analyses of 12 chloramphenicol-resistant isolates. Among these, one isolate was resistant only to chloramphenicol, and the other isolates were also resistant to ampicillin and co-trimoxazole. MDR was transferred by conjugation from 9 of the 11 isolates. PCR showed that all isolates had an incompatible group HI1 plasmid, and oriT was detected in 10 isolates, which included strains with an unsuccessful transfer of resistance. All of the ampicillin-resistant isolates had a beta-lactamase band of pI 5.4 and bla(TEM) alleles. A PCR amplicon from an isolate showed that the sequences were identical to those of bla(TEM-1), suggesting that all isolates had a TEM-1 beta-lactamase. All isolates had class 1 integrons: 10 isolates had integrons of ca. 1.2 kb with dhfr7 gene cassettes, and 1 isolate had an integron of ca. 2.3 kb with aacA4 and bla(OXA-1)-like gene cassettes. The pulsed-field gel electrophoresis patterns of 7 of 11 MDR isolates were identical and indistinguishable from those reported for isolates in India and Indonesia. In conclusion, some of the MDR strains in Korea are related to those in other Asian countries. Susceptibility testing became necessary for selection of antimicrobial agents for the optimal treatment of patients with the emergence of MDR Salmonella serovar Typhi in Korea.
    Antimicrobial Agents and Chemotherapy 12/2004; 48(11):4130-5. · 4.57 Impact Factor
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    ABSTRACT: Salmonella enterica serovar Typhimurium DT104 (Salmonella Typhimurium DT104 or DT104) has been emerging as a common pathogen for human in Korea since 1997. In order to compare the genomic relationship and to search for the dominant strains in Korea, we conducted pulsed-field gel electrophoresis (PFGE) and IS200 fingerprinting of 25 epidemiological unrelated isolates from human and animals from Korea and cattle from America. Two Salmonella Typhimurium DT104 isolates from human in Korea and all 8 isolates from American cattle had indistinguishable patterns from the PFGE and IS200 fingerprinting but multidrug-resistant Salmonella Typhimurium isolates, including DT104, from Korean animals had diverse genetic patterns. The data suggest that a dominant DT104 strain might have circulated between Korean and American cattle and that it had a high level of clonality.
    The Journal of Microbiology 04/2004; 42(1):14-9. · 1.28 Impact Factor
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    ABSTRACT: The aim of this study is to characterize the epidemiological features of typhoid fever, categorized as class 1 notifiable disease in Korea and to analyze the recent change of antimicrobial resistance of Salmonella enterica serotype Typhi isolated nationwide. We retrospectively analyzed the 1,692 culture-proven cases from 1992 to 2000, using the data of the Korean National Institute of Health. The overall incidence of culture-proven typhoid fever was 0.41 per 100,000 population. It occurred all over the country, but the southeastern part of Korean peninsula had the higher incidence rate than other areas. There were several outbreaks suspected, of which two outbreaks were confirmed. The resistance rate against chloramphenicol showed mild increase, but the ampicillin, trimethoprim/sulfamethoxazole, kanamycin, or nalidixic acid resistance remained at the similar levels for the past 9 yr. There were 21 (1.3%) multidrug-resistant (MDR) strains isolated since 1992, and the number of those has increased. Two strains resistant to ciprofloxacin were first identified in Korea.
    Journal of Korean Medical Science 03/2004; 19(1):15-20. · 1.25 Impact Factor
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    ABSTRACT: A total of 74 isolates of Salmonella enterica serovar London were collected through the Laboratory-Based Diarrheal Diseases Surveillance in 2000-2001. In order to characterize the isolates and investigate the source of the epidemic, we performed antimicrobial susceptibility tests and XbaI Pulsed-field gel electrophoresis (PFGE) of 44 Salmonella London isolates. Forty isolates were from feces of infants and four isolates were from adults aged 30, 52, 54, and 59 yr. Two subtypes were identified: a tetracycline-susceptible A 0 PFGE pattern and a tetracyclineresistant A 1 PFGE pattern. Interestingly, the isolates from all infants and one 30-yr-old adult were A 0 PFGE pattern and tetracycline-susceptible. Furthermore, the A 0 PFGE pattern strain was approximately 2 times more virulent than the A 1 PFGE pattern strain, according to the results of in vitro invasion assay using J774A.1 macrophage-like cells. These results indicate that the active surveillance with molecular epidemiological tools would be valuable for promptly finding new epidemic strains. Our results also suggested that the virulent Salmonella London strain might infect the infants through a common contaminated source.
    Journal of Korean Medical Science 07/2003; 18(3):325-30. · 1.25 Impact Factor
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    ABSTRACT: Six strains of Salmonella enterica serovar Typhi which were resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, streptomycin, tetracycline, and gentamicin were isolated in Korea. This multidrug resistance was transferred by a conjugative plasmid of about 50 kb. The plasmid harbored a class 1 integron, which included six resistance genes, aacA4b, catB8, aadA1, dfrA1, aac(6')-IIa, and the novel blaP2, in that order. All of the isolates showed the same-size plasmids and the same ribotyping patterns, which suggests a clonal spread of these multidrug-resistant isolates.
    Antimicrobial Agents and Chemotherapy 07/2003; 47(6):2006-8. · 4.57 Impact Factor
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    ABSTRACT: Fourteen and 22 each of Salmonella Enteritidis and Salmonella Typhimurium (S. Typhimurium) were isolated from animals from 1983 to 1999 in Korea and tested for their antibiotic resistance patterns, phage types and resistance gene patterns. S. Typhimurium isolates were highly resistant to streptomycin, sulfisoxazole and tetracycline, 95, 95 and 86%, respectively. The incidence of multiple antibiotic resistance (resistant to more than two drugs tested) of S. Typhimurium isolates was extremely high (100%) comparing to S. Enteritidis isolates (21%). Two of the five ACSSuT (ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline) resistant type S. Typhimurium isolates were phage type definitive type 104 (DT104). For the detection of resistance related genes in S. Enteritidis and S. Typhimurium isolates, particularly ACSSuT type S. Typhimurium, antibiotic resistance genes, cmlA/tetR, bla(PSE-1) and bla(TEM), and genus Salmonella specific gene, sipB/C, were amplified using four pairs of primers in a hot-start multiplex polymerase chain reaction (PCR). Two Korean isolates of S. Typhimurium DT104 showed bla(TEM) amplicons instead of bla(PSE-1) for the ampicillin resistance and they were susceptible to florfenicol. The multiplex PCR used in this study was useful in characterization of multiple drug resistant Salmonella isolates, especially ACSSuT type S. Typhimurium, and identification of beta-lactamase gene distribution among Salmonella isolates.
    Veterinary Microbiology 06/2002; 86(4):295-301. · 3.13 Impact Factor

Publication Stats

201 Citations
45.26 Total Impact Points

Institutions

  • 2010
    • Chosun University
      • Department of Medicine
      Goyang, Gyeonggi, South Korea
  • 2007–2010
    • National Institute of Health, Korea
      • Division of Enteric Bacterial Infections
      Cheongsong gun, North Gyeongsang, South Korea
  • 2006
    • Korea Centers for Disease Control and Prevention
      Daiden, Daejeon, South Korea
  • 2004
    • Inje University Paik Hospital
      • Department of Family Medicine
      Goyang, Gyeonggi, South Korea