CTX-M-55-Type Extended-Spectrum beta-lactamase-Producing Shigella sonnei Isolated from a Korean Patient Who Had Travelled to China

We report a case of CTX-M-55-type extended-spectrum beta-lactamase (ESBL)-producing Shigella sonnei infection in a 27-year-old Korean woman who had traveled to China. The patient was admitted to the hospital due to abdominal pain, watery diarrhea, and fever (39.3degrees C). S. sonnei was isolated from her stool specimens, and the pathogen was found to be resistant to cefotaxime due to CTX-M-55-type ESBL. Insertion sequence (IS)Ecp1 was found upstream of the blaCTX-M-55 gene. The blaCTX-M-55 gene was transferred from the S. sonnei isolate to an Escherichia coli J53 recipient by conjugation. Pulsed-field gel electrophoresis and Southern blotting revealed that the blaCTX-M-55 gene was located on a plasmid of approximately 130 kb.

Loss of blaVIM-2 and blaIMP-1 during the Storage of Gram-Negative Bacilli, Antimicrobial Susceptibility of the Gene-Lost Strain, and Location of the Gene in the Cell / 대한임상미생물학회지

BACKGROUND: Gram-negative bacilli can be stored in cystine tryptic agar (CTA) at room temperature for over 1 year, but we experienced a loss of imipenem resistance among VIM-2-producing isolates. The aims of this study were to determine the frequency of loss of IMP-1 and VIM-2 genes during storage in CTA at room temperature and to document any change in the MIC of antimicrobial agents and the location of the gene. METHODS: Bacteria were isolated from clinical specimens at Severance Hospital collected from 1995-2000. Modified Hodge and double disk synergy tests were performed for screening of MBL-production isolates, and blaIMP-1 and blaVIM-2 were detected by PCR. Loss of resistance was tested in CTA at room temperature. PFGE and hybridization using a blaVIM-2 probe were carried out to determine the location of the VIM-2 gene. RESULTS: When VIM-2- and IMP-1-producing strains of eight P. aeruginosa and two Acinetobacter spp. were stored in CTA at room temperature, some isolates lost imipenem resistance after 3 days and 90% lost resistance after 15 weeks. Loss of resistance genes resulted in a decrease of the MIC of imipenem from 32-128 mug/mL to 0.5-8 mug/mL for P. aeruginosa, and from 32 mug/mL to 0.25-4 mug/mL for Acinetobacter spp. Hybridization of I-CeuI and S1-digested and PFGE suggested that VIM-2 genes are located on approximately 50-100 kb or 400 kb plasmids. CONCLUSION: Isolates may lose resistance genes when stored in CTA at room temperature. Therefore, it is necessary for MBL-production tests including the Modified Hodge test and double disk synergy test and detection of MBL genes.

Molecular and Phenotypic Characteristics of 16S rRNA Methylase-producing Gram-negative Bacilli / 대한임상미생물학회지

BACKGROUND: Recently a novel plasmid-mediated resistant mechanism that conferred high-level resistance to aminoglycoside via methylation of 16S rRNA was reported. The aims of this study were to determine the prevalence of the 16S rRNA methylase genes and to characterize the coresistance to other antibiotics in Gram-negative bacilli. METHODS: Consecutive non-duplicate Gram-negative bacilli were isolated from clinical specimens at a Korean secondary- and tertiary-care hospital from July 2006 to June 2007. The antimicrobial susceptibility was tested by the CLSI agar dilution method,and PCR was performed to detect the 16S rRNA methylase genes in the arbekacin-resistant isolates. RESULTS: In Gram-negative bacilli, the proportions of 16S rRNA methylase gene-positive isolates were 5% (75/1,471) in the secondary-carehospital and 4% (48/1,251) in the tertiary-care hospital, and the positive rates by species were 1% Escherichiae coli 16% (10/1,062), Klebsiella pneumoniae 16% (75/460), K. oxytoca 2% (1/44), Citrobacter spp. 9% (7/82), Enterobacter spp. 2% (4/181), Serratia marcescens 6% (6/100), Proteus miriabilis 4% (2/57), Achromobacter xylosoxidans 20% (1/5), Pseudomonas aeruginosa < 1% (1/505), Acinetobacter spp. 10% (11/112), and Stenotrophomonas maltophilia 2% (1/66), respectively. Among 16S rRNA methylase-positive isolates from secondary- and tertiary-care hospitals, 93% (70/75) and 90% (43/48), respectively, were armA positive, and others, except one rmtA positive isolate, were positive for the rmtB gene, according to PCR results. The rates of ESBL-positive and cefoxitin-resistant K. pneumoniae were 59% and 92%,s respectively. In addition, 91% of 16S rRNA methylase-producing K. pneumoniae were positive for qnrB. There were no MBL producers among 16S rRNA methylase-producing Pseudomonas and Acinetobacter species. CONCLUSION: The novel aminoglycoside-resistant mechanisms involving16S rRNA methylase were prevalent and widely distributed among Gram-negative bacilli in Korea, and other resistance mechanisms were commonly associated with 16S rRNA methylase-mediated resistance in Korea.

Carbapenem Resistance Mechanisms and Molecular Epidemiology of Acinetobacter spp. from Four Hospitals in Seoul and Gyeonggi Province in 2006 / 대한임상미생물학회지

BACKGROUND: Increasing numbers of Acinetobacter spp. resistant to multiple drugs, including carbapenem, has been a serious problem. The aims of this study were to determine carbapenem resistance patterns and mechanisms, as well as to study the molecular epidemiology of Acinetobacter spp. METHODS: Clinical isolates of Acinetobacter spp. were collected from May to November in 2006. Antimicrobial susceptibility testing was performed using CLSI disk diffusion and agar dilution methods. Metallo-beta-lactamase- and OXA carbapenemase-producing isolates were detected by PCR. Carbapenem resistance and hydrolytic activities were compared according to OXA type and presence of ISAba1. Pulsed-field gel electrophoresis (PFGE) was performed to determine the epidemiologic features. RESULTS: The imipenem non-susceptible rates were variable from 10% to 67%. Among 151 isolates carrying bla(OXA-51-like), 75 isolates carried both bla(OXA-51-like) and ISAba1, and 25 isolates had both bla(OXA-51-like), bla(OXA-23-like), and ISAba1. Carbapenem MICs of both bla(OXA-51-like) and ISAba1-carrying isolates were higher than those with bla(OXA-51-like) only. Carbapenem MICs of bla(OXA-23-like)-carrying isolates were higher than those with both bla(OXA-51-like) and ISAba1. Both bla(OXA-51-like) and ISAba1-carrying isolates and blaOXA-51-like, blaOXA-23-like, and ISAba1-carrying isolates demonstrated higher hydrolysis activities in oxacillin and carbapenems. Most of the tested isolates were susceptible to tigecycline, and all of them were susceptible to colistin. Pulsed-field gel electrophoresis suggested that there had been several outbreaks of bla(OXA-23-like) and bla(OXA-51-like)-positive strains. CONCLUSION: Carbapenem non-susceptible Acinetobacter isolates and OXA carbapenemase-producing isolates were prevalent. Dissemination of bla(OXA)-harboring isolates may make it difficult to treat infections due to carbapenem-resistant Acinetobacter spp. Further surveillance studies are required to prevent the spread of carbapenem resistance.

Identification of Bacterial and Fungal Isolates by Sequence Analysis of 16S rRNA and Internal Transcribed Spacer / 대한임상미생물학회지

BACKGROUND: Accurate and rapid identification of pathogens is one of the most important tasks of the clinical microbiology laboratory, and, in cases of rare pathogens, the identification is difficult and time-consuming upon the use of conventional methods alone. Herein, we will report our molecular work involving the identification of bacteria and fungi. METHODS: Sixty bacterial isolates had been collected from November 2004 to May 2007, and 15 fungal isolates had been collected from September 2005 to May 2007. Species identifications were performed using sequence analyses of the 16S rRNA region of bacteria and the internal transcribed spacer (ITS) region of fungi. The data were compared with those of GenBank (http://www.ncbi.nlm.nih.gov/) or EMBL (http://www.ebi.ac.uk/embl/). RESULTS: Sixty bacterial isolates included: 23 isolates with genus information (group 1), 17 isolates (group 2) that were too fastidious for genus or species identification, 16 isolates (group 3) with results from identification kits having low confidence, and 4 isolates (group 4) with odd antibiograms according to the species. In 58 of 60 isolates, identification of the genus or species could be obtained using molecular genetic methods. Thirty-eight isolates (63%) and 20 (33%) of 58 isolates could be identified at the species and genus levels, repectively. Among the total of 15 fungal isolates, 11 (73%) and 4 (27%) isolates were identified at the species and genus levels, respectively. CONCLUSION: 16S rRNA and ITS sequencing analyses are very useful for identifying the species or genus of a pathogenic microorganism in the clinical microbiology laboratory.

In vitro Activities of Mecillinam Against Clinical Isolates of Enterobacteriaceae

BACKGROUND: Mecillinam, an amidinopenicillin antibiotic, has been used to treat urinary tract infections and bacterial enteritis in many countries. In this study, we evaluated in vitro activity of mecillinam against Enterobacteriaceae isolates from urine, and Salmonella and Shigella isolates from patients with bacterial gastroenteritis. MATERIALS AND METHODS: A total of 308 clinical strains were collected and were comprised of Escherichia coli (n=109), Klebsiella pneumoniae (n=52), Enterobacter spp. (n=30), Serratia marcescens (n=30) and Proteus spp. (n=29) isolated from a university hospital in Korea in 2007, and of Salmonella spp. (n=28) and Shigella spp. (n=30) isolated from Korean diarrheal patients from 2001 to 2006. Antimicrobial susceptibility was tested by Clinical Laboratory Standard Institute (CLSI) agar dilution method. CLSI breakpoint of mecillinam for E. coli urinary tract isolates was applied to all other isolates. RESULTS: In E. coli, rate of susceptibility to ampicillin was 30%, but 99-100% to amikacin and cefotaxime. Most (96%) of E. coli isolates, including extended-spectrum beta-lactamase (ESBL) producers, were susceptible to mecillinam. All ESBL producers, except for one isolate, were inhibited by 128 microg/mL and most of them were resistant to mecillinam. All Salmonella isolates and 27 of 30 Shigella isolates were susceptible to mecillinam. CONCLUSION: Mecillinam was active in vitro against most Enterobacteriaceae, Salmonella, and Shigella isolates except for S. marcescens. Therefore, mecillinam can be a good alternative agent for treating urinary tract infection and bacterial gastroenteritis.

In vitro Activities of Mecillinam Against Clinical Isolates of Enterobacteriaceae

BACKGROUND: Mecillinam, an amidinopenicillin antibiotic, has been used to treat urinary tract infections and bacterial enteritis in many countries. In this study, we evaluated in vitro activity of mecillinam against Enterobacteriaceae isolates from urine, and Salmonella and Shigella isolates from patients with bacterial gastroenteritis. MATERIALS AND METHODS: A total of 308 clinical strains were collected and were comprised of Escherichia coli (n=109), Klebsiella pneumoniae (n=52), Enterobacter spp. (n=30), Serratia marcescens (n=30) and Proteus spp. (n=29) isolated from a university hospital in Korea in 2007, and of Salmonella spp. (n=28) and Shigella spp. (n=30) isolated from Korean diarrheal patients from 2001 to 2006. Antimicrobial susceptibility was tested by Clinical Laboratory Standard Institute (CLSI) agar dilution method. CLSI breakpoint of mecillinam for E. coli urinary tract isolates was applied to all other isolates. RESULTS: In E. coli, rate of susceptibility to ampicillin was 30%, but 99-100% to amikacin and cefotaxime. Most (96%) of E. coli isolates, including extended-spectrum beta-lactamase (ESBL) producers, were susceptible to mecillinam. All ESBL producers, except for one isolate, were inhibited by 128 microg/mL and most of them were resistant to mecillinam. All Salmonella isolates and 27 of 30 Shigella isolates were susceptible to mecillinam. CONCLUSION: Mecillinam was active in vitro against most Enterobacteriaceae, Salmonella, and Shigella isolates except for S. marcescens. Therefore, mecillinam can be a good alternative agent for treating urinary tract infection and bacterial gastroenteritis.

Resistance Trends of Bacteroides fragilis Group Over an 8-Year Period, 1997-2004, in Korea / 대한진단검사의학회지

BACKGROUND: Bacteroides fragilis group organisms are the most frequently isolated anaerobes in human infections. Increasing resistance to various antimicrobial agents is a significant problem in choosing appropriate antimicrobial agents to treat anaerobic infections. Periodic monitoring of the regional resistance trends of B. fragilis group isolates is needed. METHODS: A total of 466 nonduplicate clinical isolates of B. fragilis group organisms (276 B. fragilis, 106 Bacteroides thetaiotaomicron, and 84 other B. fragilis group organisms) were collected during the 8-yr period from 1997 to 2004 in a Korean university hospital. Minimum inhibitory concentrations to various antimicrobial agents were determined by the CLSI agar dilution method. RESULTS: Eight isolates were resistant to imipenem. Additionally, the resistance rates to cefotetan were decreased in B. thetaiotaomicron, while those for clindamycin were significantly increased compared to the rates found in previous studies. Depending on species, resistance rates were 1-4% for imipenem, 1-6% for piperacillin-tazobactam, 4-11% for cefoxitin, 33-49% for piperacillin, 14-60% for cefotetan, and 51-76% for clindamycin. No isolates were resistant to chloramphenicol or metronidazole. CONCLUSIONS: Piperacillin-tazobactam, cefoxitin, imipenem, chloramphenicol, and metronidazole are still active against B. fragilis group isolates, while clindamycin no longer has a value as an empirical therapeutic agent in Korea. Furthermore, this study identified the first imipenem-resistant B. fragilis group isolates in Korea.

Detection of CTX-M-Type Extended-Spectrum beta-Lactamase in Clinical Isolates of Chromosomal AmpC beta-Lactamase-Producing Enterobacteriaceae from Korea and Their Molecular Characteristics / 대한임상미생물학회지

BACKGROUND: Clinical isolates of AmpC beta-lactamase- producing Enterobacteriaceae were evaluated to determine the prevalence of CTX-M extended-spectrum beta-lactamases (ESBLs) and their genetic environments. METHODS: A total of 250 non-duplicate isolates of Eneterobacter aerogenes, E. cloacae, Citrobacter freundii, Serratia marcescens and Morganella morganii were collected at a Korean hospital. ESBL production was determined by double disk synergy test. For ESBL producers, bla genes were sequenced and blaCTX-M environment was characterized by PCR mapping and sequencing. RESULTS: Among the 250 isolates 29 (11.6%) produced ESBL, and 14 of the 29 isolates produced CTX-M ESBLs, including CTX-M-9 by 8 isolates, CTX-M-3 by 4 isolates, CTX-M-12 by 1 isolate, and CTX-M-14 by 1 isolate. ISEcp1 was present upstream of blaCTX-M-3, 12, and 14. Three of the four CTX- M-3 producers had the same genetic environment (pemK-ISEcp1-blaCTX-M-3-orf477-mucA). An IS903-like element was found downstream of blaCTX-M-14. ISCR1 was identified upstream of blaCTX-M-9 and ISCR1 and blaCTX-M-9 were located on sul1-type class 1 integron. The variable region between the 5'-CS and the first 3'-CS contained dfrA16 and aadA2. Its structure was similar to that of In60, but our isolates did not have IS3000 or second 3'-CS. CONCLUSION: CXT-M type ESBL was prevalent in AmpC beta-lactamase-producing Enterobacteriaceae, particularly E. cloacae. blaCTX-M genes were associated with ISEcp1 or ISCR1. This is the first report on the genetic environment of blaCTX-M in Korean isolates.

In Vitro Activity of Arbekacin Against Clinical Isolates of Staphylococcus species and Gram-negative Bacilli / 대한진단검사의학회지

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) and some gram-negative bacilli are very prevalent nosocomial pathogens, commonly causing mixed infections, and are often resistant to multiple drugs. Arbekacin is an aminoglycoside used for the treatment of MRSA infections, but is also active against some gram-negative bacilli. The aim of this study was to determine in vitro activity of arbekacin against recent clinical isolates of staphylococci and gram-negative bacilli. Materials and METHODS: The strains were isolated from clinical specimens of patients at Severance Hospital in 2003. Antimicrobial susceptibility was tested by the Clinical and Laboratory Standards Institute agar dilution method. The following arbekacin breakpoints were used: susceptible, or =16 microgram/mL . RESULTS: All isolates of staphylococci tested were inhibited by 32-fold and >32-128-fold lower than those of amikacin and gentamicin, respectively. The resistance rates of MRSA, methicillin-susceptible S. aureus, methicillin-resistant coagulase-negative staphylococci (CNS) and methicillin-susceptible CNS were 0% to arbekacin, 0-54% to amikacin, and 24-79% to gentamicin. The MIC90s of arbekacin for Escherichia coli and Citrobacter freundii, 1 microgram/mL and 16 microgram/mL, were 2-4-fold and 8-16-fold lower than those of amikacin and gentamicin, respectively. However, The MIC90s of arbekacin for other species of gram-negative bacilli, 64->128 microgram/mL, were similar to those of other aminoglycosides. CONCLUSIONS: Arbekacin may be a useful alternative to glycopeptides for the treatment of monomicrobial methicillin-resistant staphylococcal infections, as well as mixed infections with gram-negative bacilli, as most isolates of E. coli, C. freundii and some other gram-negative bacilli were also susceptible to arbekacin.

In Vitro Activity of Arbekacin Against Clinical Isolates of Staphylococcus species and Gram-negative Bacilli / 대한진단검사의학회지

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) and some gram-negative bacilli are very prevalent nosocomial pathogens, commonly causing mixed infections, and are often resistant to multiple drugs. Arbekacin is an aminoglycoside used for the treatment of MRSA infections, but is also active against some gram-negative bacilli. The aim of this study was to determine in vitro activity of arbekacin against recent clinical isolates of staphylococci and gram-negative bacilli. Materials and METHODS: The strains were isolated from clinical specimens of patients at Severance Hospital in 2003. Antimicrobial susceptibility was tested by the Clinical and Laboratory Standards Institute agar dilution method. The following arbekacin breakpoints were used: susceptible, or =16 microgram/mL . RESULTS: All isolates of staphylococci tested were inhibited by 32-fold and >32-128-fold lower than those of amikacin and gentamicin, respectively. The resistance rates of MRSA, methicillin-susceptible S. aureus, methicillin-resistant coagulase-negative staphylococci (CNS) and methicillin-susceptible CNS were 0% to arbekacin, 0-54% to amikacin, and 24-79% to gentamicin. The MIC90s of arbekacin for Escherichia coli and Citrobacter freundii, 1 microgram/mL and 16 microgram/mL, were 2-4-fold and 8-16-fold lower than those of amikacin and gentamicin, respectively. However, The MIC90s of arbekacin for other species of gram-negative bacilli, 64->128 microgram/mL, were similar to those of other aminoglycosides. CONCLUSIONS: Arbekacin may be a useful alternative to glycopeptides for the treatment of monomicrobial methicillin-resistant staphylococcal infections, as well as mixed infections with gram-negative bacilli, as most isolates of E. coli, C. freundii and some other gram-negative bacilli were also susceptible to arbekacin.

Comparison of Tn1546-like Elements in vanA Genotype Enterococcus gallinarum and E. faecalis or E. faecium / 대한임상미생물학회지

BACKGROUND: Enterococcus gallinarum, an organism often found in the intestine, is intrinsically resistant to low level vancomycin, but some of them are highly resistant to vancomycin due to acquisition of vanA gene. We occasionally detected both vanA carrying E. gallinarum and E. faecalis or E. faecium in the same patients, suggesting transfer of the resistance gene from the latter. In this study, the structures of Tn1546-like elements in E. gallinarum, and E. faecalis or E. faecium from the same patients were compared to determine the clinical significance of the vanA genotype E. gallinarum isolates. METHODS: Six pairs of vanA genotype E. gallinarum and E. faecalis or E. faecium were isolated at a tertiary- care hospital in Korea during 2000 to 2004. Species identification was performed by conventional methods. and the vancomycin-resistance genotypes were determined by PCR. For structural analysis of Tn1546-like elements, overlapping PCR amplification and sequencing of the internal regions were performed. RESULTS: All isolates were positive for vanA genes by PCR. The analysis of Tn1546-like elements showed structurally related three types of distribution of IS elements integrated: Type I had insertion of an IS1542 in the orf2-vanR intergenic region, and an IS1216V in the vanX-vanY intergenic region. Type II was similar with Type I but accompanied with the partial and complete deletions of orf1 and orf2. Type III had an IS1216V and an IS1542 in the orf2-vanR intergenic region, and an IS1216V in the vanX-vanY intergenic region. Two of the six vanA clusters in E. gallinarum isolates had structures identical to those in E. faecalis or E. faecium strains isolated from the same patients. However, in some isolate pairs, the origin of Tn1546 cannot be determined, because the structures were not identical, and colonization of multiple clones was supposed. CONCLUSION: vanA clusters in some E. gallinarum, and in E. faecalis or E. faecium isolates from the same patients had an identical structure, indicating their transfer from the latter. It is assumed that vanA type E. gallinarum can act as a reservoir of vanA gene for interspecies spread.

In Vitro Activities of Daptomycin Against Recent Clinical Isolates of Methicillin-resistant Staphylococci and Vancomycin-resistant Enterococci in Korea

BACKGROUND: Daptomycin is a novel cyclic lipopeptide antibiotic that exhibits in vitro bactericidal activity against gram-positive pathogens including methicillin-resistant staphylococci and vancomycin-resistant enterococci. The aim of this study is to determine the in vitro activities of daptomycin against recent clinical isolates of methicillin-resistant staphylococci and vancomycin-resistant enterococci in Korea. MATERIALS AND METHODS: A total of 117 clinical strains of methicillin-resistant staphylococci and vancomycin-resistant enterococci were isolated at a tertiary-care hospital in Korea in 2004. Susceptibility to daptomycin was tested by the CLSI broth microdilution method using Mueller-Hinton broth (MHB) which was adjusted to contain a final concentration of 50 microgram/mL of ionized calcium (Ca2+). Susceptibilities to ampicillin, oxacillin, levofloxacin, vancomycin, and linezolid were tested by the CLSI agar dilution method. RESULTS: All isolates of methicillin-resistant S. aureus and coagulase-negative staphylococci were inhibited by 1 microgram/mL of daptomycin, and MIC90s were 1 microgram/mL, which were similar to those of vancomycin and linezolid. MIC90s of daptomycin for vancomycin-resistant E. faecalis and E. faecium were 0.5 microgram/mL and 2 microgram/mL, respectively, and all isolates were susceptible to daptomycin. MIC90s of linezolid and levofloxacin for vancomycin-resistant enterococci were 1-2 microgram/mL and 64 microgram/mL, respectively. Resistance rates of vancomycin-resistant E. faecalis and E. faecium to levofloxacin were 100% and 96%, respectively. Daptomycin MICs in MHB supplemented to 20-25 microgram/ml of Ca2+ were 2-8 fold higher than those in MHB supplemented to 50 microgram/mL of Ca2+. CONCLUSION: Daptomycin is very active in vitro against methicillin-resistant staphylococci and vancomycin-resistant enterococci isolated in Korea, and it is important to test in vitro activity of daptomycin using MHB containing 50 microgram/mL of Ca2+.

In Vitro Activities of Daptomycin Against Recent Clinical Isolates of Methicillin-resistant Staphylococci and Vancomycin-resistant Enterococci in Korea

BACKGROUND: Daptomycin is a novel cyclic lipopeptide antibiotic that exhibits in vitro bactericidal activity against gram-positive pathogens including methicillin-resistant staphylococci and vancomycin-resistant enterococci. The aim of this study is to determine the in vitro activities of daptomycin against recent clinical isolates of methicillin-resistant staphylococci and vancomycin-resistant enterococci in Korea. MATERIALS AND METHODS: A total of 117 clinical strains of methicillin-resistant staphylococci and vancomycin-resistant enterococci were isolated at a tertiary-care hospital in Korea in 2004. Susceptibility to daptomycin was tested by the CLSI broth microdilution method using Mueller-Hinton broth (MHB) which was adjusted to contain a final concentration of 50 microgram/mL of ionized calcium (Ca2+). Susceptibilities to ampicillin, oxacillin, levofloxacin, vancomycin, and linezolid were tested by the CLSI agar dilution method. RESULTS: All isolates of methicillin-resistant S. aureus and coagulase-negative staphylococci were inhibited by 1 microgram/mL of daptomycin, and MIC90s were 1 microgram/mL, which were similar to those of vancomycin and linezolid. MIC90s of daptomycin for vancomycin-resistant E. faecalis and E. faecium were 0.5 microgram/mL and 2 microgram/mL, respectively, and all isolates were susceptible to daptomycin. MIC90s of linezolid and levofloxacin for vancomycin-resistant enterococci were 1-2 microgram/mL and 64 microgram/mL, respectively. Resistance rates of vancomycin-resistant E. faecalis and E. faecium to levofloxacin were 100% and 96%, respectively. Daptomycin MICs in MHB supplemented to 20-25 microgram/ml of Ca2+ were 2-8 fold higher than those in MHB supplemented to 50 microgram/mL of Ca2+. CONCLUSION: Daptomycin is very active in vitro against methicillin-resistant staphylococci and vancomycin-resistant enterococci isolated in Korea, and it is important to test in vitro activity of daptomycin using MHB containing 50 microgram/mL of Ca2+.

Prevalence of Inducible Clindamycin Resistance in Staphylococcal Isolates at a Korean Tertiary Care Hospital

Clindamycin resistance in Staphylococcus species can be either constitutive or inducible. Inducible resistance cannot be detected by the conventional antimicrobial susceptibility test. In this study, we determined the prevalence of inducible clindamycin resistance in staphylococcal isolates at a Korean tertiary care hospital. Between February and September 2004, 1,519 isolates of Staphylococcus aureus and 1,043 isolates of coagulase-negative staphylococci (CNS) were tested for inducible resistance by the D-zone test. Overall, 17% of MRSA, 84% of MSSA, 37% of MRCNS, and 70% of MSCNS were susceptible to clindamycin. Of the erythromycin non-susceptible, clindamycin-susceptible isolates, 32% of MRSA, 35% of MSSA, 90% of MRCNS, and 94% of MSCNS had inducible clindamycin resistance. Inducible clindamycin resistance in staphylococci was highly prevalent in Korea. This study indicates importance of the D-zone test in detecting inducible clindamycin resistance in staphylococci to aid in the optimal treatment of patients.

In Vitro Activities of Cefatrizine-Clavulanic Acid against Gram-Negative Bacilli Isolated from Community-acquired Urinary Track Infection / 대한진단검사의학회지

BACKGROUND: A high proportion of currently isolated gram-negative bacilli are resistant to beta-lactams by producing beta-lactamases. beta-lactam and beta-lactamase inhibitor combinations have been successfully used to overcome the resistance. In this study, in vitro antimicrobial activity of a new combination, cefatrizine-clavulanic acid, was determined against gram-negative bacilli isolated from community-acquired urinary track infections. METHODS: Nonduplicate strains of Enterobacteriaceae, isolated in 2003 from urine specimens of outpatients and inpatients of less than 3 hospital days at Severance Hospital, were tested by the NCCLS agar dilution method. RESULTS: Of a total of 204 isolates, 144 (71%) were Escherichia coli and 30 (15%) were Klebsiella spp. MIC50 and MIC90 of cefatrizine for E. coli were 2 microgram/mL and 16 microgram/mL, respectively. MIC90s of both cefaclor and cefoxitin were also 16 g/mL. MIC50 and MIC90 of cefatrizine-clavulanic acid for E. coli were 1 microgram/mL and 4 microgram/mL, respectively, which were 1/2-1/4 of those of cefaclor and cefoxitin. For Klebsiella spp., MIC90 of cefatrizine was 4 microgram/mL with an MIC range of 1->128 microgram/mL, whereas that of cefatrizine-clavulanic acid was 2 microgram/mL with an MIC range of 0.5-32 microgram/mL. In vitro activity of cefatrizine-clavulanic acid was higher than that of cefatrizine. CONCLUSIONS: Improved in vitro activity of cefatrizine-clavulanic acid against isolates of E. coli and Klebsiella spp. from community-acquired urinary track infection suggested that the combination is useful for an empirical treatment of the infection.

Emergence and Wide Dissemination of CTX-M-type ESBLs, and CMY-2- and DHA-1-type AmpC beta-Lactamases in Korean Respiratory Isolates of Klebsiella pneumoniae

Respiratory isolates of Klebsiella pneumoniae in Korea during 2002-2003 were studied to determine the prevalence and types of extended-spectrum beta-lactamases (ESBLs) and plasmid-mediated AmpC beta-lactamases (PABLs). ESBL-production was tested by double-disk synergy, and genotypes of beta-lactamases were determined by PCR and sequencing. ESBLs were detected in 28.4% of 373 isolates, and the most prevalent types were SHV-12 (63 isolates) and CTX-M-14 (9 isolates). Forty of 75 ESBL-producers (53.5%) also had PABLs: 21 isolates with CMY-2-like, 17 with DHA-1-like. Pulsed-field gel electrophoresis showed 19 types and 25 of 74 isolates had an identical pattern, indicating nosocomial spread. Dissemination of ESBL- and PABL-producing K. pneumoniae strains in Korea is a particular concern, as it limits the choice of antimicrobial agents for treatment of infections.

Antimicrobial Susceptibities and PFGE Patterns of Vancomycin-Resistant Enterococcus isolated from Clinical Specimens and Chickens / 대한진단검사의학회지

BACKGROUND: Enterococcal infections have become extremely difficult to manage because of an increase in antibiotic resistance among enterococci. In Europe, the use of avoparcin in animals was reported to be the cause of vancomycin-resistant enterococci (VRE) transmission to humans. In this study, we performed antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) to characterize the genetic relatedness of VRE of human and chicken. METHODS: Ninety strains of VRE were isolated from clinical specimens in three University hospitals located in Seoul and Kyungi province in 2001-2002. Thirty isolates of VRE were collected from four chicken farms located in areas remotely distanced from each other. The isolates were identified to the species level by conventional biochemical tests and commercial kits. Antimicrobial susceptibilities were tested by the NCCLS disk diffusion and agar dilution methods. For a molecular epidemiologic analysis, PFGE was performed. RESULTS: Among the 90 clinical isolates were 73 vancomycin-resistant Enterococcus faecium (VREFM) and 17 vancomycin-resistant E. faecalis (VREFA). The resistant rates of VREFA to ampicillin, levofloxacin and tetracycline were 0%, 100%, and 100%, respectively, and for VREFM, 100%, 96%, and 26%, respectively. However, the resistant rates of VREFM isolated from chicken were 19% to ampicillin, 0% to levofloxacin, and 100% to tetracycline. The PFGE patterns of genomic DNA of the clinical isolates were very diverse, suggesting a polyclonal spread of VRE, although some isolates had an identical PFGE pattern, indicating a mini-outbreak due to a clonal spread. The PFGE patterns of genomic DNA of the chicken isolates were very different from those of the human isolates. CONCLUSIONS: VRE isolates from human and chicken showed very different antimicrobial susceptibilities and PFGE patterns. These results suggest that VRE isolated from human and chicken are not closely related genetically.

In Vitro Activities of Panipenem against Clinical Isolates of Aerobic and Anaerobic Bacteria

BACKGROUND: Panipenem is a carbapenem antimicrobial agent which has been shown to have broad-spectrum activities against various aerobic and anaerobic bacteria. In this study, in vitro activities of panipenem against recent clinical isolates of aerobic and anaerobic bacteria were determined. METHODS: Aerobic and anaerobic bacteria were isolated in 2001 and in 2000-2001, respectively, from a tertiary-care hospital patients. Antimicrobial susceptibility was tested by the NCCLS agar dilution method. RESULTS: MIC90s of panipenem were:similar to those of imipenem for aerobic gram-positive cocci and Enterobacteriaceae; slightly lower than those of meropenem for gram-positive cocci, but slightly higher for Enterobacteriaceae; slightly higher than imipenem for A. baumannii, but similar for anaerobic bacteria. CONCLUSION: MIC90s of panipenem were similar to those of imipenem for aerobic and anaerobic bacterial isolates, which frequently involve respiratory, urinary, intraabdominal and wound infections. When imipenem breakpoints are applied to interpret panipenem susceptibilities, panipenem can be considered useful for the treatment of various infections, including nosocomially acquired ones.

In Vitro Activities of Panipenem against Clinical Isolates of Aerobic and Anaerobic Bacteria

BACKGROUND: Panipenem is a carbapenem antimicrobial agent which has been shown to have broad-spectrum activities against various aerobic and anaerobic bacteria. In this study, in vitro activities of panipenem against recent clinical isolates of aerobic and anaerobic bacteria were determined. METHODS: Aerobic and anaerobic bacteria were isolated in 2001 and in 2000-2001, respectively, from a tertiary-care hospital patients. Antimicrobial susceptibility was tested by the NCCLS agar dilution method. RESULTS: MIC90s of panipenem were:similar to those of imipenem for aerobic gram-positive cocci and Enterobacteriaceae; slightly lower than those of meropenem for gram-positive cocci, but slightly higher for Enterobacteriaceae; slightly higher than imipenem for A. baumannii, but similar for anaerobic bacteria. CONCLUSION: MIC90s of panipenem were similar to those of imipenem for aerobic and anaerobic bacterial isolates, which frequently involve respiratory, urinary, intraabdominal and wound infections. When imipenem breakpoints are applied to interpret panipenem susceptibilities, panipenem can be considered useful for the treatment of various infections, including nosocomially acquired ones.