Prevalence of Ambler Class A Extended-Spectrum beta-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Isolates in Korea / 대한임상미생물학회지

BACKGROUND: The aim of this study is to determine the nationwide prevalence of Ambler class A extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae and to characterize genotypes of ESBLs. METHODS: During the period of February through July, 2003, E.coli and K.pneumoniae isolates were collected from 12 hospitals in Korea. Antimicrobial susceptibilities were tested by disk diffusion method, and ESBL-production was determined by the double-disk synergy test. MICs of beta-lactam antibiotics were tested by agar dilution method. Searches for bla TEM, bla SHV, bla CTX-M, bla PER-1, bla VEB, bla IBC, bla GES and bla TLA genes were performed by PCR amplification, and the genotypes of ESBLs were determined by direct nucleotide sequence analysis of amplified products. RESULTS: Resistance rates of E.coli (n=246) and K.pneumoniae (n=239) isolates to ceftazidime were 8.5% and 20.1%, respectively. Most prevalent Ambler class A ESBL genotypes in E.coli isolates were bla CTX-M-15 (n=4) and bla CTX-M-3 (n=3), and each of bla CTX-M-14, bla SHV-12, and bla TEM-52 gene was also found in one isolate. Most prevalent ESBL genotypes in K.pneumoniae were bla SHV-12 (n=30) and bla CTX-M-3 (n=13), and bla CTX-M-14 (n=5). bla SHV-2a (n=3), bla SHV-5 (n=2), bla TEM-52 (n=1), bla GES-3 (n=2) genes were also found. CONCLUSION: CTX-M-type ESBL-producing E.coli and K.pneumoniae isolates are spreading, and a GES-type ESBL has emerged in Korea.

Prevalence of Imipenem-Resistant Pseudomonas aeruginosa Isolates and Mechanisms of Resistance / 대한임상미생물학회지

BACKGROUND: Spread of imipenem-resistant Pseudomonas aeruginosa isolates is an important clinical threat. The aim of this study is to survey the prevalence of carbapenem-resistant P.aeruginosa isolates in a university hospital, Busan, Korea, and to determine the mechanisms of the resistance. METHODS: P.aeruginosa isolates from the patients in Kosin University Gospel Hospital were collected during the period of June through September, 2004. Antimicrobial susceptibilities were tested by the disk diffusion method, and production of carbapenemase and metallo-beta-lactamase was determined by the modified Hodge and EDTA-disk synergy tests, respectively. MICs were determined by the agar dilution method, and pIs of beta-lactamases were determined by the isoelectric focusing. Genotypes of carbapenemases were determined by direct sequencing of amplified products. RESULTS: A total of 77 clinical isolates of P.aeruginosa were collected. Twenty-two (55.0%) and 15 (37.5%) isolates showed positive results in the modified Hodge and EDTA-disk synergy tests, re-spectively. Searches for bla OXA-23 and bla IMP-1 genes showed positive results in 15 and 12 isolates, respectively. MIC ranges of imipenem and meropenem to OXA-23-producing isolates were 8-16 microgram/mL and 2-32 microgram/mL, respectively, and those to IMP-1-producing isolates were 2-> or =256 microgram/mL and 2-128 microgram/mL, respectively. CONCLUSION: Production of OXA-23 or IMP-1 is the most prevalent mechanism of imipenem-resistance in P.aeruginosa isolates in a university hospital, Busan, Korea. Periodical surveys are necessary to monitor the spreading of imipenem-resistant isolates and emerging new mechanisms of imipenem-resistance.

Emergence of CTX-M-9 Extended-Spectrum beta-Lactamase-Producing Enterobacter cloacae Isolates / 대한임상미생물학회지

BACKGROUND: The aim of this study is to assess the prevalence and to investigate the molecular epidemiology of Ambler class A extended-spectrum beta-lactamase (ESBL)-producing Enterobacter cloacae isolates in a university hospital in Busan, Korea. METHODS: Non-duplicated clinical isolates of E.cloacae from patients admitted in Kosin University Gospel Hospital were collected during the period from January through September, 2003. ESBL-production was examined by the double-disk synergy test (DDST) and the transferability of cefotaxime-resistance by conjugation. MICs of beta-lactam antibiotics were determined by the agar dilution method and Ambler class A ESBL genes were searched by PCR amplification. Enterobacterial repetitive intergenic consensus (ERIC) PCR was performed to investigate epidemiological relationships among bla CTX-M-9 gene-carrying E.cloacae isolates. RESULTS: Antimicrobial resistance rates of E.cloacae isolates (n=148) to ceftazidime, cefotaxime, and aztreonam were 50.0%, 29.6%, and 48.0%, respectively. Among 50 E.cloacae isolates intermediate or resistant to more than one expanded-spectrum beta-lactam agent, 41 (27.7%) showed positive results in DDST; of these 41 isolates, 1 was found to carry bla TEM-52 gene, 16 carried bla SHV-12 gene, 4 bla CTX-M-9 gene, and 19 both bla SHV-12 and bla CTX-M-9 genes. The 23 E.cloacae isolates carrying bla CTX-M-9 gene showed 9 different profiles by ERIC PCR. CONCLUSION: ESBL-producing E.cloacae was not uncommon in a university hospital in Busan, Korea. The commonest types of ESBLs produced by E.cloacae isolates were SHV-12 and CTX-M-9. CTX-M-9 ESBL-producing E.cloacae isolates showed diverse ERIC-PCR profiles, indicating that they were not originated from a common source.

Prevalence of CTX-M-type Extended-Spectrum beta-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Isolates in Korea, 2003 / 대한임상미생물학회지

BACKGROUND: The aims of this study were to survey nationwide susceptibilities of Escherichia coli and Klebsiella pneumoniae isolates against cefotaxime and to determine the prevalences of CTX-Mtype extended-spectrum beta-lactamases(ESBLs). METHODS: During the period of February to July, 2003, E. coli and K. pneumoniae isolates were collected from 12 hospitals. Antimicrobial susceptibilities to cefotaxime were tested by the disk diffusion method. ESBL production was determined by the double disk synergy test. Cefotaxime-resistance of the ESBL-producers was transfered to E. coli DH5alphaand E. coli Top10-F by transformation. MICs of beta-lactam antibiotics were determined by the agar dilution method. Searches for blaCTX-M genes was performed by PCR amplication; pIs of beta-lactamases were determined by isoelectric focusing. RESULTS: Among 230 isolates of E. coli and 232 isolates of K. pneumoniae, 27 (11.7%) and 79 (34.1%) were intermediate or resistant to cefotaxime, respectively. Twenty-four (10.4%) isolates of E. coli and 58 (25.0%) K. pneumoniae isolates showed positive results in the double disk synergy test. Three isolates of E. coli and 13 K. pneumoniae isolates harbored blaCTX-M-3 gene, 4 E. coli isolates harbored blaCTX-M-15 gene, and 1 E. coli and 5 K. pneumoniae isolates harbored blaCTX-M-14 gene. CONCLUSION: E. coli and K. pneumoniae isolates producing CTX-M-type ESBLs were not uncommon in Korean hospitals. It is thought that periodical surveys are necessary for inspecting the spread of CTX-M-type ESBL genes are necessary.

Prevalence of OXA-23 Extended-Spectrum beta-Lactamase-Producing Clinical Isolates of Acinetobacter baumannii in a University Hospital, Busan, Korea / 대한임상미생물학회지

BACKGROUND: Acinetobacter baumannii is a glucose-nonfermenting gram-negative rod and is a well-recognized nosocomial pathogen. In recent years, A. baumannii strains showing resistance to carbapenems by producing metallo-beta-lactamases or OXA-type beta-lactamases have increased, and it is considered to be a serious clinical problem. But genotypes of carbapenemases produced by A. baumannii isolates in Korea have been rarely reported. The purpose of this study was to investigate the prevalence of imipenem-resistant A. baumannii and to determine the mechanism of resistance. METHODS: During the period of January through September, 2003, susceptibilities to imipenem of A. baumannii isolates from patients admitted in Kosin University Gospel Hospital in Busan, Korea were investigated. The modified Hodge and EDTA-disk synergy tests were performed for screening of carbapenemase and metallo-beta-lactamase-production. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. For detection of IMP, VIM and OXA-type beta-lactamases genes, polymerase chain reactions (PCR) were performed, and the DNA sequences of OXA-type beta-lactamases genes were determined by using the dideoxy-chain termination method. The isoelectric points of beta-lactamases were determined by isoelectric focusing. Pulsed-field gel electrophresis (PFGE) of the SmaI-digested genomic DNA was performed. RESULTS: A total of 193 strains of A. baumannii were collected from patients during the surveillance period. Twenty-seven percents (52/193) of A. baumannii isolates were resistant to imipenem. Among the 52 imipenem-resistant isolates, 41 isolates (78.8%) showed positive results in the modified Hodge test, but none of the isolates showed positive results in the EDTA-disk synergy test. Thirty-eight modified Hodge test-positive isolates harbored blaOXA-23 gene, but none of the isolates harbored IMP- or VIM-type metallo-beta-lactamases genes. Analytical isoelectric focusing revealed that all the 38 isolates had a nitrocefin-positive band at pI of 6.65. Thirty-five OXA-23-producing isolatesshowed a similar PFGE pattern when digested by SmaI endonuclease. CONCLUSION: Thirty-eight clinical isolates of A. baumannii acquired resistance to imipenem by producing OXA-23 beta-lactamase. Among them were 35 isolates thought to be originated from the same source, because they contained a similar chromosomal type. To the best of our knowledge, this is the first time that OXA-23 beta-lactamase has been detected in Korea.

Prevalence of PER-1 Extended-Spectrum beta-Lactamase-Producing Clinical Isolates of Acinetobacter baumannii in a University Hospital, Busan, Korea / 대한임상미생물학회지

BACKGROUND: In recent years, Acinetobacter baumannii isolates acquired resistance to cefepime have increased significantly. The aim of this study was to survey the prevalence of PER-1 extendedspectrum beta -lactamase (ESBL)-producing A. baumannii isolates in a University Hospital, Busan, Korea. METHODS: Antimicrobial susceptibilities were tested by the disk diffusion method, and double disk synergy test was performed for screening of ESBL-production. MICs were determined by agar dilution method. The isoelectric points of beta -lactamases were determined by isoelectric focusing. Transferability of cefepime-resistance were tested by conjugation. blaPER-1 and blaPER-2 alleles were detected by PCR, and the DNA sequences of amplified products were determined by using the dideoxy-chain termination method. RESULTS: Among 51 clinical isolates of A. baumannii intermediate or resistant to cefepime, 10 isolates (19.6%) showed positive results in double disk synergy test. PCR-based experiments detected blaPER-1 gene in all the 10 isolates. All the isolates contained three beta -lactamase bands: pI 5.3, 7.9, and 9.4. MICs of ampicillin, piperacillin, cephalothin, cefoxitin, cefoperazone, ceftazidime, cefotaxime, cefepime, and aztreonam were >256 mg/L, respectively, and them of imipenem were 8-16 mg/L. CONCLUSION: The prevalence of PER-1-producing A. baumannii strains in Busan was less than that of in Seoul. But an outbreak of infection caused by this strain in an intensive care unit shows that spread of PER-1-producing A. baumannii strains can be anticipated in a near future. Prevention of hospital infection by these resistant microorganisms are needed.

Prevalence of CTX-M-type Extended-Spectrum beta-Lactamase-Producing Esherichia coli and Klebsiella pneumoniae Isolates in Korea / 대한임상미생물학회지

BACKGROUND: The aim of this study was to survey the nation wide susceptibilities of Esherichia coli and Klebsiella pneumoniae against cefotaxime and to determine the prevalence of CTX-M-type extended-spectrum beta- lactamases(ESBLs). METHODS: During the period of April to June, 2002, E. coli and K. pneumoniae isolates were collected from 13 hospitals. Antimicrobial susceptibilities to cefotaxime were tested by the disk diffusion method. ESBL production was determined by double disk synergy test. Cefotaxime-resistance of the ESBL-producers was transferred to azide-resistant E. coli J53 by conjugation. MICs of beta- lactam antibiotics were determined by agar dilution method. Searches for blaCTX-M genes were performed by PCR amplication. pIs of beta-lactamases were determined by isoelectric focusing. RESULTS: Ten percents of E. coli and 35 percents of K. pneumoniae isolates among 260 strains of each were intermediate or resistant to cefotaxime. Twenty-three isolates of E. coli and 78 K. pneumoniae isolates showed positive results in the double disk synergy test. One isolate of E. coli and 2 K. pneumoniae isolates harbored blaCTX-M-3 gene, 2 E. coli isolates harbored blaCTX-M-15 gene, and 2 E. coli and 2 K. pneumoniae isolates harbored blaCTX-M-14 gene. CONCLUSION: E. coli and K. pneumoniae isolates producing CTX-M-type ESBLs are not uncommon in Korean hospitals. The spread of CTX-M-type ESBL genes could compromise the future usefulness of 3rd generation cephalosporins and aztreonam for the treatment of E. coli and K. pneumoniae infections.