Dissemination of ceftazidime-resistant Acinetobacter baumannii clonal complex 92 in Korea.

AIMS: This study was performed to describe the epidemiological traits of ceftazidime-resistant Acinetobacter baumannii clinical isolates from Korea. METHODS AND RESULTS: Antimicrobial susceptibilities were determined by disk diffusion assay. PCR experiments were performed to detect genes encoding extended-spectrum ß-lactamases and metallo-ß-lactamases. Detection of ISAba1 upstream of the bla(ADC) gene was also performed by PCR amplification. The genetic organization of the bla(PER-1) gene was investigated by PCR mapping and sequencing of the regions surrounding the gene. Multilocus sequence typing was performed using seven housekeeping genes. A. baumannii isolates of clonal complex (CC) 92 exhibited a higher resistance rate (286/289, 99%) against ceftazidime compared to A. baumannii isolates of non-CC92 (7/87, 8%). Amongst 286 ceftazidime-resistant isolates of CC92, 100 (35%) isolates carried the bla(PER-1) gene, while none of the 87 isolates of non-CC92 carried the gene. The bla(ADC) gene associated with an ISAba1 element was detected in 98% (281/286) of ceftazidime-resistant isolates of CC92 and in all seven ceftazidime-resistant isolates of non-CC92. The bla(PER-1) gene was located on a transposon, Tn1213 (ISPa12-bla(PER-1) -Δgst-ISPa13), in 95 isolates and on a complex class 1 integron (orf513-bla(PER-1) -putative ABC transporter gene) in five isolates. Southern blot experiments confirmed the chromosomal location of the bla(PER-1) gene. CONCLUSIONS: Acinetobacter baumannii CC92 which has acquired ceftazidime resistance by the production of PER-1 extended-spectrum ß-lactamases and/or the overproduction of Acinetobacter-derived cephalosporinase is widely disseminated in Korea. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the mechanisms of acquiring ceftazidime resistance in A. baumannii and the epidemiological traits of ceftazidime-resistant A. baumannii isolates from Korea.

Investigation of a nosocomial outbreak of Acinetobacter baumannii producing PER-1 extended-spectrum beta-lactamase in an intensive care unit.

We investigated an outbreak of Acinetobacter baumannii in an adult intensive care unit of Kosin University Gospel Hospital in Busan, Republic of Korea. The outbreak involved 10 cases of infection by A. baumannii producing PER-1 extended-spectrum beta-lactamase over a seven-month period, and was caused by a single pulsed-field gel electrophoresis clone. The epidemic isolates were characterized by slight synergy between clavulanic acid and cefepime. Isoelectric focusing of crude bacterial extracts detected two nitrocefin-positive bands with pI values of 8.0 and 5.3. Polymerase chain reaction amplification and characterization of the amplicons by restriction analysis and direct sequencing indicated that the epidemic isolates carried a bla(PER-1) determinant. The epidemic isolates were characterized by a multidrug-resistant phenotype that remained unchanged over the outbreak, including penicillins, beta-lactam/beta-lactamase inhibitor, extended-spectrum cephalosporins and monobactams. Isolation of infected patients and appropriate carbapenem therapy were successful in ending the outbreak. Our report indicates that the bla(PER-1) resistance determinant may become an emerging therapeutic problem.

Association of the bla(CMY-10) gene with a novel complex class 1 integron carrying an ISCR1 element in clinical isolates from Korea.

The bla(CMY-10) gene responsible for ß-lactam resistance was located on a new complex class 1 integron within a conjugative plasmid. The sul1-type class 1 integron, containing an aadA2a gene cassette, was identified upstream of bla(CMY-10). A unique gene array (yqgF-yqgE-gshB-orf97--orf105) was identified downstream of bla(CMY-10.).

Dissemination of transferable CTX-M-type extended-spectrum beta-lactamase-producing Escherichia coli in Korea.

AIMS: Among 365 Escherichia coli isolated in 2003, 31 cefotaxime-resistant isolates were obtained from clinical specimens taken from adults hospitalized in Busan, Korea. Six extended-spectrum beta-lactamase (ESBL)-producing isolates were investigated further to determine the mechanism of resistance. METHODS AND RESULTS: These isolates were analysed by antibiotic susceptibility testing, pI determination, plasmid profiles, transconjugation test, PCR-restriction fragment length polymorphism (RFLP), enterobacterial repetitive consensus (ERIC)-PCR and DNA sequencing. All six of these isolates were found to contain the CTX-M-type ESBL genes. Five clinical isolates and their transconjugants produced CTX-M-3. One clinical isolate (K17391) and its transconjugant (trcK17391) produced CTX-M-15. Five clinical isolates also produced another TEM-1. One clinical isolate (K12776) also contained another TEM-52. CTX-M-3 ESBL gene was responsible for the resistance to piperacillin, cephalothin, cefotaxime, cefepime and aztreonam. CTX-M-15 or TEM-52 was especially responsible for the resistance to ceftazidime. CONCLUSIONS: These results appear to represent the in vivo evolution of CTX-M-type beta-lactamase genes (bla(CTX-M-3) --> bla(CTX-M-15)) under the selective pressure of antimicrobial therapy (especially ceftazidime). PCR-RFLP is a reliable method to discriminate CTX-M-15 gene from CTX-M-3 gene. ERIC-PCR analysis revealed that dissemination of CTX-M-3 was not due to a clonal outbreak of a resistant strain but to the intra-species spread of resistance to piperacillin, cephalothin, cefotaxime, cefepime and aztreonam in Korea. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of the occurrence of CTX-M-1 cluster ESBLs in Korea. A more comprehensive survey of these ESBL types from Korea is urgently needed because of the in vivo evolution of CTX-M-15 from CTX-M-3. The emergence of these CTX-M-type ESBLs suggests that diagnostic laboratories should screen for ESBLs with ceftazidime as well as cefotaxime; they should still perform clavulanate synergy tests on resistant isolates.

Investigation of extended-spectrum beta-lactamases produced by clinical isolates of Klebsiella pneumoniae and Escherichia coli in Korea.

AIMS: Isolates obtained from various regions in Korea in 2002 were identified and their susceptibility to extended-spectrum cephalosporins, monobactams and/or cephamycins was studied along with any production of extended-spectrum beta-lactamases (ESBLs). METHODS AND RESULTS: Bacteria identified by the conventional techniques and Vitek GNI card were Klebsiella pneumoniae and Escherichia coli. Using disk diffusion and double-disk synergy tests, we found that 39.2% of strains produced ESBLs. About 52% of isolates transferred resistance to ceftazidime by conjugation. Banding patterns of PCR amplification with the designed primers showed that 837- and 259-bp fragments specific to bla(TEM) genes were amplified in 63.3% of strains. 929- and 231-bp fragments (bla(SHV)), 847- and 520-bp fragments (bla(CMY)), 597- and 858-bp fragments (bla(CTX-M)) were amplified in 61.5, 17.3 and 7.7% of strains respectively. About 51.9% of strains contained more than two types of beta-lactamase genes. Especially, one strain contained bla(TEM), bla(CMY) and bla(CTX-M) genes. SIGNIFICANCE: Resistance mechanisms to beta-lactams, comprising mostly ESBL production, lead to the resistance against even recently developed beta-lactams in enterobacteria, which is now a serious threat to antibiotic therapy. The high prevalence of bla(CMY) genes and multidrug-resistant genes may also make therapeutic failure and lack of eradiation of these strains by extended-spectrum cephalosporins or cephamycins.