We investigated an outbreak of Acinetobacter baumannii in an intensive care unit and in the surgery, medicine, neurology, and urology wards of the Kosin University Gospel Hospital in Busan, Korea. The outbreak involved 36 cases of infection by A. baumannii producing the OXA-23 ␤-lactamase over an 8-month period and was caused by a single pulsed-field gel electrophoresis clone. The epidemic isolates were characterized by a modified cloverleaf synergy test. Isoelectric focusing of crude bacterial extracts detected one nitrocefin-positive band with a pI value of 6.65. PCR amplification and characterization of the amplicons by direct sequencing indicated that the epidemic isolates carried a bla OXA-23 determinant. The epidemic isolates were characterized by a multidrug resistance phenotype that remained unchanged over the outbreak, including penicillins, cephamycins, extended-spectrum cephalosporins, carbapenems, monobactams, and aminoglycosides. This study shows that the bla OXA-23 resistance determinant may become an emerging therapeutic problem.Acinetobacter baumannii has emerged as an important nosocomial pathogen in outbreaks of hospital infections and is ranked second after Pseudomonas aeruginosa among nosocomial pathogens of aerobic nonfermentative gram-negative bacilli (17,19). A. baumannii causes respiratory and urinary tract infections, meningitis, endocarditis, burn infections, and wound sepsis, especially in intensive care units (ICUs) (4). A. baumannii infections are often difficult to eradicate due to high-level resistance to many antibiotics as a result of both intrinsic and acquired mechanisms. ␤-Lactamase production is the most important mechanism of acquired ␤-lactam resistance in gram-negative pathogens (21). Carbapenems (e.g., imipenem and meropenem) have become the drugs of choice against Acinetobacter infections in many centers but are being compromised by the emergence of carbapenem-hydrolyzing ␤-lactamase (carbapenemase) of molecular classes B and D (14). Class B carbapenemases found thus far in Acinetobacter spp. include various IMP-and VIM-type metallo-␤-lactamases (http: //www.lahey.org/studies/webt.asp), but most Acinetobacter spp. produce zinc-independent members of ␤-lactamase molecular class D (1). Sequenced carbapenemases of this latter class from that species include the following two distinct clusters: (i) the OXA-23-like cluster (OXA-23 and -27) and (ii) the OXA-24-like cluster . OXA-23 and OXA-27 have 99% amino acid identity, whereas they have only 60% identity with those of OXA-24-like cluster (1,3,6,7).Over an 8-month period from January to August 2003, 193 A. baumannii isolates were isolated from 193 patients hospitalized at the Kosin University Gospel Hospital. The purpose of the present study was to investigate an outbreak of A. baumannii in Korea and to characterize the imipenem resistance mechanism of the outbreak isolates. MATERIALS AND METHODS Bacterial strains and susceptibility tests. A total of 193 nonrepetitive clinical isolates of A. baumannii were isolated from Ja...

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 b-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 b-lactamase genes (bla CTX-M-3 fi 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.

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Aims: Isolates obtained from various regions in Korea in 2002 were identified and their susceptibility to extendedspectrum cephalosporins, monobactams and/or cephamycins was studied along with any production of extended-spectrum b-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 39AE2% 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 63AE3% 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 61AE5, 17AE3 and 7AE7% of strains respectively. About 51AE9% of strains contained more than two types of b-lactamase genes. Especially, one strain contained bla TEM , bla CMY and bla CTX-M genes. Significance: Resistance mechanisms to b-lactams, comprising mostly ESBL production, lead to the resistance against even recently developed b-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.