Il Kwon Bae

Investigation of a Nosocomial Outbreak of Imipenem-Resistant Acinetobacter baumannii Producing the OXA-23 β-Lactamase in Korea

ABSTRACT 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 β-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 blaOXA-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 blaOXA-23 resistance determinant may become an emerging therapeutic problem.

Molecular Characterization of Extended-Spectrum Beta-Lactamases Produced by Clinical Isolates of Klebsiella pneumoniae and Escherichia coli from a Korean Nationwide Survey

ABSTRACT To determine the prevalence and genotypes of extended-spectrum beta-lactamases (ESBLs) among clinical isolates of Klebsiella pneumoniae and Escherichia coli, we performed antibiotic susceptibility testing, pI determination, induction testing, transconjugation, and DNA sequencing analysis. Among the 509 isolates collected from 13 university hospitals in Korea, 39.2% produced ESBLs. ESBL-producing isolates were detected in every region in Korea. A total of 44.6% of the isolates produced both TEM- and SHV-type ESBLs, and 52% of ESBL-producing isolates transferred resistance to ceftazidime by transconjugation. The ESBLs were TEM-19, TEM-20, TEM-52, SHV-2a, SHV-12, and one new variant identified for the first time in Korea, namely, TEM-116. TEM-1 and SHV-12 were by far the most common variants. TEM-1, TEM-116, and SHV-12 showed a high prevalence in K. pneumoniae. Two isolates (E. coli SH16 and K. pneumoniae SV3) produced CMY-1-like beta-lactamases, which play a decisive role in resistance to cefoxitin and cefotetan, as well as TEM-type enzymes (TEM-20 and TEM-52, respectively). Using MIC patterns and DNA sequencing analysis, we postulated a possible evolution scheme among TEM-type beta-lactamases in Korea: from TEM-1 to TEM-19, from TEM-19 to TEM-20, and from TEM-20 to TEM-52.

Detection of Extended-Spectrum β-Lactamases by Using Boronic Acid as an AmpC β-Lactamase Inhibitor in Clinical Isolates of Klebsiella spp. and Escherichia coli

ABSTRACT We evaluated highly sensitive methods using boronic acid (BA) to detect extended-spectrum β-lactamase (ESBL) production. A total of 182 clinical isolates of Klebsiella spp. (n = 118) and Escherichia coli (n = 64) were analyzed: 62 harbored only ESBLs, 80 harbored both ESBLs and plasmid-mediated AmpC β-lactamases (pAmpCs), and 40 harbored only pAmpCs. The CLSI confirmatory test detected all isolates that produce only ESBLs but detected 85% of isolates that produce both enzymes. When a ≥5-mm increase in the zone diameter of either the cefotaxime (CTX) or the ceftazidime (CAZ) disk in the presence of both clavulanic acid (CA) and BA was considered to be a positive result, the test detected all isolates that harbor ESBLs (± pAmpCs) but showed frequent false-positive results (50%) for isolates that produce only pAmpCs. Meanwhile, when a ≥3-mm increase in the zone diameter of either the CTX/BA or the CAZ/BA disk in the presence of CA was considered to be a positive result, the test also detected all isolates that harbor ESBLs (± pAmpCs) and showed less frequent false-positive results (5%) in isolates that produce only pAmpCs. The latter new interpretive guideline has enhanced detection of ESBLs in clinical isolates of Klebsiella spp. and Escherichia coli and allowed detection of an ESBL even when potentially masked by a pAmpC.

Characterization of IncF plasmids carrying the blaCTX-M-14 gene in clinical isolates of Escherichia coli from Korea

OBJECTIVES The purpose of this study was to investigate the molecular epidemiology of CTX-M-14-producing Escherichia coli clinical isolates from Korea. METHODS A total of 138 non-duplicate E. coli clinical isolates showing reduced susceptibility or resistance to ceftazidime and/or cefotaxime were included in the study. Resistance genes, genetic environment, R plasmid size and replicon type, sequence type (ST) and XbaI-macrorestriction patterns were determined. RESULTS Among 138 isolates, 35 were found to carry the bla(CTX-M-14) gene. The ISEcp1 element was identified in the upstream region of the bla(CTX-M-14) gene in 32 isolates. The bla(CTX-M-14) gene was located on an IncF plasmid in 21 isolates, on an IncA/C plasmid in 1 isolate, on the chromosome in 8 isolates and on both the chromosome and an IncF plasmid in 5 isolates. The most prevalent ST was ST405 (n = 8), followed by ST354 (n = 4), ST38 (n = 3), ST69 (n = 3) and the intercontinental ST, ST131 (n = 3). PFGE and multilocus sequence typing experiments demonstrated no major clonal relationship among the CTX-M-14-producing isolates. CONCLUSIONS The bla(CTX-M-14) gene was probably mobilized by IncF plasmids, which can readily spread in E. coli, causing horizontal dissemination of the resistance gene in Korea.

First Outbreak of Klebsiella pneumoniae Clinical Isolates Producing GES-5 and SHV-12 Extended-Spectrum β-Lactamases in Korea

Klebsiella pneumoniae clinical isolates producing extended-spectrum β-lactamases (ESBLs; TEM and SHV types) are frequently implicated in hospital outbreaks. There are also reports of K. pneumoniae isolates producing various non-TEM, non-SHV ESBLs: CTX-M and GES/IBC types (1). Presently, the different GES-type ESBLs are designated by identical names (8). To clarify the misleading nomenclature of GES-type ESBLs, we propose maintaining the current denomination concerning the fully characterized GES-3 and GES-4 ESBLs reported by Wachino et al. (12, 13) and renaming the variants (GES-3 and GES-4) reported by Vourli et al. (11) as GES-5 and GES-6, respectively.

Epidemiology and Characteristics of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa

Metallo-β-lactamase-producing Pseudomonas aeruginosa (MPPA) is an important nosocomial pathogen that shows resistance to all β-lactam antibiotics except monobactams. There are various types of metallo-β-lactamases (MBLs) in carbapenem-resistant P. aeruginosa including Imipenemase (IMP), Verona integron-encoded metallo-β-lactamase (VIM), Sao Paulo metallo-β-lactamase (SPM), Germany imipenemase (GIM), New Delhi metallo-β-lactamase (NDM), Florence imipenemase (FIM). Each MBL gene is located on specific genetic elements including integrons, transposons, plasmids, or on the chromosome, in which they carry genes encoding determinants of resistance to carbapenems and other antibiotics, conferring multidrug resistance to P. aeruginosa. In addition, these genetic elements are transferable to other Gram-negative species, increasing the antimicrobial resistance rate and complicating the treatment of infected patients. Therefore, it is essential to understand the epidemiology, resistance mechanism, and molecular characteristics of MPPA for infection control and prevention of a possible global health crisis. Here, we highlight the characteristics of MPPA.

New definitions of extended-spectrum β-lactamase conferring worldwide emerging antibiotic resistance†

Although there is no consensus of the precise definition of ESBL, three kinds of ESBL definitions have been proposed. First, the classical definition includes variants derived from TEM‐1, TEM‐2, or SHV‐1; K1 (KOXY) of Klebsiella oxytoca. Second, the broadened definition has stretched the classical definition of ESBL to include: (1) β‐lactamases (CTX‐M‐ESBLs, GES‐ESBLs, and VEB‐ESBLs), with spectra similar to those of TEM and SHV variants (designated as TEM‐ and SHV‐ESBLs, respectively) but derived from other sources; (2) TEM and SHV variants with borderline ESBL activity; e.g., TEM‐12; and (3) various β‐lactamases conferring wider resistance than their parent types but not meeting the definition for group 2be; e.g., OXA‐types (OXA‐ESBLs) and mutant AmpC‐types (AmpC‐ESBLs), with increased activity against oxyimino‐cephalosporins and with resistance to clavulanic acid. Third, the all‐inclusive definition includes: (1) ESBLA (named for class A ESBLs); (2) ESBLM (miscellaneous ESBLs), which has been subdivided into ESBLM‐C (class C; plasmid‐mediated AmpC) and ESBLM‐D (class D); and (3) ESBLCARBA (ESBLs with hydrolytic activity against carbapenems), which has been subdivided into ESBLCARBA‐A (class A carbapenemases), ESBLCARBA‐B (class B carbapenemases), and ESBLCARBA‐D (class D carbapenemases). The consensus view about the ESBL definition is that the classical ESBL definition must be expanded to class A non‐TEM‐ and non‐SHV‐ESBLs (CTX‐M‐, GES‐, VEB‐ESBLs, etc.). However, these three definitions evoke rational debate on the question “Which would be included in the category of ESBLs among AmpC‐ESBLs, OXA‐ESBLs, and/or carbapenemases?” Therefore, there is a great need for consensus in the precise definition of ESBL.  © 2010 Wiley Periodicals, Inc. Med Res Rev 32:216‐232, 2012

Dissemination of transferable CTX-M-type extended-spectrum β-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 β‐lactamase (ESBL)‐producing isolates were investigated further to determine the mechanism of resistance.

Dissemination of IMP-6 metallo-β-lactamase-producing Pseudomonas aeruginosa sequence type 235 in Korea

OBJECTIVES To investigate the epidemiological traits of Pseudomonas aeruginosa clinical isolates producing metallo-β-lactamases (MBLs) in Korea. METHODS A total of 386 non-duplicate P. aeruginosa clinical isolates were collected from Korea in 2009. Detection of MBL genes was performed by PCR. The genetic organization of class 1 integrons carrying the MBL gene cassette was investigated by PCR mapping and sequencing. The epidemiological relationships of the isolates were investigated by multilocus sequence typing and PFGE. RESULTS Of 386 P. aeruginosa isolates, 30 (7.8%) isolates carried the bla(IMP-6) gene and 1 (0.3%) isolate carried the bla(VIM-2) gene. A probe specific for the bla(IMP-6) gene was hybridized to an ∼950 kbp I-CeuI-macrorestriction fragment from all 30 isolates and a probe specific for the bla(VIM-2) gene also hybridized to an ∼500 kbp I-CeuI-macrorestriction fragment from 1 isolate (BDC10). All 31 MBL-producing isolates shared an identical sequence type (ST), ST235, and they carried the same bla(OXA-50) allelic type, bla(OXA-50g). All MBL-producing isolates showed similar XbaI-macrorestriction patterns (similarity >85%), irrespective of MBL genotype. CONCLUSIONS P. aeruginosa ST235 carrying the chromosomally located bla(IMP-6) gene is widely disseminated in Korea.

Chromosome-encoded AmpC and CTX-M extended-spectrum β-lactamases in clinical isolates of Proteus mirabilis from Korea

ABSTRACT Among 222 Proteus mirabilis clinical isolates collected from 17 hospitals in Korea in 2008, 28 (12.6%) and 8 (3.6%) isolates exhibited extended-spectrum β-lactamase (ESBL) and AmpC phenotypes, respectively. The most common type of ESBL gene identified by PCR and sequencing experiments was bla CTX-M-14a (n = 12). The bla CTX-M-90 (n = 4), bla CTX-M-15 (n = 3), bla CTX-M-12 (n = 3), bla CTX-M-2 (n = 2), bla CTX-M-14b (n = 1), bla TEM-52 (n = 5), and bla SHV-12 (n = 1) genes were also detected. Eight isolates carried an AmpC β-lactamase gene, such as bla CMY-2 (n = 6) or bla DHA-1 (n = 2). All bla genes encoding CTX-M-1- and CTX-M-9-type enzymes and all bla CMY-2 genes were preceded by ISEcp1-like elements. The bla CTX-M-2 gene found in two isolates was located on a complex class 1 integron. The bla DHA-1 gene was preceded by a transcriptional regulator gene and was followed by phage shock protein genes. The bla CTX-M genes were located on the chromosome in 21 isolates. A plasmid location for the bla CTX-M gene was found in only four isolates: the bla CTX-M-14a gene was located on ∼150-kbp IncA/C plasmids in three isolates and on a ∼50-kbp IncN plasmid in one isolate. The bla TEM-52 gene was located on ∼50-kbp IncN plasmids in all five isolates. The AmpC β-lactamase genes were located on the chromosome in seven of eight isolates; one isolate carried the bla CMY-2 gene on a ∼150-kbp IncA/C plasmid. Our results show that a chromosomal location of CTX-M ESBL and AmpC β-lactamase genes in P. mirabilis is no longer an unusual phenomenon in hospital environments.