BackgroundThe aim of this study was to investigate the molecular epidemiological characteristics of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa clinical isolates in Korea.Materials and MethodsThree hundred and twenty nine P. aeruginosa clinical isolates were collected from 23 general hospitals in Korea from March to June 2014. Species were identified by matrix-assited laser desorption/ionization-time of flight and 16S rRNA sequencing. Antimicrobial susceptibility was determined by disk diffusion methods. Further, minimum inhibitory concentrations of carbapenems were determined by Etest. Polymerase chain reaction and sequencing were performed to identify genes encoding MBLs. Multi-locus sequence typing and pulsed-field gel electrophoresis were performed to determine epidemiological characteristics of MBL-producing P. aeruginosa isolates.ResultsOf the 329 isolates, 229 (69.6%) were susceptible to the carbapenems tested, including imipenem and meropenem; while 100 (30.4%) were non-susceptible to more than one of the carbapenems. Genes encoding imipenemase-6 (IMP-6) and Verona imipenemase-2 (VIM-2) MBLs were identified in 21 (6.4%) isolates (n = 17 and 4, respectively). All MBL-producing isolates showed multi-drug resistant phenotype, and a majority (n = 19) of the isolates were identified as sequence type 235 (ST235). The remaining isolates (n = 2) were identified as ST309 and ST463.ConclusionP. aeruginosa ST235 might play an important role in dissemination of MBL genes in Korea.

Extended-spectrum cephalosporin (ESC)-resistant Enterobacteriaceae is an increasingly important problem in both human and veterinary medicine. The aims of this study were to describe a comparative molecular characterization of Enterobacteriaceae carrying ESC resistance genes, encoding extended-spectrum β-lactamase (ESBL) and AmpC, isolated from human stool samples, rectal swabs from companion animals, and swabs from the environment of veterinarian hospitals in South Korea, and to examine their possible dissemination and transmission. The ESC resistance genes were identified by PCR and sequencing. Isolates with the predominant ESC resistance genes were assessed for their genetic relatedness by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing. A total of 195 Escherichia coli and 41 Klebsiella pneumoniae isolates that exhibited ESC resistance were recovered on CHROMagar ESBL from human, companion animal, and the veterinary hospital environmental samples. In companion animals, most of the ESC resistance genes were bla CMY–2–like (26.4%), followed by bla CTX –M–55 (17.2%) and bla CTX–M–14 (16.1%), whereas bla CTX–M–15 (28.6%) was predominant in human samples. The epidemiological relatedness of isolates carrying ESC resistance genes, including 124 E. coli and 23 K. pneumoniae isolates carrying CMY-2-like, DHA-1-like, or/and CTX-M-type, were analyzed by PFGE. The pulsotypes of five E. coli isolates (three from dogs and two from humans) carrying bla CMY–2–like , which were attributed to sequence type 405, from different veterinary clinics showed >85% similarity. Our results indicate direct transmission and dissemination of ESC-resistant Enterobacteriaceae between humans and companion animals.

Tachyplesin I is a 17 amino acid, cationic, antimicrobial peptide with a typical cyclic antiparallel β-sheet structure. Interactions of tachyplesin I with living bacteria are not well understood, although models have been used to elucidate how tachyplesin I permeabilizes membranes. There are several questions to be answered, such as (i) how does tachyplesin I kill bacteria after it penetrates the membrane and (ii) does bacterial death result from the inactivation of intracellular esterases as well as cell injury? In this study, the dynamic antibacterial processes of tachyplesin I and its interactions with Escherichia coli and Staphylococcus aureus were investigated using laser confocal scanning microscopy in combination with electron microscopy. The effects of tachyplesin I on E. coli cell membrane integrity, intracellular enzyme activity, and cell injury and death were investigated by flow cytometric analysis of cells following single- or double-staining with carboxyfluorescein diacetate or propidium iodide. The results of microscopy indicated that tachyplesin I kills bacteria by acting on the cell membrane and intracellular contents, with the cell membrane representing the primary target. Microscopy results also revealed that tachyplesin I uses different modes of action against E. coli and S. aureus. The results of flow cytometry showed that tachyplesin I caused E. coli cell death mainly by compromising cell membrane integrity and causing the inactivation of intracellular esterases. Flow cytometry also revealed dynamic changes in the different subpopulations of cells with increase in tachyplesin I concentrations. Bacteria exposed to 5 μg/mL of tachyplesin I did not die instantaneously; instead, they died gradually via a sublethal injury. However, upon exposure to 10-40 μg/mL of tachyplesin I, the bacteria died almost immediately. These results contribute to our understanding of the antibacterial mechanism employed by tachyplesin I.

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bA total of 431 Pseudomonas aeruginosa clinical isolates were collected from 29 general hospitals in South Korea in 2015. Antimicrobial susceptibility was tested by the disk diffusion method, and MICs of carbapenems were determined by the agar dilution method. Carbapenemase genes were amplified by PCR and sequenced, and the structures of class 1 integrons surrounding the carbapenemase gene cassettes were analyzed by PCR mapping. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed for strain typing. Whole-genome sequencing was carried out to analyze P. aeruginosa genomic islands (PAGIs) carrying the bla IMP-6 , bla IMP-10 , and bla GES-24 genes. The rates of carbapenem-nonsusceptible and carbapenemase-producing P. aeruginosa isolates were 34.3% (148/431) and 9.5% (41/431), respectively. IMP-6 was the most prevalent carbapenemase type, followed by VIM-2, IMP-10, and GES-24. All carbapenemase genes were located on class 1 integrons of 6 different types on the chromosome. All isolates harboring carbapenemase genes exhibited genetic relatedness by PFGE (similarity > 80%); moreover, all isolates were identified as sequence type 235 (ST235), with the exception of two ST244 isolates by MLST. The bla IMP-6 , bla IMP-10 , and bla GES-24 genes were found to be located on two novel PAGIs, designated PAGI-15 and PAGI-16. Our data support the clonal spread of an IMP-6-producing P. aeruginosa ST235 strain, and the emergence of IMP-10 and GES-24 demonstrates the diversification of carbapenemases in P. aeruginosa in Korea. Pseudomonas aeruginosa is an opportunistic pathogen that causes various nosocomial infections, including sepsis, pneumonia, and urinary tract infections (1). Treatment of P. aeruginosa infections is often difficult because of the intrinsic drug resistance of P. aeruginosa and the ability of this pathogen to acquire genes for antimicrobial resistance determinants (2). Carbapenems are used as last-resort drugs for the treatment of infections caused by multidrug-resistant P. aeruginosa, due to their high affinity for penicillin-binding proteins, stability to various ␤-lactamases, and ability to easily pass through the bacterial outer membrane. However, the increasing use of carbapenems has resulted in the emerging phenomenon of carbapenem resistance (3).P. aeruginosa can become resistant to carbapenems by reduced permeability of the outer membrane due to loss of substrate-specific outer membrane porin OprD, frequently accompanied by AmpC hyperproduction and overexpression of efflux systems (4), along with acquisition of genes encoding carbapenemases (5). While the molecular mechanism of carbapenem resistance is geographically variable, diverse classes of carbapenemase have been increasingly identified in P. aeruginosa, including class A (KPC and GES variants), class B (IMP, VIM, and NDM metallo-␤-lactamases [MBLs]), and class D (OXA variants) (6). The MBLs, in particular IMP and VIM enzymes, are the most widespread carbapenemases in P. aeruginosa (7), with IMP-6 exclusivel...

BackgroundThe emergence of carbapenemase-producing Enterobacteriaceae (CPE) represents a major clinical problem because these bacteria are resistant to most antibiotics. CPE remain relatively uncommon in Korea. We report the prevalence, clinical characteristics, and molecular epidemiology of CPE isolates collected from five university hospitals in Korea.MethodsBetween January and December 2015, 393 non-duplicated isolates that were nonsusceptible to ertapenem were analyzed. Production of carbapenemase, extended-spectrum β-lactamase, and AmpC β-lactamase was determined by genotypic tests. Antimicrobial susceptibility profiles were determined by using an Etest. Clonality of Klebsiella pneumoniae carbapenemase (KPC)-2-producing and oxacillinase (OXA)-232-producing Klebsiella pneumoniae isolates was determined by pulsed-field gel electrophoresis (PFGE).ResultsOf the 393 isolates tested, 79 (20.1%) were CPE. Of these 79 isolates, 47 (59.5%) harbored the blaOXA-232 gene while the remaining isolates carried genes blaKPC-2 (n=27), blaIMP-1 (n=4), and blaNDM-1 (n=1). Among the 24 KPC-2 K. pneumoniae isolates from hospital B, 100% were resistant to carbapenems, 8% to colistin, and 0% to tigecycline. Among the 45 OXA-232 K. pneumoniae at hospital C, 95% were resistant to ertapenem, 68% to imipenem, 95% to meropenem, 10% to colistin, and 24% to tigecycline. PFGE analysis revealed a unique pattern for KPC-2 K. pneumoniae and identified 30 isolates belonging to the dominant pulsotypes (PT)1 and PT2 among 41 OXA-232 K. pneumoniae isolates.ConclusionsCPE strains are present in Korea, with the majority of K. pneumoniae isolates producing OXA-232 and KPC-2. The prevalence and predominant genotypes of CPE show hospital-specific differences.

This study attempted to evaluate whether oral lichen planus (OLP) has the potential to progress to oral squamous cell carcinoma (OSCC) by comparing the degree of genetic instability between clinically-curable OLP and lesions that progressed to OSCC. Fifteen cases of steroid-responsive OLP and two cases of lichenoid dysplasia (LD) that progressed to OSCC were used for this study. Chromosome in situ hybridization (CISH) was performed for chromosomes 9 and 17. The fraction of polysomic and monosomic cells for chromosome 9 increased in mucosal epithelium compared to those of lymphocytes in OLP. This difference was statistically significant (P=0.0017, 0.0054, respectively). Two LD patients showed 15.38% and 22.58% of PI for chromosome 9. In OSCC that developed from LD, the fraction of monosomic cells for chromosome 9 increased by more than 70%. We concluded that LD should be treated as a high-risk premalignant lesion and strongly suggest that the monosomy of chromosome 9 may have a critical role in progress to malignancy from LD.

In a future power system featuring significant renewable generation, the ability to manipulate domestic demand through the flexible operation of heat-led technologies such as heat pumps and micro-combined heat and power could be a critical factor in providing a secure and stable supply of electrical energy. Using a simulation-based approach, this study examined the linkage between the thermal characteristics of buildings and the scope for flexibility in the operating times of air source heat pumps. This was assessed against the resulting impact on the end-user’s comfort and convenience. A detached dwelling and flat were modelled in detail along with their heating system in order to determine the temporal shift achievable in the heat pump operating times for present-day and future dwellings. The simulation results indicated that the scope for shifting heat pump operating times in the existing building stock was limited, with time shifts of only 1–2 h achieved before there was a serious impact on the comfort of the occupant. However, if insulation levels were dramatically improved and substantial levels of thermal buffering were added into the heating system, sizable time shifts of up to 6 h were achievable without a significant impact on either space or hot water temperatures