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Search Results: 1 - 10 of 209181 matches for " L. Kristopher Siu "
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A Case of Carbapenem Resistant Non-K1/K2 Serotype Klebsiella pneumoniae Liver Abscess  [PDF]
Lucy Cheng, Leung Kristopher Siu, Tom Chiang
Advances in Infectious Diseases (AID) , 2013, DOI: 10.4236/aid.2013.33032
Abstract:

Klebsiella pneumoniae liver abscess (KPLA) has been described as an invasive syndrome with extrahepatic complications. The majority of KPLA is caused by capsular serotype K1 and K2 isolates. We report a case of carbapenem resistant Klebsiella pneumoniae liver abscess. The patient initially presented with infected right above-the-knee amputation and was later found with a large liver abscess. Initial antimicrobial susceptibility showed carbapenem resistant K. pneumoniae (CRKP). Further molecular workup revealed that the isolate was a less virulent non-K1/K2 serotype, and both rmpA and kfu genes were negative. The lack of outer membrane porins likely contributed to the carbapenem resistance. To our knowledge, this is a first reported case of carbapenem resistant, non-K1/K2 serotype K. pneumoniae liver abscess in the United States.

Sequence of Closely Related Plasmids Encoding blaNDM-1 in Two Unrelated Klebsiella pneumoniae Isolates in Singapore
Ying-Tsong Chen, Ann-Chi Lin, L. Kristopher Siu, Tse Hsien Koh
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0048737
Abstract: Background Spread of the blaNDM-1 gene that encodes the New Delhi metallo-β-lactamase (NDM-1) in Enterobacteriaceae is a major global health problem. Plasmids carrying blaNDM-1 from two different multi-drug resistant Klebsiella pneumonia isolates collected in Singapore were completely sequenced and compared to known plasmids carrying blaNDM-1. Methodology/Principal Findings The two plasmids, pTR3 and pTR4, were transferred to Escherichia coli recipient strain J53 and completely sequenced by a shotgun approach using 3-kb paired-end libraries on 454. Although the K. pneumoniae strains were unrelated by molecular typing using PFGE and MLST, complete sequencing revealed that pTR3 and pTR4 are identical. The plasmid sequence is similar to the E. coli NDM-1-encoding plasmid p271A, which was isolated in Australia from a patient returning from Bangladesh. The immediate regions of the blaNDM-1 gene in pTR3/4 are identical to that of p271A, but the backbone of our plasmid is much more similar to another IncN2 plasmid reported recently, pJIE137, which contained an additional 5.2-kb CUP (conserved upstream repeat) regulon region in comparison to p271A. A 257-bp element bounded by imperfect 39-bp inverted repeats (IR) and an incomplete version of this element flanking the 3.6-kb NDM-1-encoding region were identified in these plasmids and are likely to be the vestiges of an unknown IS. Conclusions Although the hosts are not epidemiologically linked, we found that the plasmids bearing the blaNDM-1 gene are identical. Comparative analyses of the conserved NDM-1-encoding region among different plasmids from K. pneumoniae and E. coli suggested that the transposable elements and the two unknown IR-associated elements flanking the NDM-1-encoding region might have aided the spreading of this worrisome resistance determinant.
Single or in Combination Antimicrobial Resistance Mechanisms of Klebsiella pneumoniae Contribute to Varied Susceptibility to Different Carbapenems
Yu-Kuo Tsai, Ci-Hong Liou, Chang-Phone Fung, Jung-Chung Lin, L. Kristopher Siu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079640
Abstract: Resistance to carbapenems has been documented by the production of carbapenemase or the loss of porins combined with extended-spectrum β-lactamases or AmpC β-lactamases. However, no complete comparisons have been made regarding the contributions of each resistance mechanism towards carbapenem resistance. In this study, we genetically engineered mutants of Klebsiella pneumoniae with individual and combined resistance mechanisms, and then compared each resistance mechanism in response to ertapenem, imipenem, meropenem, doripenem and other antibiotics. Among the four studied carbapenems, ertapenem was the least active against the loss of porins, cephalosporinases and carbapenemases. In addition to the production of KPC-2 or NDM-1 alone, resistance to all four carbapenems could also be conferred by the loss of two major porins, OmpK35 and OmpK36, combined with CTX-M-15 or DHA-1 with its regulator AmpR. Because the loss of OmpK35/36 alone or the loss of a single porin combined with blaCTX-M-15 or blaDHA-1-ampR expression was only sufficient for ertapenem resistance, our results suggest that carbapenems other than ertapenem should still be effective against these strains and laboratory testing for non-susceptibility to other carbapenems should improve the accurate identification of these isolates.
Do Neutrophils Play a Role in Establishing Liver Abscesses and Distant Metastases Caused by Klebsiella pneumoniae?
Jung-Chung Lin,Feng-Yee Chang,Chang-Phone Fung,Kuo-Ming Yeh,Chiung-Tong Chen,Yu-Kuo Tsai,L. Kristopher Siu
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0015005
Abstract: Serotype K1 Klebsiella pneumoniae is a major cause of liver abscesses and endophthalmitis. This study was designed to identify the role of neutrophils in the development of distant metastatic complications that were caused by serotype K1 K. pneumoniae. An in vitro cellular model was used to assess serum resistance and neutrophil-mediated killing. BALB/c mice were injected with neutrophils containing phagocytosed K. pneumoniae. Serotype K1 K. pneumoniae was significantly more resistant to serum killing, neutrophil-mediated phagocytosis and intra-cellular killing than non-K1 isolates (p<0.01). Electron microscopic examination had similar findings as in the bioassay findings. Intraperitoneal injection of neutrophils containing phagocytosed serotype K1 K. pneumoniae led to abscess formation in multiple sites including the subcutaneous tissue, lung, and liver, whereas no abscess formation was observed in mice injected with non-K1 isolates. The resistance of serotype K1 K. pneumoniae to complement- and neutrophil-mediated intracellular killing results in the dissemination of K. pneumoniae via the bloodstream. Escape from neutrophil intracellular killing may contribute to the dissemination and establishment of distant metastases. Thus, neutrophils play a role as a vehicle for helping K. pneumoniae and contributing to the establishment of liver abscess and distant metastatic complications.
Seroepidemiology of Klebsiella pneumoniae colonizing the intestinal tract of healthy chinese and overseas chinese adults in Asian countries
Yi-Tsung Lin, L Kristopher Siu, Jung-Chung Lin, Te-Li Chen, Chih-Peng Tseng, Kuo-Ming Yeh, Feng-Yee Chang, Chang-Phone Fung
BMC Microbiology , 2012, DOI: 10.1186/1471-2180-12-13
Abstract: Serotypes K1/K2 accounted for 9.8% of all K. pneumoniae isolates from stools in all countries. There was no significant difference in the prevalence of K1/K2 isolates among the countries excluding Thailand and Vietnam. The antimicrobial susceptibility pattern was nearly the same in K. pneumoniae isolates. The result of pulsed-field gel electrophoresis revealed no major clonal cluster of serotype K1 isolates.The result showed that Chinese ethnicity itself might be a major factor predisposing to intestinal colonization by serotype K1/K2 K. pneumoniae isolates. The prevalent serotype K1/K2 isolates may partially correspond to the prevalence of K. pneumoniae liver abscess in Asian countries.Klebsiella pneumoniae is responsible for a wide spectrum of clinical syndromes, including purulent infections, urinary tract infections, pneumonia, bacteremia, septicemia, and meningitis [1]. In the past three decades, K. pneumoniae has emerged as the single leading cause of pyogenic liver abscess in East Asian countries, especially in Taiwan [2-7]. An invasive syndrome of liver abscess complicated by meningitis, endophthalmitis or other metastatic suppurative foci has been reported, and capsular serotypes K1 and K2 of K. pneumoniae are thought to the major virulence determinants responsible for this syndrome [3,6,8]. In an analysis of K. pneumoniae liver abscess from two hospitals in New York by Rahimian et al. [9], 78.3% of patients were of Asian origin. These findings raise the possibility that genetic susceptibility to or geographic distribution patterns of virulent K. pneumoniae subtypes may play important roles [10].The intestine is one of the major reservoirs of K. pneumoniae, and epidemiological studies have suggested that the majority of K. pneumoniae infections are preceded by colonization of the gastrointestinal tract [11]. The possibility of fecal-oral transmission has been raised on the basis of molecular typing of isolates from siblings, family members, and the environm
National Surveillance Study on Carbapenem Non-Susceptible Klebsiella pneumoniae in Taiwan: The Emergence and Rapid Dissemination of KPC-2 Carbapenemase
Sheng-Kang Chiu, Tsu-Lan Wu, Yin-Ching Chuang, Jung-Chung Lin, Chang-Phone Fung, Po-Liang Lu, Jann-Tay Wang, Lih-Shinn Wang, L. Kristopher Siu, Kuo-Ming Yeh
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069428
Abstract: Objectives The global spread and increasing incidence of carbapenem non-susceptible Klebsiella pneumoniae (CnSKP) has made its treatment difficult, increasing the mortality. To establish nationwide data on CnSKP spread and carbapenem-resistance mechanisms, we conducted a national surveillance study in Taiwanese hospitals. Methods We collected 100 and 247 CnSKP isolates in 2010 and 2012, respectively. The tests performed included antibiotic susceptibility tests; detection of carbapenemase, extended-spectrum β-lactamases (ESBL), and AmpC β-lactamases genes; outer membrane porin profiles; and genetic relationship with pulsed-field gel electrophoresis and multilocus sequence type. Results The resistance rate of CnSKP isolates to cefazolin, cefotaxime, cefoxitin, ceftazidime, and ciprofloxacin was over 90%. Susceptibility rate to tigecycline and colistin in 2010 was 91.0% and 83.0%, respectively; in 2012, it was 91.9% and 87.9%, respectively. In 2010, carbapenemase genes were detected in only 6.0% of isolates (4 blaIMP-8 and 2 blaVIM-1). In 2012, carbapenemase genes were detected in 22.3% of isolates (41 blaKPC-2, 7 blaVIM-1, 6 blaIMP-8, and 1 blaNDM-1). More than 95% of isolates exhibited either OmpK35 or OmpK36 porin loss or both. Impermeability due to porin mutation coupled with AmpC β-lactamases or ESBLs were major carbapenem-resistance mechanisms. Among 41 KPC-2-producing K. pneumoniae isolates, all were ST11 with 1 major pulsotype. Conclusions In 2010 and 2012, the major mechanisms of CnSKP in Taiwan were the concomitance of AmpC with OmpK35/36 loss. KPC-2-KP dissemination with the same ST11 were observed in 2012. The emergence and rapid spread of KPC-2-KP is becoming an endemic problem in Taiwan. The identification of NDM-1 K. pneumoniae case is alarming.
Review of Inverse Laplace Transform Algorithms for Laplace-Space Numerical Approaches
Kristopher L. Kuhlman
Mathematics , 2012, DOI: 10.1007/s11075-012-9625-3
Abstract: A boundary element method (BEM) simulation is used to compare the efficiency of numerical inverse Laplace transform strategies, considering general requirements of Laplace-space numerical approaches. The two-dimensional BEM solution is used to solve the Laplace-transformed diffusion equation, producing a time-domain solution after a numerical Laplace transform inversion. Motivated by the needs of numerical methods posed in Laplace-transformed space, we compare five inverse Laplace transform algorithms and discuss implementation techniques to minimize the number of Laplace-space function evaluations. We investigate the ability to calculate a sequence of time domain values using the fewest Laplace-space model evaluations. We find Fourier-series based inversion algorithms work for common time behaviors, are the most robust with respect to free parameters, and allow for straightforward image function evaluation re-use across at least a log cycle of time.
Unsaturated Hydraulic Conductivity Models Based on Truncated Lognormal Pore-size Distributions
Bwalya Malama,Kristopher L. Kuhlman
Physics , 2013, DOI: 10.1111/gwat.12220
Abstract: We develop a closed-form three-parameter model for unsaturated hydraulic conductivity associated with the Kosugi three-parameter lognormal moisture retention model. The model derivation uses a slight modification to Mualem's theory, which is nearly exact for non-clay soils. Kosugi's three-parameter lognormal moisture retention model uses physically meaningful parameters, but a corresponding closed-form relative hydraulic conductivity model has never been developed. The model is further extended to a four -parameter model by truncating the underlying pore size distribution at physically permissible minimum and maximum pore radii. The proposed closed-form models are fitted to well-known experimental data, to illustrate their utility. They have the same physical basis as Kosugi's two-parameter model, but are more general.
Unconfined Aquifer Flow Theory - from Dupuit to present
Phoolendra K. Mishra,Kristopher L. Kuhlman
Physics , 2013, DOI: 10.1007/978-1-4614-6479-2_9
Abstract: Analytic and semi-analytic solution are often used by researchers and practicioners to estimate aquifer parameters from unconfined aquifer pumping tests. The non-linearities associated with unconfined (i.e., water table) aquifer tests makes their analysis more complex than confined tests. Although analytical solutions for unconfined flow began in the mid-1800s with Dupuit, Thiem was possibly the first to use them to estimate aquifer parameters from pumping tests in the early 1900s. In the 1950s, Boulton developed the first transient well test solution specialized to unconfined flow. By the 1970s Neuman had developed solutions considering both primary transient storage mechanisms (confined storage and delayed yield) without non-physical fitting parameters. In the last decade, research into developing unconfined aquifer test solutions has mostly focused on explicitly coupling the aquifer with the linearized vadose zone. Despite the many advanced solution methods available, there still exists a need for realism to accurately simulate real-world aquifer tests.
The Effects of Ocean Acidity and Elevated Temperature on Bacterioplankton Community Structure and Metabolism  [PDF]
Nam Siu, Jude K. Apple, Craig L. Moyer
Open Journal of Ecology (OJE) , 2014, DOI: 10.4236/oje.2014.48038
Abstract:

By the end of the 21st century, mean sea surface temperatures are expected to increase 4?C, while atmospheric CO2 concentrations are predicted to triple causing seawater to become acidic. These compounding effects will undoubtedly have major consequences for the organisms and processes in the oceans. Bacterioplankton play a vital role in the marine carbon cycle and the oceans’ ability to sequester CO2. We utilized pCO2 perturbation experiments to investigate the effects of ocean acidity and elevated temperature on bacterioplankton community structure and metabolism. Terminal-restriction fragment length polymorphism (T-RFLP) of small subunit ribosomal (SSU) genes revealed that bacterioplankton incubated in lower pH conditions exhibited a reduction of species richness, evenness, and overall diversity, relative to those incubated in ambient pH conditions. Non-metric multidimensional scaling (MDS) of T-RFLP data resulted in clustering by pH suggesting that pH influenced the structure of these communities. Shifts in the dominant members of bacterioplankton communities incubated under different pH were observed in both T-RFLP and SSU clone library analyses. Both ambient and low pH communities were dominated by Gammaproteobacteria and Alphaproteobacteria, although abundance of Alphaproteobacteria increased in communities incubated at lower pH. This was expressed by the gamma to alpha ratio dropping from ~9 to 4, respectively. In general, the representative taxa from these two classes were distinctly different between the treatments, with a few taxa found to be persistent in both treatments. Changes in

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