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11.
Nabin Rayamajhi Byeong Yeal Jung Seung Bin Cha Min Kyung Shin Aeran Kim Min Su Kang Kang Mu Lee Han Sang Yoo 《Applied and environmental microbiology》2010,76(14):4760-4764
Fifteen nonrepetitive ampicillin-resistant Salmonella spp. were identified among 91 Salmonella sp. isolates during nationwide surveillance of Salmonella in waste from 131 chicken farms during 2006 and 2007. Additional phenotyping and genetic characterization of these 15 isolates by using indicator cephalosporins demonstrated that resistance to ampicillin and reduced susceptibility to cefoxitin in three isolates was caused by TEM-1 and DHA-1 β-lactamases. Plasmid profiling and Southern blot analysis of these three DHA-1-positive Salmonella serovar Indiana isolates and previously reported unrelated clinical isolates of DHA-1-positive Salmonella serovar Montevideo, Klebsiella pneumoniae, and Escherichia coli from humans and swine indicated the involvement of the large-size plasmid. Restriction enzyme digestion of the plasmids from the transconjugants showed variable restriction patterns except for the two Salmonella serovar Indiana isolates identified in this study. To the best of our knowledge, this is the first report of the presence of the DHA-1 gene among Salmonella spp. of animal origin.Nontyphoidal Salmonella (NTS) strains are a significant cause of gastrointestinal infections of food origin. These microbes are a heterogeneous group of medically important Gram-negative bacteria and can infect a wide range of animals, including humans (3, 6, 9-11, 25).Currently, no antimicrobial therapies are recommended for the treatment of NTS infection unless a patient is of extreme age, has an underlying disease, or is infected with an invasive Salmonella sp. However, the use of antibiotics in treatment of clinical enteric infection has been heavily compromised by emerging multidrug-resistant microbes (4, 17, 18, 23). In particular, resistance due to extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases is of special concern as these enzymes confer resistance to some of the front-line antibiotics used to treat enteric infection in humans and animals (4, 13, 14, 19).Four classes of β-lactamases are known to confer resistance to β-lactam antibiotics. Among these, plasmid-mediated class A and class C β-lactamases have been frequently reported, whereas class B and class D β-lactamases are relatively rare (4). TEM and SHV enzymes of class A β-lactamases are generally found in Gram-negative bacteria and are derived by one or more amino acid substitutions around the active site of the enzyme that is responsible for the ESBL phenotype (4). Recently, the CTX-M enzyme of class A β-lactamases has been increasingly reported from enteric microbes, like Salmonella and Escherichia coli (4, 5, 9, 15). These have greater activity against cefotaxime than do other oxyimino-β-lactam substrates, like ceftazidime, ceftriaxone, or cefepime (4, 5). Plasmid-mediated AmpC β-lactamases, like DHA and CMY, are not inhibited by clavulanic acid and have been isolated from a wide variety of clinical and community-acquired microbes (2, 4, 13, 14, 16). These β-lactamases are native to the chromosomes of many Gram-negative bacilli but are missing in some genera, like Salmonella (4). The majority of β-lactamases reported in Salmonella to date have been derived from human clinical isolates, and only limited information is available regarding Salmonella spp. derived from farm animals, although isolates from both humans and animals are of clinical and epidemiological importance (4, 15, 25).In light of this knowledge gap, our study focused on assessing the distribution of Salmonella serovars in poultry farms in South Korea. Subsequently, isolates were analyzed for resistance to antibiotics commonly used in farms. Phenotypic and genetic characteristics of ampicillin-resistant Salmonella isolates were tested to gain insight into what β-lactamases were prevalent among these strains. We also characterized DHA-1-associated plasmids in these Salmonella spp. and compared them with clinical isolates of Salmonella, Klebsiella pneumoniae, and Escherichia coli from humans and from swine. 相似文献
12.
Ajit Rayamajhi Sam Nightingale Nisha Keshary Bhatta Rupa Singh Elizabeth Ledger Krishna Prasad Bista Penny Lewthwaite Chandeshwar Mahaseth Lance Turtle Jaimie Sue Robinson Sareen Elizabeth Galbraith Malgorzata Wnek Barbara Wilmot Johnson Brian Faragher Michael John Griffiths Tom Solomon 《PloS one》2015,10(4)
Background
Japanese encephalitis (JE) virus (JEV) is a mosquito-borne flavivirus found across Asia that is closely related to West Nile virus. There is no known antiviral treatment for any flavivirus. Results from in vitro studies and animal models suggest intravenous immunoglobulin (IVIG) containing virus-specific neutralizing antibody may be effective in improving outcome in viral encephalitis. IVIG’s anti-inflammatory properties may also be beneficial.Methodology/Principal Findings
We performed a pilot feasibility randomized double-blind placebo-controlled trial of IVIG containing anti-JEV neutralizing antibody (ImmunoRel, 400mg/kg/day for 5 days) in children with suspected JE at two sites in Nepal; we also examined the effect on serum neutralizing antibody titre and cytokine profiles. 22 children were recruited, 13 of whom had confirmed JE; 11 received IVIG and 11 placebo, with no protocol violations. One child (IVIG group) died during treatment and two (placebo) subsequently following hospital discharge. Overall, there was no difference in outcome between treatment groups at discharge or follow up. Passive transfer of anti-JEV antibody was seen in JEV negative children. JEV positive children treated with IVIG had JEV-specific neutralizing antibody titres approximately 16 times higher than those treated with placebo (p=0.2), which was more than could be explained by passive transfer alone. IL-4 and IL-6 were higher in the IVIG group.Conclusions/Significance
A trial of IVIG for JE in Nepal is feasible. IVIG may augment the development of neutralizing antibodies in JEV positive patients. IVIG appears an appealing option for JE treatment that warrants further study.Trial Registration
ClinicalTrials.gov NCT01856205 相似文献13.
Rayamajhi N Cha SB Shin SW Jung BY Lim SK Yoo HS 《Applied and environmental microbiology》2011,77(9):3163-3166
In this study, we focused on determining the distribution and prevalence of major plasmid replicons in β-lactam-resistant Escherichia fergusonii and Enterobacteriaceae of animal and human origin. A high degree of plasmid variability and multiple plasmid replicons were observed among the isolates. The IncF and IncI1 replicons were the most prevalent in E. fergusonii and Salmonella enterica serovar Indiana isolated from swine and poultry in South Korea, respectively. The presence of broad-host-range plasmid replicons such as IncN, IncA/C, IncHI1, and IncHI2 that are associated with important virulence genes and toxins as well as antimicrobial resistance determinants indicates that E. fergusonii has the potential to become an important pig pathogen and possible emerging opportunistic zoonotic pathogen. 相似文献
14.
Paul D. Pratt Susan A. Wright Jeffrey R. Makinson Matthew F. Purcell Ted D. Center Min B. Rayamajhi 《Biocontrol Science and Technology》2014,24(10):1188-1191
Rhodomyrtus tomentosa is an invasive weed in Florida and Hawaii, USA. Host range testing indicates that the stem-mining lepidopteran Metharmostis multilineata, collected from Hong Kong, China aggressively feeds and completes development on R. tomentosa as well as New World species in three other genera. The unsuitability of M. multilineata as a biological control agent and details of the newly described species' biology are addressed. 相似文献
15.
Paul D. Pratt Min B. Rayamajhi Bradley Brown Matthew F. Purcell Ted D. Center 《Biocontrol Science and Technology》2014,24(9):1073-1076
The gall-producing midge Lophodiplosis trifida Gagné (Diptera: Cecidomyiidae) is an established biological control agent of the exotic tree Melaleuca quinquenervia (Cav.) Blake, which invades wetland systems of Florida (USA). Host use patterns within the tree canopy were investigated. Plant height affected within-plant distribution of galls as L. trifida attack rates were greater in lower versus higher portions of the M. quinquenervia canopy. Nonetheless, galls occurred even at tree-top levels of 13 m. 相似文献
16.
Paul D. Pratt Min B. Rayamajhi Thai K. Van Ted D. Center 《Biocontrol Science and Technology》2004,14(1):51-62
The Australian snout beetle, Oxyops vitiosa, was introduced to south Florida, USA, as a biological control agent of the invasive tree Melaleuca quinquenervia during the spring of 1997. As part of ongoing post-release evaluations of this weevil, we sought to quantify the population density that can be maintained by O. vitiosa larvae when fully exploiting the available melaleuca foliage. Seasonal population densities were modeled as a function of tree size distribution and density, plant phenology, quantity of acceptable foliage (suitable for larval development) and larval consumption values. Larval densities varied dramatically due to fluctuating resource availability and ranged from 830 946 larvae/ha in July–August to >4.5 million larvae/ha in January–February. The expected population density for a generalized (mixed sized) tree distribution was estimated to be 13.9 million larvae/ha. Larval densities increased to 18.8 million larvae/ha per year when large trees (>20 cm diameter at breast height) represented the dominant size class, whereas habitats dominated by medium (10–19 cm) and small (1.3–9 cm) trees were predicted to have larval densities of 11.3 and 6.3 million/year, respectively. Validation data obtained from smaller, more accessible plants suggested that the model overestimated realized yearly larval densities by 9% or 15 416 larvae/ha per year. 相似文献
17.
Angel G Rivera-Coln Niraj Rayamajhi Bushra Fazal Minhas Giovanni Madrigal Kevin T Bilyk Veronica Yoon Mathias Hüne Susan Gregory C H Christina Cheng Julian M Catchen 《Molecular biology and evolution》2023,40(3)
White-blooded Antarctic icefishes, a family within the adaptive radiation of Antarctic notothenioid fishes, are an example of extreme biological specialization to both the chronic cold of the Southern Ocean and life without hemoglobin. As a result, icefishes display derived physiology that limits them to the cold and highly oxygenated Antarctic waters. Against these constraints, remarkably one species, the pike icefish Champsocephalus esox, successfully colonized temperate South American waters. To study the genetic mechanisms underlying secondarily temperate adaptation in icefishes, we generated chromosome-level genome assemblies of both C. esox and its Antarctic sister species, Champsocephalus gunnari. The C. esox genome is similar in structure and organization to that of its Antarctic congener; however, we observe evidence of chromosomal rearrangements coinciding with regions of elevated genetic divergence in pike icefish populations. We also find several key biological pathways under selection, including genes related to mitochondria and vision, highlighting candidates behind temperate adaptation in C. esox. Substantial antifreeze glycoprotein (AFGP) pseudogenization has occurred in the pike icefish, likely due to relaxed selection following ancestral escape from Antarctica. The canonical AFGP locus organization is conserved in C. esox and C. gunnari, but both show a translocation of two AFGP copies to a separate locus, previously unobserved in cryonotothenioids. Altogether, the study of this secondarily temperate species provides an insight into the mechanisms underlying adaptation to ecologically disparate environments in this otherwise highly specialized group. 相似文献
18.
Endemic, obligate outcrossing plant species with narrow geographic distributions and disjunct populations are prone to loss of genetic diversity. Simultaneously, delineating clear species boundaries is important for targeted conservation efforts. The rare and endemic cactus, Sclerocactus brevihamatus subsp. tobuschii (SBT), has a parapatric relationship with Sclerocactus brevihamatus subsp. brevihamatus (SBB) but genetic distance between the two taxa is unknown. We: (1) developed taxon-specific polymorphic microsatellites, (2) assessed genetic diversity within and among nine populations of SBT, and within one population of SBB, and (3) estimated the genetic relationship between the two subspecies. Within-population genetic diversity of SBT was moderate to high (mean Ho?=?0.37; mean He?=?0.59). Indirect estimate of inbreeding corrected for null alleles (Fis-INEst) was low for SBT, ranging from 0.03 to 0.14 (mean Fis-INEst?=?0.07). Genetic differentiation among populations of SBT was low based on Fst (0.08) and AMOVA (ФPT?=?0.10). Lack of genetic and spatial correlation in SBT populations coupled with the presence of private alleles and bottleneck events in several populations suggests that reproductive isolation is occurring but that sufficient time may not have yet passed to manifest strong differentiation. Cluster analyses segregated the 10 populations into three distinct groups, and separated SBB genotypes clearly. Results suggest that while hybridization between the two subspecies may occur, SBT is clearly differentiated genetically from SBB to retain its current taxonomic status. 相似文献
19.
Ellen C. Lake Melissa C. Smith Min B. Rayamajhi Paul D. Pratt F. Allen Dray Jr 《Biocontrol Science and Technology》2018,28(6):603-613
The successful establishment or failure of a new population is often attributed to propagule pressure, the combination of the number of independent introduction events, and the number of individuals released at each event. The design of optimal release strategies for biological control agents benefits from an understanding of the impact of propagule pressure on the species being released. The dispersal rate of individuals from nascent population foci can also affect establishment success. We assessed the minimum threshold for establishment and measured dispersal of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent for Dioscorea bulbifera (Dioscoreales), air potato. Replicated releases of 10, 50, and 100 adults of L. cheni were conducted on the east and west coasts of south Florida. Dispersal was measured from 19 of these sites plus 19 additional release locations in south and central Florida. Lilioceris cheni established populations from all three release sizes with no apparent influence of site location. Releases of 10, 50, and 100 adults resulted in 50%, 67%, and 85% establishment, respectively. Beetles dispersed an average of 1.41?±?0.515?km/yr. Dispersal distance was significantly affected by the time since release but not the number of individuals released. Our results suggest that future releases of 100 individuals could be spaced several kilometres apart on the landscape to facilitate rapid colonisation of D. bulbifera infestations. 相似文献
20.
Michael J. Griffiths Jennifer V. Lemon Ajit Rayamajhi Prakash Poudel Pramina Shrestha Vijay Srivastav Rachel Kneen Antonieta Medina-Lara Rupa R. Singh Tom Solomon 《PLoS neglected tropical diseases》2013,7(9)