共查询到20条相似文献,搜索用时 31 毫秒
1.
Lucia Rizzotti Federica La Gioia Franco Dellaglio Sandra Torriani 《Antonie van Leeuwenhoek》2009,96(1):43-52
In the present study, 20 enterococci belonging to the species Enterococcus faecalis (12 strains), Enterococcus faecium (4), Enterococcus durans (2), Enterococcus hirae (1) and Enterococcus mundtii (1) and originating from a total production chain of swine meat commodities were analysed to investigate the diversity of
their tetracycline resistance gene tet(M). PCR–RFLP and sequence analysis showed that the tet(M) gene of most strains can be correlated with the Tn916 transposon. Conversely, tet(M) of six E. faecalis and the E. hirae strain, all isolated from pig faecal samples, may be associated with previously undescribed members of the Tn916-1545 transposon family. In vitro filter conjugation trials showed the ability of 50% of the enterococcal strains, including E. mundtii, to transfer the tet(M) gene (and the associated Tn916 and new transposons) to E. faecalis or Listeria innocua recipient strains. tet(M) gene transfer to L. innocua recipient was also directly observed in meat food products. Collectively, these sequence and conjugation data indicate that
various transposons can be responsible of the spread of tetracycline resistance in enterococci and validate the opinion that
Enterococcus species are important sources of antibiotic resistance genes for potentially pathogenic bacteria occurring in the food chain.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
The house fly (Musca domestica L.) alimentary canal was evaluated for the potential of horizontal transfer of tetM on plasmid pCF10 among Enterococcus faecalis. Two sets of experiments were conducted: (1) house flies without surface sterilization and (2) surface-sterilized flies.
Both sets of flies were exposed to E. faecalis OG1RF:pCF10 as donor for 12 h and then E. faecalis OG1SSp as recipient for 1 h. Another group of flies received the recipient first for 12 h followed by exposure to the donor
strain for 1 h. House flies were screened daily to determine the donor, recipient, and transconjugant bacterial load for up
to 5 days. In addition, the sponge-like mouth parts used for food uptake (labellum) of surface-sterilized house flies were
removed and analyzed for donors, recipients, and transconjugants, separately. In both groups of flies (n = 90 flies/group), transfer occurred within 24 h after exposure with a transconjugant/donor rate from 8.6 × 10−5 to 4.5 × 101. Transconjugants were also isolated from the house fly labellum. Our data suggest that the house fly digestive tract provides
a suitable environment for horizontal transfer of conjugative plasmids and antibiotic resistance genes among enterococci.
Our results emphasize the importance of this insect as a potential vector of antibiotic-resistant bacterial strains. 相似文献
3.
Faezi Ghasemi Mohammad Tayeri Alireza 《World journal of microbiology & biotechnology》2007,23(9):1327-1332
Sixteen aerobic endospore-forming Bacillus spp. were isolated from fully fermented tea leaf samples from 10 tea factories in Lahijan and Langrod cities (Gillan province,
Iran). Bacillus spp. isolates were characterized using phenotypic characteristics, antibiotic susceptibility and cellular fatty acid (CFA)
patterns. Based on the data obtained, five isolates of tea Bacillus spp. (TB): TB2, TB4, TB6, TB10 and TB12 belonged to the species B. subtilis. Two isolates, TB1 and TB14 were recognized as B.
licheniformis. Two Bacillus spp. isolates, TB9 and TB 16 were identified as B. sphaericus. Two isolates, TB5 and TB13 were shown to be B. pumilus. Two isolates, TB7 and TB15 belonged to B. cereus. Amongst the isolates, Bacillus sp. TB3, Bacillus sp. TB8 and Bacillus sp. TB11 showed different phenotypic traits, distinct antibiotic sensitivity and fatty acid profiles, and they may represent
novel species. The isolates showed polyphenol oxidase (tyrosinase) and peroxidase activities. The highest polyphenol oxidase
and peroxidase activities were observed for Bacillus sp. TB3 and B. licheniformis TB14, respectively, where values of 5.48 and 3.73 units mL−1 were observed. 相似文献
4.
Yanfeng Tuo Lanwei Zhang Xue Han Ming Du Yingchun Zhang Huaxi Yi Weiqin Zhang Yuehua Jiao 《World journal of microbiology & biotechnology》2011,27(3):505-511
The objective of this study was to evaluate the in vitro immunomodulating capacity of Lactobacillus
coryniformis subsp torquens T3L (L.
coryniformis T3L) isolated from traditional fermented yak’s milk in Tibet, China, and Lactobacillus paracasei supsp. paracasei M5L (L. paracasei M5L)isolated from kumiss in Sinkiang, China was used as control. The effects of live bacteria, cell wall and genomic DNA
of the two Lactobacillus strains on human peripheral blood mononuclear cells (PBMCs) proliferation, production of interleukin-12 (IL-12 p70), interferon
gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), and natural killer (NK) cell activity were assessed. The live bacteria,
cell wall and genomic DNA of the two lactobacilli exerted proliferative effects on PBMCs. Live bacteria at 1 × 106 c.f.u. ml−1, cell wall at 20 μg protein ml−1 and DNA at 50 μg DNA ml−1 of the strainS induced the secretion of IL-12 (p70), IFN-γ and TNF-α by PBMCs. NK cell activities increased after cultivation
of PBMCs with live bacteria, cell wall and DNA of the strains. Overall, these results demonstrate that the live bacteria,
cell wall and genomic DNA of the two Lactobacillus strains exhibit immunomodulating activity. 相似文献
5.
Bacteria of the genus Vibrio are an important component of marine ecosystems worldwide. The genus harbors several human pathogens, for instance the species
Vibrio parahaemolyticus, a main cause for foodborne gastroenteritis in Asia and the USA. Pathogenic V. parahaemolyticus strains emerged also in Europe, but little is known about the abundance, pathogenicity and ecology of V. parahaemolyticus especially in Northern European waters. This study focuses on V. parahaemolyticus and its close relative Vibrio alginolyticus in the North Sea (Helgoland Roads, Germany). Free-living, plankton-attached and shellfish-associated Vibrio spp. were quantified between May 2008 and January 2010. CFUs up to 4.3 × 103 N l−1 and MPNs up to 240 N g−1 were determined. Phylogenetic classification based on rpoB gene sequencing revealed V. alginolyticus as the dominant Vibrio species at Helgoland Roads, followed by V. parahaemolyticus. We investigated the intraspecific diversity of V. parahaemolyticus and V. alginolyticus using ERIC-PCR. The fingerprinting disclosed three distinct groups at Helgoland Roads, representing V. parahaemolyticus, V. alginolyticus and one group in between. The species V. parahaemolyticus occurred mainly in summer months. None of the strains carried the virulence-associated genes tdh or trh. We further analyzed the influence of nutrients, secchi depth, temperature, salinity, chlorophyll a and phytoplankton on
the abundance of Vibrio spp. and the population structure of V. parahaemolyticus. Spearman Rank analysis revealed that particularly temperature correlated significantly with Vibrio spp. numbers. Based on multivariate statistical analyses we report that the V. parahaemolyticus population was structured by a complex combination of environmental parameters. To further investigate these influences is
the key to understanding the dynamics of Vibrio spp. in temperate European waters, where this microbial group and especially the pathogenic species, are likely to gain in
importance. 相似文献
6.
Ping Su Anders Henriksson Christina Nilsson Hazel Mitchell 《World journal of microbiology & biotechnology》2008,24(9):1837-1842
The aim of this study was to assess the effect of a commercial green tea extract (TEAVIGO™) on the microbial growth of three
probiotic strains (Lactobacillus and Bifidobacterium), as well as three pathogenic bacteria. MIC and co-culture studies were performed. The MICs of the green tea extract against
Staphylococcus aureus and Streptococcus pyogenes (100 μg ml−1) were considerably lower than those against the probiotic strains tested (>800 μg ml−1) and Escherichia coli (800 μg ml−1). In co-culture studies, a synergistic effect of the probiotic strains and the green tea extract was observed against both
Staph. aureus and Strep. pyogenes. Green tea extract in combination with probiotics significantly reduced the viable count of both pathogens at 4 h and by
24 h had completely abolished the recovery of viable Staph. aureus and Strep. pyogenes. These reductions were more significant than the reductions induced by probiotics or green tea extracts used separately.
These results demonstrate the potential for combined therapy using the green tea extract plus probiotics on microbial infections
caused by Staph. aureus and Strep. pyogenes. As probiotics and the green tea extract are derived from natural products, treatment with these agents may represent important
adjuncts to, or alternatives to, conventional antibiotic therapy. 相似文献
7.
Francesca Borgo Giovanni Ricci Karsten Arends Katarzyna Schiwon Elisabeth Grohmann Maria Grazia Fortina 《Current microbiology》2009,59(3):261-266
Five Enterococcus italicus strains harbouring tet genes responsible for the tetracycline resistance were subjected to plasmid profile determination studies. For four strains
tested the profiles showed between three and six plasmid bands, the size of which ranged between 1.6 and 18.5 kb. Southern
hybridization experiments associated tetS and tetK genes with chromosomal DNA in all strains and tetM gene with plasmids of around the same size (18.5 kb) in two of the tested strains. The ability of the new species to transfer
tetM gene was studied by transfer experiments with the tetracycline-susceptible recipient strains E. faecalis JH2-2 and OG1RF; mobilization experiments were performed with E. faecalis JH 2-2 harbouring the conjugative plasmid pIP501as helper plasmid. The results obtained show that the new enterococcal species
was able to acquire antibiotic resistance by conjugation, but not to transfer its plasmids to other bacteria. Further PCR
and hybridization experiments carried out to assess the presence of mobilization sequences also suggest that the tetM plasmid from E. italicus is a non-mobilizable plasmid. 相似文献
8.
L. I. Vorob’yova A. V. Fedotova E. Yu. Khodzhaev 《Applied Biochemistry and Microbiology》2010,46(6):567-573
Reactivating factor (RF) from Luteococcus japonicus subsp. casei had a protective action on UV-irradiated cells of Escherichia coli AB1157 with a native reparation system and on cells of isogenic reparation mutants of E. coli UvrA−, RecA−, and PolA−: the effect resulted in multifold increase of survivability. Defense action of L. casei exometabolite is not connected with stimulating reparation systems in E. coli, and, probably, it is mediated by involvement of the exometabolite in the mechanism of cell division. RF did not provoke
the reactivation of E. coli cells inactivated by UV-light. 相似文献
9.
Oberbeckmann S Fuchs BM Meiners M Wichels A Wiltshire KH Gerdts G 《Microbial ecology》2012,63(3):543-551
Vibrio species are ubiquitously distributed in marine waters all over the world. High genome plasticity due to frequent mutation,
recombination, and lateral gene transfer enables Vibrio to adapt rapidly to environmental changes. The genus Vibrio comprises several human pathogens, which commonly cause outbreaks of severe diarrhea in tropical regions. In recent years,
pathogenic Vibrio emerged also in coastal European waters. Little is known about factors driving the proliferation of Vibrio spp. in temperate waters such as the North Sea. In this study a quantification of Vibrio in the North Sea and their response to biotic and abiotic parameters were assessed. Between January and December 2009, Vibrio at Helgoland Roads (North Sea, Germany) were quantified using fluorescence in situ hybridization. Vibrio numbers up to 3.4 × 104 cells × mL−1 (2.2% of total microbial counts) were determined in summer, but their abundance was significantly lower in winter (5 × 102 cells × mL−1). Correlations between Vibrio and nutrients (SiO2, PO4
3−, DIN), Secchi depth, temperature, salinity, and chlorophyll a were calculated using Spearman rank analysis. Multiple stepwise
regression analysis was carried out to analyze the additive influence of multiple factors on Vibrio. Based on these calculations, we found that high water temperature and low salinity best explained the increase of Vibrio cell numbers. Other environmental parameters, especially nutrients and chlorophyll a, also had an influence. All variables
were shown to be subject to the overall seasonal dynamics at Helgoland Roads. Multiple regression models could represent an
efficient and reliable tool to predict Vibrio abundances in response to the climate change in European waters. 相似文献
10.
11.
Gaoge Wang Li Shuai Yun Li Wei Lin Xiaowei Zhao Delin Duan 《Journal of applied phycology》2008,20(4):403-409
During an occurrence of Hole-Rotten Disease of Laminaria japonica in a cultivating farm in Ma Shan Shandong province, China, 42 Gram-negative epiphytic marine bacteria were isolated and purified
on Zobell 2216E marine agar medium. Morphological and biochemical characteristics of each isolated bacterium were studied,
and molecular identification of bacterial strains was conducted with polymerase chain reaction amplification to 16S rRNA gene
sequence analysis. Based on nearly full length of 16S rRNA gene sequence analysis, the isolated strains were bacteria that
belong to genus Pseudoalteromonas, Vibrio, Halomonas and Bacillus. The percentage of each group was 61.9%, 28.6%, 7.1% and 2.4% respectively. The results of pathogenicity assay showed that
12 strains could cause the disease symptoms in sporophytes of L. japonica. They belonged to the genera Pseudoalteromonas, Vibrio and Halomonas with 58.3%, 33.3%, 8.3% respectively. The results suggest that these bacteria are the dominant marine bacteria on diseased
sporophytes of L. japonica and may be the potential pathogenic bacteria associated with Hole-Rotten Disease of L. japonica. 相似文献
12.
Bacillus
thuringiensis subsp. kurstaki BUPM255 secretes a chitobiosidase Chi255 having an expected molecular weight of 70.665 kDa. When the corresponding gene,
chi255, was expressed in E. coli, the active form, extracted from the periplasmic fraction of E. coli/pBADchi255, was of about 54 kDa, which suggested that Chi255 was excessively degraded by the action of E. coli proteases. Therefore, in vitro progressive C-terminal Chi255 deleted derivatives were constructed in order to study their
stability and their activity in E. coli. Interestingly, when the chitin binding domain (CBD) was deleted from Chi255, an active form (Chi2555Δ5) of expected size
of about 60 kDa was extracted from the E. coli periplasmic fraction, without the observation of any proteolytic degradation. Compared to Chi255, Chi255Δ5 exhibited a higher
chitinase activity on colloidal chitin. Both of the enzymes exhibit activities at broad pH and temperature ranges with maximal
enzyme activities at pH 5 and pH 6 and at temperatures 50°C and 40°C, respectively for Chi255 and Chi255Δ5. Thus, it was concluded
that the C-terminal deletion of Chi255 CBD might be a nice tool for avoiding the excessive chitinase degradation, observed
in the native chitinase, and for improving its activity. 相似文献
13.
We previously demonstrated efficient transformation of the thermophile Geobacillus kaustophilus HTA426 using conjugative plasmid transfer from Escherichia coli BR408. To evaluate the versatility of this approach to thermophile transformation, this study examined genetic transformation of various thermophilic Bacillus and Geobacillus spp. using conjugative plasmid transfer from E. coli strains. E. coli BR408 successfully transferred the E. coli–Geobacillus shuttle plasmid pUCG18T to 16 of 18 thermophiles with transformation efficiencies between 4.1 × 10?7 and 3.8 × 10?2/recipient. Other E. coli strains that are different from E. coli BR408 in intracellular DNA methylation also generated transformants from 9 to 15 of the 18 thermophiles, including one that E. coli BR408 could not transform, although the transformation efficiencies of these strains were generally lower than those of E. coli BR408. The conjugation was performed by simple incubation of an E. coli donor and a thermophile recipient without optimization of experimental conditions. Moreover, thermophile transformants were distinguished from abundant E. coli donor only by high temperature incubation. These observations suggest that conjugative plasmid transfer, particularly using E. coli BR408, is a facile and versatile approach for plasmid introduction into thermophilic Bacillus and Geobacillus spp., and potentially a variety of other thermophiles. 相似文献
14.
Ronghua Qian Zhaohua Xiao Chongwen Zhang Wuying Chu Zhijuan Mao Lian Yu 《World journal of microbiology & biotechnology》2008,24(2):245-251
Vibrio alginolyticus, a Gram-negative bacterium, is one of Vibrio pathogens common to human and marine animals. Outer membrane proteins of bacteria play an important role during infection
and induction of host immune response. In present research, two outer membrane protein genes (OmpK and OmpW) of V. alginolyticus were cloned and expressed. The open reading frames of OmpK and OmpW contain 846 bp and 645 bp, respectively, the mature proteins consist of 261 and 193 amino acid residues. At the signal peptides
positions −3 to −1, the amino acids were V-M-A in OmpK and V-F-A in OmpW, which consistented with the observed sequence V-X-A of the signal peptides of transmembrane OMP. The alignment analysis
indicated that both proteins were highly conserved, which could serve as surface antigens for vaccine candidates. SDS-PAGE
indicated two genes over-expressed in E. coli BL21 (DE3). By affinity chromatography on Ni2+-nitriloaceate resin, the recombinant proteins were purified from inclusion bodies. Western blot analysis revealed that both
proteins had immunoreactivity, which provided a base for further study on the evaluation of diagnostication and vaccine candidates. 相似文献
15.
T. Zhang 《In vitro cellular & developmental biology. Plant》2007,43(2):91-94
This study investigated the factors affecting in vitro flowering of Perilla frutescens. The shoots regenerated from cotyledonary and hypocotyl explants cultured on Murashige and Skoog (MS) medium supplemented
with benzyladenine (BA) and indole-3-acetic acid, each at 0.5 mg l−1, were excised and transferred to MS medium containing 30 g l−1 of sucrose, 8.25 g l−1 of ammonium nitrate, and 1.0 mg l−1 of BA. After 40 d of culture, 86.2% of shoots flowered and most of which self-fertilized in vitro and produced mature fruits with viable seeds. These seeds were germinated and plants were grown to maturity and flowered
in soil under greenhouse conditions. The in vitro flowering system reported in this study may facilitate rapid breeding of P. frutescens and offers a model system for studying the physiological mechanism of flowering. 相似文献
16.
Forty-eight isolates resistant to at least two antibiotics were selected from 53 antibiotic-resistant enterococci from chicken
and pig meat and faeces and analysed for specific resistance determinants. Of the 48 multidrug-resistant (MDR) strains, 31
were resistant to two antibiotics (29 to erythromycin and tetracycline, 1 to erythromycin and vancomycin, 1 to vancomycin
and tetracycline), 14 to three (erythromycin, tetracycline and vancomycin or ampicillin) and 3 to four (erythromycin, vancomycin,
ampicillin and gentamicin). erm(B), tet(M), vanA and aac (6′)-Ie aph (2′′)-Ia were the antibiotic resistance genes most frequently detected. All 48 MDR enterococci were susceptible to linezolid and daptomycin.
Enterococcus faecalis (16), Enterococcus faecium (8), Enterococcus mundtii (2) and Enterococcus gallinarum (1) were identified in meat, and E. faecium (13) and Enterococcus durans (13) in faeces. Clonal spread was not detected, suggesting a large role of gene transfer in the dissemination of antibiotic
resistance. Conjugative transfer of resistance genes was more successful when donors were enterococcal strains isolated from
faeces; co-transfer of vanA and erm(B) to a human E. faecium occurred from both E. faecium and E. durans pig faecal strains. These data show that multidrug resistance can be found in food and animal species other than E. faecium and E. faecalis, and that these species can efficiently transfer antibiotic resistance to human strains in inter-specific matings. In particular,
the occurrence of MDR E. durans in the animal reservoir could have a role in the emergence of human enterococcal infections difficult to eradicate with antibiotics. 相似文献
17.
Rangaraj Nandakumar Li Chen Suzanne M. D. Rogers 《In vitro cellular & developmental biology. Plant》2007,43(3):187-194
A highly reproducible Agrobacterium-mediated transformation system was developed for the wetland monocot Juncus accuminatus. Three Agrobacterium tumefaciens binary plasmid vectors, LBA4404/pTOK233, EHA105/pCAMBIA1201, and EHA105/pCAMBIA1301 were used. All vectors contained the
35SCaMV promoter driven, intron containing, β-glucuronidase (gus), and hygromycin phosphotransferase (hptII) genes within their T-DNA. After 48 h of cocultivation, 21-d-old seedling derived calli were placed on medium containing
timentin at 400 mg l−1, to eliminate the bacteria. Calli were selected on MS medium containing 40 or 80 mg l−1 hygromycin, for 3 mo. Resistant calli were regenerated and rooted on MS medium containing hygromycin, 5 mg l−1(22.2 μM) of 6-benzylamino-purine (BA) and 0.1 mg l−1(0.54 μM) of alpha-naphthaleneacetic acid (NAA), respectively. Seventy-one transgenic cell culture lines were obtained and
39 plant lines were established in the greenhouse. All the plants were fertile, phenotypically normal, and set viable seed.
Both transient and stable expression of the gus gene were demonstrated by histochemical GUS assays of resistant calli, transgenic leaf, root, inflorescence, seeds, and whole
plants. The integration of gus and hptII genes were confirmed by polymerase chain reaction (PCR) and Southern analysis of both F0 and F1 progenies. The integrated genes segregated to the subsequent generation in Mendelian pattern. To our knowledge, this is the
first report of the generation of transgenic J. accuminatus plants. 相似文献
18.
Ruixiang Zhao Junliang Sun Haizhen Mo Yang Zhu 《World journal of microbiology & biotechnology》2007,23(2):195-200
Metabolites from Lactobacillus acidophilus were analysed. The results showed that Lactobacillus
acidophilus Ind-1 and Lactobacillus acidophilus Lakcid produced respectively 12.73 g and 13.33 g lactic acid l−1 after incubating in skim milk at 37 °C for 36 h; and 2.229 unit and 1.808 unit β-galactosidase l−1 in an MRS medium. The proteolytic activity of Lactobacillus acidophilus was high and the content of 17 free amino acids in the fermented milk of Lactobacillus
acidophilus Ind-1 and Lactobacillus acidophilus Lakcid was 394.4 mg l−1 and 563.2 mg l−1, respectively. Meantime, Lactobacillus acidophilus reduced cholesterol level in an MRS medium supplemented with cholesterol. Furthermore, Lactobacillus
acidophilus Ind-1 and Lactobacillus acidophilus Lakcid showed antimicrobial activity against Bacillus anthracis and Escherichia coli. 相似文献
19.
Orlita A Sidwa-Gorycka M Malinski E Czerwicka M Kumirska J Golebiowski M Lojkowska E Stepnowski P 《Biotechnology letters》2008,30(3):541-545
Growth of Ruta graveolens shoots was induced when Bacillus sp. cell lysates were added to the culture medium. Elicitation of coumarin by this lysate was also very effective; the concentrations
of isopimpinelin, xanthotoxin and bergapten increased to 610, 2120 and 1460 μg g−1 dry wt, respectively. It also had a significant effect on the production of psoralen and rutamarin (680 and 380 μg g−1 dry wt) and induced the biosynthesis of chalepin, which was not detected in the control sample, up to 47 μg g−1 dry wt With lysates of the Pectobacterium
atrosepticum, their effect on growth was not so significant and had no effect on the induction of coumarin accumulation. But elicitation
with this lysate was much more effective for inducing the production of furoquinolone alkaloids; the concentrations of γ-fagarine,
skimmianine, dictamnine and kokusaginine rose to 99, 680, 172 and 480 μg g−1 dry wt, respectively. 相似文献
20.
de Niederhäusern S Bondi M Messi P Iseppi R Sabia C Manicardi G Anacarso I 《Current microbiology》2011,62(5):1363-1367
In last decade methicillin-resistant Staphylococcus aureus with high level of vancomycin-resistance (VRSA) have been reported and generally the patients with VRSA infection were also
infected with a vancomycin-resistant Enterococcus (VRE). Considering that the high level of vancomycin-resistance in VRSA isolates seems to involve the horizontal transfer
of Tn1546 transposon containing vanA gene from coinfecting VRE strains, the authors have studied the “in vitro” conjugative transfer of this resistance from VanA
enterococci to S. aureus. Out of 25 matings performed combining five vancomycin-resistant enterococci as donors (three Enterococcus faecalis and two Enterococcus faecium), and five S. aureus as recipients, all clinical isolates, two have been successful using E. faecalis as donor. The transfer of vancomycin-resistance was confirmed by vanA gene amplification in both transconjugants and the resistance was expressed at lower levels (MIC 32 μg/ml) in comparison
with the respective VRE donors (MIC > 128 μg/ml). The vancomycin-resistance of trasconjugants was maintained even after subsequent
overnight passages on MSA plates containing subinhibitory levels of vancomycin. This study shows that the vanA gene transfer can be achieved through techniques “in vitro” without the use of laboratory animals employed, in the only similar
experiment previously carried out by other authors, as substrate for the trasconjugant growth. Moreover, in that previous
experiment, contrary to this study, the vancomycin resistant S. aureus trasconjugants were selected on erythromycin agar and not by direct vancomycin agar selection. 相似文献