学生宿舍和食堂环境中克罗诺杆菌污染状况及分子分型和耐药特征分析

目的 了解徐州市某学校学生宿舍和食堂环境中克罗诺杆菌污染状况、分子分型及耐药特征,为预警食源性克罗诺杆菌病暴发提供参考.方法 采集徐州市某学校学生宿舍和食堂环境样品156份,分离并鉴定克罗诺杆菌,并利用基于O-抗原的血清分型和多位点序列分型(multilocus sequence typing,MLST)技术对分离株进...     

Genotypic and phenotypic virulence characteristics and antimicrobial resistance of Yersinia spp. isolated from meat and milk products

A total of 300 food samples including 180 milk and 120 meat products have been examined for the presence of Yersinia spp. using the ISO 10273 and the cold enrichment method. The overall prevalence of Yersinia spp. was 84 (28%). Yersinia enterocolitica was isolated from 18 (6%) of the 300 samples. The other Yersinia species were detected in the samples Yersinia rohdei 15 (5%), Yersinia intermedia 14 (4.7%), Yersinia pseudotuberculosis 12 (4%), Yersinia ruckeri 12 (4%), Yersinia mollaretii 5 (1.7%), Yersinia bercovieri 4 (1.3%), and atypical Yersinia spp. 4 (1.3%). The conventionally identified Y. enterocolitica strains were also confirmed by the 16S rRNA gene sequencing. All Y. enterocolitica strains biotyped as 1A had negative results in the phenotypic virulence tests. The 84 Yersinia strains were also examined genotypically for the presence of virulence genes. None of the Y. enterocolitica and other Yersinia strains contained the ail, ystA, yadA, and virF except only 1 Y. intermedia and 2 Y. enterocolitica strains that were found to be positive for ystB. Antimicrobial resistance of 84 Yersinia to 16 antimicrobial agents was determined by the disk diffusion method. All strains were sensitive to tobramycine and imipenem while resistant to clindamycin. Although 84.5% of the strains were resistant to at least 3 or more antimicrobial agents, 64.3% of them were resistant to 4 or more antimicrobial agents.     

底物和环境因子对鱼源腐败希瓦氏菌和假单胞菌生长动力学的影响

水产品在贮运和加工过程中极易腐败,微生物是引起腐败的主要原因,腐败希瓦氏菌和假单胞菌分别是低温有氧贮藏海水鱼和淡水鱼时的特定腐败菌.为探讨环境因子和底物对特定腐败菌的影响,以源自大黄鱼和罗非鱼中的腐败希瓦氏菌和假单胞菌为对象,探究不同底物、温度、pH和NaCl影响下的菌体生长动态,采用Gompertz方程拟合生长曲线,...     

Occurrence and Antimicrobial Susceptibility of Listeria monocytogenes Isolated from Brined White Cheese in Jordan

Listeria monocytogenes is a serious foodborne pathogen that has been isolated from different dairy food products. Several foodborne outbreaks of listeriosis have been associated with consumption of cheese. The aims of this study were to determine the occurrence of L. monocytogenes and Listeria spp. in brined white cheese (BWC) sold in Jordan, and to determine the susceptibility of isolated L. monocytogenes to antimicrobials. Three hundred and fifty samples of 5 different types of BWC (akkawi, boiled, halloumi, pasteurized, and shellal) were collected from a local market in Jordan. The ISO (11290-1) procedure was followed for isolation and identification of Listeria spp. from cheese samples and a polymerase chain reaction (PCR) technique was used for confirmation of L. monocytogenes isolates. The VITEK2 automated system was used for testing antimicrobial susceptibility of L. monocytogenes isolates. The overall prevalence of Listeria spp. in cheese sample was 27.1%. L. monocytogenes was isolated from 39 (11.1%) samples. Other isolated species were L. grayi (6.9%), L. innocua (2%), L. ivanovii (4%), L. seeligeri (2%), and L. welshimeri (0.3%). The pH values and salt concentrations of L. monocytogenes positive cheese samples ranged from 5.10 to 6.32 and 5.64 to 13.16, respectively. L. monocytogenes isolates were sensitive or intermediate susceptible to imipenem, gentamicin, linezolid, teicoplanin, vancomycin, fusidic acid, trimethoprim/sulfamethoxazole, benzylpenicillin, ciprofloxacin, erythromycin, tetracycline, and rifampicin, but resistant to fosfomycin, oxacillin, and clindamycin.     

大黄鱼中复合腐败菌腐败能力的分析

通过分析接种腐败菌的大黄鱼无菌鱼块在贮藏中的感官、腐败代谢产物和腐败菌的变化,以腐败菌生长动力学参数和腐败代谢产物产量因子(YTVB-N/CFU 和YTMA/CFU)为指标,探讨冷藏大黄鱼优势腐败菌(腐败希瓦氏菌、假单胞菌以及这两种菌的复合菌)的腐败能力。结果表明,接种腐败希瓦氏菌、假单胞菌和复合菌的无菌鱼块的货架期分别为168、174、168h,说明接种假单胞菌的货架期较长。腐败希瓦氏菌、假单胞菌和复合菌的YTVB-N/CFU 基本一致,腐败希瓦氏菌的YTMA/CFU 明显大于假单胞菌和复合菌,腐败希瓦氏菌的腐败能力较假单胞菌和复合菌强。假单胞菌对腐败希瓦氏菌的生长有一定的拮抗作用,但仅在较高数量时才有明显作用,腐败希瓦氏菌是有氧冷藏养殖大黄鱼的特定腐败菌。     

Factors associated with the likelihood of Giardia spp. and Cryptosporidium spp. in soil from dairy farms

A study was conducted to identify factors associated with the likelihood of detecting Giardia spp. and Cryptosporidium spp. in the soil of dairy farms in a watershed area. A total of 37 farms were visited, and 782 soil samples were collected from targeted areas on these farms. The samples were analyzed for the presence of Cryptosporidium spp. oocysts, Giardia spp. cysts, percent moisture content, and pH. Logistic regression analysis was used to identify risk factors associated with the likelihood of the presence of these organisms. The use of the land at the sampling site was associated with the likelihood of environmental contamination with Cryptosporidium spp. Barn cleaner equipment area and agricultural fields were associated with increased likelihood of environmental contamination with Cryptosporidium spp. The risk of environmental contamination decreased with the pH of the soil and with the score of the potential likelihood of Cryptosporidium spp. The size of the sampling site, as determined by the sampling design, in square feet, was associated nonlinearly with the risk of detecting Cryptosporidium spp. The likelihood of the Giardia cyst in the soil increased with the prevalence of Giardia spp. in animals (i.e., 18 to 39%). As the size of the farm increased, there was decreased risk of Giardia spp. in the soil, and sampling sites which were covered with brush or bare soil showed a decrease in likelihood of detecting Giardia spp. when compared to land which had managed grass. The number of cattle on the farm less than 6 mo of age was negatively associated with the risk of detecting Giardia spp. in the soil, and the percent moisture content was positively associated with the risk of detecting Giardia spp. Our study showed that these two protozoan exist in dairy farm soil at different rates, and this risk could be modified by manipulating the pH of the soil.     

食品中克罗诺杆菌分离菌株生物被膜形成、耐药性及毒力基因检测

研究食品中克罗诺杆菌分离菌株的生物被膜形成、耐药性以及携带毒力基因情况。在成都市周边农贸市场和路边小摊采集食品样品129份,采用DFI 阪崎肠杆菌显色培养基分离克罗诺杆菌;通过16S rRNA序列比对分析鉴定分离菌株;采用试管法和微孔板法分析菌株生物被膜形成能力,同时研究温度对细菌成膜能力影响;采用纸片法检测分离菌株对18种抗生素的耐药性;采用PCR方法检测分离菌株携带cpa、hly、sip 和ompX毒力基因情况。结果发现从129份食品样本中共检出克罗诺杆菌43株,检出率为33.3%。43株克罗诺杆菌食品分离菌株的成膜率为90.7%,并且温度对细菌成膜影响明显。四种毒力基因中,ompX检出率为100%;cpa检出率为13.9%;hly检出率为11.6%;sip基因未检出。耐药表型检测发现43株克罗诺杆菌食品分离菌株对青霉素、克林霉素、万古霉素、苯唑西林和杆菌肽B的耐药率为100%,对利福平的耐药率达97.7%;对红霉素的耐药率为7%;对环丙沙星、庆大霉素、四环素、氯霉素、亚胺培南、磺胺甲恶挫、呋喃妥因、头孢西丁、链霉素、阿米卡星、氧氟沙星等100%敏感。本研究表明克罗诺杆菌食品分离菌株具有较好的形成生物被膜能力,对常见的抗生素耐药率较高,并且分离菌株携带一定的毒力基因,对食品安全造成潜在威胁。     

Prevalence,antimicrobial susceptibility,and antibiotic resistance gene transfer of Bacillus strains isolated from pasteurized milk

Pasteurization is carried out in dairy industries to kill harmful bacteria present in raw milk. However, endospore-forming bacteria, such as Bacillus, cannot be completely eliminated by pasteurization. In this study, a total of 114 Bacillus strains were isolated from 133 pasteurized milk samples. Antibiotic susceptibility tests showed that the percentage of Bacillus with intrinsic resistance to ampicillin and penicillin were 80 and 86%, respectively. Meanwhile, some Bacillus isolates had acquired resistance, including trimethoprim-sulfamethoxazole resistance (10 isolates), clindamycin resistance (8 isolates), erythromycin resistance (2 isolates), and tetracycline resistance (1 isolate). To further locate these acquired resistance genes, the plasmids were investigated in these 16 Bacillus strains. The plasmid profile indicated that Bacillus cereus BA008, BA117, and BA119 harbored plasmids, respectively. Subsequently, the Illumina Novaseq PE150 was applied for the genomic and plasmid DNA sequencing. Notably, the gene tetL encoding tetracycline efflux protein was found to be located on plasmid pBC46-TL of B. cereus BA117. In vitro conjugative transfer indicated that pBC46-TL can be transferred into Bacillus invictae BA142, Bacillus safensis BA143, and Bacillus licheniformis BA130. The frequencies were of 1.5 × 10^?7 to 1.7 × 10^?5 transconjugants per donor cells. Therefore, Bacillus strains with acquired antibiotic resistance may represent a potential risk for the spread of antibiotic resistance between Bacillus and other clinical pathogens via horizontal gene transfer.     

冷藏鲤鱼和罗非鱼优势腐败菌腐败能力分析

通过分析接种腐败菌的鲤鱼和罗非鱼无菌鱼块贮藏中感官、腐败代谢产物和腐败菌的变化,以腐败菌的生长动力学参数和腐败代谢产物的产量因子(YTVBN/CFU)为指标,探讨冷藏鲤鱼和罗非鱼优势腐败菌假单胞菌和腐败希瓦氏菌的腐败能力。结果表明:接种腐败希瓦氏菌和恶臭假单胞菌的鲤鱼无菌鱼块的货架期分别为132h和162h,此时的TVBN值为27.12mg/100g和22.51mg/100g,腐败希瓦氏菌和恶臭假单胞菌菌数为8.96 lg(CFU/g)和9.07 lg(CFU/g),产量因子YTVBN/CFU为9.28×10-9mg TVBN/CFU和1.81×10-8mg TVBN/CFU。接种荧光假单胞菌和腐败希瓦氏菌的罗非鱼无菌鱼块的货架期分别为132h和144h,此时的TVBN值为23.46mg/100g和24.30mg/100g,荧光假单胞菌和腐败希瓦氏菌菌数为8.83 lg(CFU/g)和9.12 lg(CFU/g),产量因子YTVBN/CFU为1.67×10-8mg TVBN/CFU和9.10×10-9mg TVBN/CFU。结合两种养殖鱼冷藏过程中的菌相变化和腐败菌在腐败过程中的作用,初步得出冷藏罗非鱼和鲤鱼的特定腐败菌是假单胞菌,两种腐败菌都具有较强的腐败能力。     

Short communication: In vitro antimicrobial susceptibility of Prototheca wickerhamii and Prototheca zopfii isolated from bovine mastitis

Bovine mastitis caused by Prototheca spp. can assume high significance because of economic losses and the potential risk to public health. Studies on the susceptibility of Prototheca spp. to antimicrobials have demonstrated its high level of resistance. We report the susceptibility of bovine isolates of Prototheca wickerhamii and Prototheca zopfii to amphotericin B and nystatin, 2 antifungal agents commonly used in the control of protothecosis, and discuss the results. After subculture, minimum inhibitory concentrations of both antifungal drugs were determined using macrodilution and agar diffusion methods. The inoculum concentration was standardized by determination of colony-forming units per milliliter. Nystatin showed more efficacy than amphotericin B in inhibiting P. wickerhamii growth. In contrast, growth inhibition of P. zopfii was similar for both antifungal agents. This study demonstrates different in vitro susceptibility patterns of P. wickerhamii and P. zopfii, reinforcing the necessity for more investigation into drugs that can be used with clinical efficacy.     

Cellular injuries of spray-dried Lactobacillus spp. isolated from kefir and their impact on probiotic properties

The injuries caused by spray drying (SD) of three potential probiotic lactobacilli isolated from kefir grains and the impact on some probiotic properties, were evaluated. Results demonstrated that Lactobacillus plantarum 83114 and L. kefir 8321 showed a slight reduction of viability (0.11 and 0.29 log CFU/ml respectively) after SD process, and L. kefir 8348 was found to be more sensitive to the process with a reduction in viability of 0.70 log CFU/ml. Neither membrane damage, evaluated by increased sensitivity to NaCl, lysozyme, bile salt and penicillin G, nor changes in acidifying activity in MRS and milk by lactobacilli were detected after SD. L. plantarum 83114 and L. kefir 8321 after SD did not lose their capacity to adhere to intestinal cells. Nevertheless, L. kefir 8348 showed a significant loss of adhesion capacity after SD. In addition, rehydrated spray-dried L. kefir 8321 retained the ability to protect against Salmonella invasion of intestinal cells. This effect was observed when L. kefir is co-incubated with Salmonella before invasion assay.This work shows that the membrane integrity evaluated by indirect methods and some probiotic properties of lactobacilli isolated from kefir did not change significantly after SD, and these powders could be used in functional foods applications.     

Molecular characterization and antibiotic resistance of Staphylococcus spp. isolated from cheese processing plants

The aim of this research paper was to characterize coagulase-positive and coagulase-negative staphylococci from raw milk, Minas cheese, and production lines of Minas cheese processing. One hundred isolates from 3 different cheese producers were characterized using molecular approaches, such as PCR, molecular typing, and DNA sequencing. Staphylococcus aureus (88% of the isolates) was the most abundant followed by Staphylococcus epidermidis, Staphylococcus hyicus, and Staphylococcus warneri. Among the 22 enterotoxin genes tested, the most frequent was seh (62% of the isolates), followed by selx and ser. Hemolysin genes were widely distributed across isolates, and Panton-Valentine leukocidin and toxic shock syndrome toxin genes were also identified. Methicillin-resistant S. aureus were staphylococcal cassette chromosome mec III, IVa, IVd, and others nontypeable. In the phenotypic antibiotic resistance, multiresistant isolates were detected and resistance to penicillin was the most observed. Using spa typing, we identified several types and described a new one, t14969, isolated from cheese. These findings suggest that antibiotic resistance and potentially virulent strains from different sources can be found in the Brazilian dairy processing environment. Further research should be conducted with collaboration from regulatory agencies to develop programs of prevention of virulent and resistant strain dissemination in dairy products and the processing environment.     

风味咸鱼中乳酸菌和葡萄球菌的分离与鉴定

为优化咸鱼的加工工艺,对优质北海淡口咸鱼进行乳酸菌和葡萄球菌的分离和鉴定。分别采用MRS和MSA培养基,从咸鱼中分离出乳酸菌13 株和葡萄球菌10 株。经生理生化实验初筛出乳酸菌3 株、葡萄球菌两株。初步鉴定乳酸菌为戊糖片球菌,两株葡萄球菌分别为肉糖葡萄球菌和木糖葡萄球菌。     

Development of multiplex loop-mediated isothermal amplification-RFLP (mLAMP-RFLP) to detect Salmonella spp. and Shigella spp. in milk

A multiplex loop-mediated isothermal amplification-RFLP (mLAMP-RFLP) was developed and validated for simultaneous detection of Salmonella strains and Shigella strains in milk. In this system, two sets of LAMP primers were designed to specifically target invA of Salmonella spp. and ipaH of Shigella spp. Under isothermal conditions at 63 °C, ladder pattern of DNA bands could be amplified within 60 min in the presence of genomic DNAs of Salmonella strains and Shigella strains, which could be distinguished between Salmonella spp. and Shigella spp. simultaneously based on the different ladder pattern of DNA bands and subsequent restriction enzyme analysis. The overall analysis time was approximately 20 h including the enrichment of the bacterial cells, which greatly saved detection time. The sensitivity of mLAMP was found to be 100 fg DNA/tube with genomic DNAs of Salmonella strains and Shigella strains, comparatively, multiplex PCR was 1 pg DNA/tube. The mLAMP allowed the detection of milk sample artificially contaminated by Salmonella strains and Shigella strains at initial inoculation levels of approximate 5 CFU/10 mL. In conclusion, the mLAMP described here can potentially facilitate simultaneous monitoring of Salmonella and Shigella in a large number of food samples, which could be used as a primary screening method and as a supplement to classical detection method.     

Short communication: Diversity of species and transmission of antimicrobial resistance among Staphylococcus spp. isolated from goat milk

The increasing production of goat milk and its derivatives is affected by the occurrence of intramammary infections, which are highly associated with the presence of Staphylococcus species, including some with zoonotic potential. Staphylococci in general can exchange mobile genetic elements, a process that may be facilitated by the isolate's capacity of forming biofilms. In this study we identified, to the species level, Staphylococcus isolated from goat milk samples by MALDI-TOF and confirmed the identification by sequencing housekeeping genes (rrs and tuf). Eight species were identified, more than half being either Staphylococcus epidermidis or Staphylococcus lugdunensis. The isolates were shown by pulsed-field gel electrophoresis to be genetically diverse between the studied herds. Resistance to ampicillin and penicillin was widespread, and 2 Staph. epidermidis isolates contained the methicillin-resistance gene mecA. Most of the isolates that were resistant to at least 1 of the 13 antimicrobials tested harbored plasmids, one of which was demonstrated to be conjugative, being transferred from a Staph. epidermidis to a Staphylococcus aureus strain. Biofilm formation was observed in almost every isolate, which may contribute to their capacity of exchanging antimicrobial resistance genes in addition to acting as a physical barrier to the access of drugs. Our results showed that antimicrobial resistance among goat staphylococci may be emerging in a process facilitated by the exchange of mobile genetic elements between the bacteria and the establishment of biofilms, which calls for careful monitoring and more effective control therapies.     

草鱼腐败菌Pseudomonas putida和Shewanella putrefaciens互作对其致腐能力的影响

草鱼贮藏期间易由于微生物的生长繁殖发生腐败变质,一定程度上制约了其加工产业的发展。微生物互作是影响食品腐败的重要因素,为探究微生物互作在草鱼品质劣变中的作用,将Pseudomonas putida(P. putida)和Shewanella putrefaciens(S. putrefaciens)混合接种至草鱼鱼肉和精氨酸溶液中,通过测定鱼肉贮藏期间菌落总数、可溶性肽、游离氨和腐胺等指标的变化,以及精氨酸溶液中的腐胺产量,揭示草鱼腐败微生物P. putida和S. putrefaciens互作效应对这2种菌生长和致腐能力的影响。结果表明,P. putida具有较强的产嗜铁素能力,并通过竞争三价铁离子抑制了鱼肉中S. putrefaciens的生长。P. putida和S. putrefaciens互作升高了贮藏前11d鱼肉中游离氨和贮藏前8d鱼肉中腐胺的含量,但对鱼肉中可溶性肽的生成没有促进作用。贮藏11d后,由于S. putrefaciens的生长受到抑制,P. putida和S. putrefaciens没有通过互作效应促进游离氨和腐胺的产生。P. putida可以通过精氨酸脱亚胺酶途径为S. putrefaciens提供精氨酸降解产物,从而增强S. putrefaciens产腐胺的能力。整体来说,P. putida和S. putrefaciens在贮藏期(0～11d)内会通过代谢共栖等菌间互作效应增强致腐能力,并加速草鱼理化指标劣变。S. putrefaciens在草鱼腐败及2种微生物间的互作效应中起基础作用,今后在鱼肉贮藏保鲜技术开发中应注重对S. putrefaciens的控制研究。     

Comparison of antimicrobial resistance in Salmonella and Campylobacter isolated from turkeys in the Midwest USA

The current study was carried out to determine the antimicrobial resistance profiles and evaluate some molecular characteristics of a set of Salmonella and Campylobacter isolates recovered from production line turkeys in the Midwest region of the United States. A total of 94 birds identified as being positive for both Salmonella and Campylobacter spp. were selected for study. All Salmonella isolates were examined for antimicrobial resistance using the methods employed in the National Antimicrobial Resistance Monitoring System (NARMS). Campylobacter isolates were subjected to similar analysis using the Etest^®. In addition, polymerase chain reaction (PCR) was carried out to determine the presence of the antimicrobial resistance associated genes, integrase (int1), class 1 integrons (Salmonella and Campylobacter) and a multidrug efflux pump (Campylobacter spp.). Results from the study showed that the Salmonella and Campylobacter isolates examined displayed resistance to a number of antimicrobials, with Salmonella and Campylobacter isolates being resistant to at least three antimicrobials while some isolates showed resistances to 6 or 8 different antimicrobials. In addition, 68.1% of the Salmonella isolates tested were found to be positive for the class I integrase gene (int1), 28.7% possessed a 1000 bp gene cassette and 17% possessed an 800 bp gene cassette. All Campylobacter isolates were negative for int1, but 36.2% tested positive for the Campylobacter multidrug efflux pump (CmeB). A considerable number of Salmonella and Campylobacter isolates tested displayed varying degrees of antimicrobial resistance as well as the presence of some factors associated with the carriage and persistence of antimicrobial resistance. Similarities in the types of antimicrobial resistance observed in Campylobacter and Salmonella strains was evident. The results of this study suggest that prescribing practice at the farm level may be a factor in promoting antimicrobial resistance in more than one species of organism. Such practices may, therefore, contribute to the potential health risk for consumers should micro-organisms carrying multiple antimicrobial resistances enter the food chain. This study may be one of the first to report on the incidence of the multidrug efflux pump (CmeB) in Campylobacters recovered from processed turkeys. The antimicrobial resistance and molecular characteristics of Salmonella and Campylobacter is discussed.     

Evolution under different storage conditions of anomalous blue coloration of Mozzarella cheese intentionally contaminated with a pigment-producing strain of Pseudomonas fluorescens

Several widespread occurrences of anomalous blue coloration of Mozzarella cheese have been recorded in the United States and some European countries. Official laboratory analysis and health authorities have linked the occurrences to contamination of the processing water with strains of Pseudomonas fluorescens, although several experts questioned how to unequivocally link the blue color to the presence of the microorganism. To establish a method to determine whether a given Pseudomonas spp. strain is responsible for the defect and study the evolution of the coloration under different storage conditions, we developed an in vitro system for the evaluation of blue coloration of Mozzarella cheese intentionally contaminated with strains of P. fluorescens. The purpose of the system was to determine whether P.fluorescens strains, isolated from Mozzarella cheese with anomalous blue coloration, were able to reproduce the blue coloration under controlled experimental conditions. Thirty-six trials of experimental inoculation of Mozzarella cheese in different preservation liquids were conducted using various suspensions of P.fluorescens (P. fluorescens ATCC 13525, P.fluorescens CFBP 3150, and P. fluorescens 349 field strain isolated from blue-colored Mozzarella cheese) at different concentrations and incubated at different temperatures. Growth curves of all tested P.fluorescens strains demonstrated that after 3 d of incubation the concentration was generally >10⁶ cfu/g of Mozzarella cheese incubated in either tryptic soy broth (control) or conditioning brine. Prolonged incubation for 5 d at either 20°C or 8°C led to concentrations up to 10⁹ cfu/g of Mozzarella cheese incubated in tryptic soy broth and up to 10⁸ cfu/g of Mozzarella cheese incubated in preservation liquid. All Mozzarella cheeses inoculated with the field strain of P. fluorescens, except those opened 1 h after packaging and stored at 8°C, showed the characteristic anomalous blue coloration, which appeared from 1 to 72 h after opening the packaging, and was proportional to colony count, duration of storage, and storage temperature. With the proposed system, which enabled a larger number of samples to be analyzed under controlled experimental conditions and a large amount of data to be generated in a short time, we described precisely how and under which conditions the presence of P. fluorescens in Mozzarella cheese is responsible for the anomalous blue coloration. The system will help producers intercept contaminated batches and help consumers avoid the conditions under which the defect can appear.     

进口印茄木与甘巴豆显微构造比较

对我国进口的印茄木与甘巴豆木材从三个切面的微观构造特征上进行对比分析,找出它们的异同点,从而准确地鉴别。     

Characterization of new sources of mungbean (Vigna radiata (L.) Wilczek) resistance to bruchids, Callosobruchus spp. (Coleoptera: Bruchidae)

The bruchid beetles Callosobruchus chinensis (L.) and C. maculatus (F.) are destructive pests of stored mungbean (Vigna radiata (L.) Wilczek). The development of resistant mungbean varieties to manage bruchids is a major breeding objective. In the present study, we investigated the characteristics of resistance to C. chinensis and C. maculatus in two new resistant mungbean accessions V1128 and V2817, and two previously reported resistant accessions V2709 and V2802, compared to the susceptible mungbean cultivar, KPS1. Evaluation for resistance to both bruchid species using whole and decorticated seeds revealed that V1128 and V2817 were free from damage, V2709 and V2802 showed partial damage with low or moderate number of bruchids emerging from seeds, and KPS1 showed complete damage with the highest number of bruchids emerged. Comparison of the seeds harvested at seed filling, early maturity and full maturity stages revealed that the percentage of damaged seeds from resistant accessions was lower at all stages compared with KPS1. V1128 and V2817 showed complete resistance against both bruchids regardless of when their seeds were harvested, while resistance in V2709 and V2802 were most pronounced at full maturity, and KPS1 was totally damaged at all times tested. These results suggest that the chemical factor(s) conferring resistance is synthesized as early as the seed filling stage. Evaluation of resistance using artificial seeds showed that increasing the percentage of resistant seed powder adversely affected bruchid growth and development. The number of adults emerging from seeds and number of damaged seeds decreased while adult developmental period increased as the proportion of resistant seed powder increased. The weight of emerging male and female adults of C. maculatus was lighter than those from the seeds containing susceptible seed powder alone. However, C. chinensis adults were not affected by the same test. The results suggest that biochemical(s) in cotyledon tissue are responsible for the resistance and the seed coat had no protective role against the bruchids. Although all four resistant accessions evaluated are useful for mungbean breeding, V1128 and V2817 show complete resistance to both C. chinensis and C. maculatus. Thus, these two new resistant sources may be the most effective for breeding purposes.