Discrimination of Staphylococcus aureus biotypes by pulsed-field gel electrophoresis of DNA macro-restriction fragments

AIMS: To examine whether pulsed-field gel electrophoresis (PFGE) of DNA macro-restriction fragments could provide better discrimination among the different biotypes previously described within the species Staphylococcus aureus than the traditional biochemical approach. METHODS AND RESULTS: Seventy three Staph. aureus strains from various sources (human, animal or food origin) and belonging to eight biotypes, including the poultry-like biotype, tentatively designated as an 'abattoir' biotype, were genotyped by PFGE after SmaI digestion of DNA. The PFGE patterns were compared using the average linkage matching method (UPGMA) with the Dice coefficient. A total of 61 PFGE patterns were observed, showing between 31 and 100% similarity. In most cases, strains with the same biotype were grouped specifically into one, two or three separate sub-clusters. Strains from the 'abattoir' biotype were clustered in one separate sub-cluster. CONCLUSIONS: The PFGE typing is useful to distinguish the traditional biotypes of Staph. aureus and has a more discriminatory power than the biochemical typing. SIGNIFICANCE AND IMPACT OF THE STUDY: The PFGE typing confirms the 'abattoir' biotype as a separate group on a genetic level and is well suited to investigate modes of staphylococcal contamination of food.     

A novel DNA microarray design for accurate and straightforward identification of Escherichia coli safety and laboratory strains

Escherichia coli K-12, B, C and W strains and their derivates are declared in biological safety guidelines as risk group 1 organisms as they are unable to colonise the human gut.

Differentiation and identification of these safety strains is mainly based on pulsed-field gel electrophoresis (PFGE), phage sensitivity tests or PCR-based methods. However, these methods are either tedious and time consuming (phage sensitivity, PFGE) or based on single specific fragments (PCR) or patterns (PFGE) lacking additional information for further differentiation of the strains.

In the current study, subtractive hybridisation techniques were applied to detect specific DNA fragments which were used to design a microarray (chip) for accurate and simple identification of these organisms, and to differentiate them from other E. coli strains. The chip can be used to identify E. coli safety strains and monitor them during ongoing experiments for changes in their genome and culture purity. The hybridisation layout of the microarray was arranged in such a way that the respective lineages of safety strains could be easily identified as distinct letters (K, B, C or W). Differentiation of single strains or subtyping was possible with further probes. In addition, a set of probes targeting genes coding for common virulence factors has been included, both to differentiate safety strains from pathogenic variants and to make sure that no transfer of these genes happens during handling or storage. The reliability of the approach has been tested on a comprehensive selection of E. coli laboratory strains and pathogenic representatives.     

Virulence properties of rough and smooth strains of Vibrio cholerae O1

A comparative study was carried out to see the differences in pathogenicity of rough and smooth strains. A total of 10 strains including 5 each of rough and smooth strains of Vibrio cholerae O1 were tested and found positive for toxin production by enzyme-linked immunosorbent assay (ELISA) in Richardson's and AKI media. All the smooth and rough strains, except one, showed a titre of 1: 10 and 1: 100 in Richardson's and AKI media, respectively. Both types of strains produced enterotoxin in rabbit ileal loop (RIL). The differences in multiplication abilities of smooth and rough strains in RIL were statistically significant (P <0.05). However, these differences in multiplying abilities did not influence the adherence potential or enterotoxin production as there was no significant difference (P >0.05) between these properties. This study demonstrated that the rough strains are equally pathogenic and as important as smooth strains.     

Field efficacy of a mixture of atoxigenic Aspergillus flavus Link:Fr vegetative compatibility groups in preventing aflatoxin contamination in maize (Zea mays L.)

Competitive exclusion of aflatoxin producers by endemic atoxigenic strains of Aspergillus flavus is a proven tool for aflatoxin management being adapted for use in Africa. Field efficacy of an experimental formulation consisting of four native atoxigenic strains (La3303, La3304, La3279 and Ka16127) was evaluated on maize in 2007 and 2008 in four agroecological zones in Nigeria. The four atoxigenic strains were individually formulated on sterile sorghum grain and subsequently mixed in equal proportions. The blended product was applied on soil (40 kg/ha), 2–3 weeks before flowering. Grains from treated and untreated fields were analyzed for aflatoxins at harvest and after storage. Proportions of the A. flavus population composed of each of the four applied strains in soil before treatment and in harvested grains were determined using vegetative compatibility analyses. Application of the strain mixture resulted in reduced aflatoxin content and significantly (P < 0.05) increased the combined frequencies of the vegetative compatibility groups (VCGs) of the applied strains recovered from the soil and grain. Aflatoxin reductions of 67–95% were associated with a 74–80% combined incidence of the VCGs of the four atoxigenic strains on the treated crops. The applied atoxigenic strains remained with the crop into storage and reduced postharvest increases in contamination. The results suggest that the evaluated multi-strain formulated product has potential to contribute to reduced aflatoxin contamination in Nigeria. This is the first report of a field evaluation of an endemic strain mixture effective at reducing aflatoxin contamination during crop development.     

Replication of small effect quantitative trait loci for behavioral traits facilitated by estimation of effect size from independent cohorts

Quantitative trait locus (QTL) mapping is often done in a single segregating population, such as a backcross or an intercross. Both QTL location and effect size are then estimated from the same dataset. This approach results in an over-estimate of effect size for two reasons: (1) LOD scores, which are maximized over numerous point-wise tests, are correlated with estimated effect size and (2) small effect QTLs are often undetected in underpowered experiments, yielding inflated effect sizes for detected QTLs (the Beavis effect). When it is impractical to maintain or generate large population sizes, an alternative is to use two populations, one for initial detection and localization and a second for a locus-matched estimate of effect size, not conditioned on significance. Recombinant inbred (RI) panels are eminently suitable for this approach, as each strain genotype can be sampled repeatedly. We present mapping results from the LXS RI panel for two behavioral phenotypes relating to ethanol response: low-dose ethanol activation and loss of righting following high-dose injection. Both the phenotypes were measured in two or three independent cohorts, which were then used to re-estimate effect size. Many small-effect QTLs replicated using this approach, but in all cases, effect size, in the replicate cohorts, was reduced from the initial estimate, often substantially. Such a reduction will have important consequences for power analyses in which sample sizes are determined for subsequent confirmation studies.     

强力霉素抗性基因目标供体菌、受体菌和接合子的筛选及鉴定

目的为进一步研究环境中病原微生物目标供体菌强力霉素抗性基因(Dox)水平传播机制奠定基础。方法以强力霉素抗性基因为筛选指标,通过药敏试验从7个菌株中筛选出遗传型分别为Dox~RX~S的候选供体菌和Dox~SX~R的候选受体菌(X代表不是强力霉素的抗生素),将供、受体菌共培养后筛选出遗传型为Dox~RX~R的接合子。分别测定X对目标供体菌、Dox对目标受体菌的最小抑菌浓度。对目标供、受体菌从形态学、生理生化、分子生物学和BIOLOG方面进行鉴定。结果研究的7个病原菌均为多重耐药,最多能耐受15种抗生素,对链霉素、萘啶酮酸和磺胺二甲嘧啶的耐药率最高(100%),对庆大霉素、诺氟沙星和环丙沙星的耐药率最低(0%)。目标供体菌、受体菌和接合子Con-Ⅱ基因型分别为Dox~RKan~S、Dox~SKan~R和Dox~RKan~R。Kan对目标供体菌的最小抑菌浓度为0.310 0μg/mL,Dox对目标受体菌的最小抑菌浓度为0.048 8μg/mL。目标供体菌(Dox~RKan~S)鉴定为Escherichia coli O157:H7(E.coli O157:H7),目标受体菌TR-M30-1(Dox~SKan~R)鉴定为产酸克雷伯菌。结论目标供体菌为E.coli O157:H7(Dox~RKan~S),目标受体菌为TR-M30-1(Dox~SKan~R),接合子为Con-Ⅱ(Dox~RKan~R)。     

微生物法合成红景天苷

红景天苷是红景天属植物的主要有效成分之一,具有耐缺氧、抗辐射、抗疲劳、抗肿瘤、降血糖、提高免疫力等多重功效。随着其需求量的日益增加和植物资源的不断减少,微生物法合成红景天苷因具有周期短和易调控等优势而倍受关注。目前微生物法合成红景天苷尚处于基础研发阶段,为了方便相关领域研究者系统了解其研究现状和探讨其未来发展方向,文中对红景天苷生物合成途径、糖基转移酶、野生菌/天然酶资源和工程菌/重组酶体系进行了综述。     

产酯酶微生物菌种的筛选研究

研究了产酯酶微生物的筛选,包括筛选模型、酶活力检测方法及菌株的分布。对30多份土样以及实验室保存的菌种进行了大量的筛选,以添加三醋酸甘油酯、乳酸乙酯酯类物质对土样等样品富集,采用添加显色剂溴甲酚紫的快速简便平板显色法,观察水解变色圈直径和菌落直径的大小进行初筛。获得两者直径之比相对大的菌株174株,采用平板打孔检测法和摇瓶发酵比色法测酶活力相结合进行复筛,最终得到酯酶活力较高的24株菌株。就初筛和复筛方法及结果加以比较分析,复筛菌株做不同底物的酶活力检测,建立了一个有效、简便及快速的微生物酯酶的筛选模型。并对酯酶产生菌的立体选择专一性进行了初步考察。     

番茄青枯雷尔氏菌强致病力菌株变异的研究

为研究番茄青枯雷尔氏菌强致病力菌株的变异,探索了继代培养、在NB培养基上不同时间培养、不同pH处理7d和15d、不同温度处理1h后对强致病力菌株变异的影响。结果表明:随着继代培养的培养代数增加,平均弱化指数成增大趋势,在第10代出现了无致病力菌株;在NB培养基上培养15d时,强致病力菌株已完全转化为不确定菌株和无致病力菌株,在培养30d时,强致病力菌株几乎完全转化为无致病菌株;pH7.0时,处理7d和15d后,强致病力菌株比例均为最大,分别为93.33%和92.22%,pH5.8时,强致病力菌株比例最低,分别为46.67%和31.11%;用不同温度处理强致病力菌株发现,温度50℃时,菌株死亡,温度40℃时,活菌数显著低于其他(4~30℃)处理,强致病力菌株比例为4~40℃所有处理中最低。     

浓香型白酒糟醅及窖泥产香功能菌的研究进展

浓香型白酒主要香气物为己酸乙酯、乳酸乙酯、乙酸乙酯和丁酸乙酯四大酯类,白酒微生物发酵过程中酯类合成主要是酸与醇在酯化酶的作用下产生,因此产香功能菌包括香气及其前体物产生菌和酯化酶产生菌.本文综述了浓香型白酒糟醅及窖泥主要产香功能菌的来源、组成、鉴定方法、功能特性、相互关系及其在浓香型白酒生产过程中的应用等方面的研究进展,旨为浓香型白酒重要微生物的研究提供思路,为其发酵过程控制提供理论依据.     

Binding of mouse fibrinogen to Candidaalbicans in vivo

Binding of fibrinogen to various Candida albicans strains has been investigated by immunofluorescence microscopy on kidney sections of experimentally infected mice. Fibrinogen appeared to bind to both mycelium and blastospores in situ whereas previous studies, carried out in vitro, have shown fibrinogen binding to mycelial elements only.     

Starch Gel Electrophoresis: An Effective Method for Separation of Pathogenic and Nonpathogenic Naegleria Strains*

SYNOPSIS. Isoenzyme electrophoresis of 7 different enzyme systems was used to compare 24 strains of Naegleria fowleri and 6 strains of N. gruberi. The 30 strains could be grouped into 4 distinct categories based upon zymogram patterns. No interstrain band variation in all enzyme systems was demonstrated in pathogenic strains of N. fowleri. Three nonpathogenic high temperature-tolerant strains of Naegleria had similar zymograms. Four of the 5 remaining nonpathogenic Naegleria strains had no interstrain band variation. Based upon zymograms, the 22 pathogenic strains constitute a homogenous species. Similarly the high temperature-tolerant nonpathogenic strains formed a cohesive group. The remaining nonpathogenic strains could be separated into 2 groups.     

侵染香蕉的黄瓜花叶病毒株系的血清学特征

香蕉花叶病三类不同症状,即断续条纹类（BS）、连续条纹类（CS）和斑驳类（MM）在田间广泛存在,经过血清学、生物学、核酸斑点杂交和反转录聚合酶链反应,已确定它们都由黄瓜花叶病毒（Cucumberm。。i。virus,CMV）所弓愧f’］。这三类症状分离物在鉴别寄主、粒子形态、粒子电泳相对迁移率以及在西葫芦（CI;curbitafor）和烟草（Nicotianatabacumcv．HV38）上增殖和运转动力学的特征也表现不同［’］。这些不同可能揭示了香蕉三类分离物分属不同的株系。血清学是鉴定和研究CMV株系间亲缘关系的重要依据。大量文献【’,‘1报道…     

Plasmid content in Yersinia pestis strains of different origin

Plasmid content in 242 Yersinia pestis strains from various natural plague foci of the U.S.S.R. and other countries was studied. Of these strains, 172 (71%) were shown to carry three plasmids described previously of about 6, 45-50 and 60 MDa, respectively. Twenty strains (8%) from different foci harboured additional cryptic plasmids, most often of about 20 mDa in size. Plasmid pPst displayed considerable constancy of its molecular mass. On the contrary, size variations of pCad (45-49 MDa) and, especially, pFra (60-190 MDa) were found. Molecular mass of these plasmids correlated with the host strain origin.     

木糖发酵重组菌研究进展

木糖发酵是植物纤维原料生物转化制取乙醇商业化生产的基础和关键 ,但自然界存在的微生物菌株不能满足商业化生产的需要。利用基因工程技术对细菌和酵母进行改造 ,以提高它们在厌氧条件下的木糖发酵能力成为目前研究和开发的重点。通过转基因和基因删除技术 ,主要对Escherichiacoli、Zymomonasmobilis、Pichiastipitis和Saccharomycescerevisiae等典型的乙醇发酵菌株实施基因改造 ,构建出一系列不同类型的木糖发酵重组菌株。与野生型菌株相比 ,重组菌株在厌氧条件下的木糖发酵能力得到了不同程度的改善 ,但是它们仍然未能投入于商业化生产。微生物的木糖代谢工程和木糖发酵重组菌株的构建有待于进一步的深入研究 。     

赤霉素产生菌的激光,化学复合诱变育种研究

采用激光和氯化锂复合诱变赤霉菌,对其产生的赤霉素中活性最高的ＧＡ３含量作为效价测定。结果表明与出发菌株相比,激光诱变,ＬｉＣｌ诱变,复合诱变效价分别提高为１１３．７％,４０．２％,１８９．６％。展示激光复合诱变是遗传育种的一种有效方法。     

果胶酶产生菌的分离及培养条件研究

从黑龙江省巴彦县亚麻厂不同发酵时期的沤麻液中 ,分离得到两株果胶酶产生菌MHZP 0 1和MHZP 0 2 ,经初步鉴定为芽孢杆菌属 (Bacillus)。在温度为 33～ 37℃ ,pH 5～ 6,工业级原料C N(质量比 )为 1∶1时 ,为这两株菌的最佳培养条件。