Transmembrane diffusion of hydrophobic antimicrobial agents and cell surface hydrophobicity in Bacteroides fragilis

The transmembrane diffusion of hydrophobic antimicrobial agents, e.g. lincomycin and clindamycin, was examined in Bacteroides fragilis which is sensitive to these agents. The results showed that these agents penetrate efficiently through the outer membrane. Cell surface hydrophobicity measured by the partition assay between water and p-xylene revealed that the cell surface of B. fragilis is more hydrophobic than that of Salmonella typhimurium or Pseudomonas aeruginosa. Furthermore, treatment with low concentrations of surfactant caused cell lysis. These results suggest that the cell surface hydrophobicity in B. fragilis plays an important role in the efficient transmembrane penetration of hydrophobic compounds. This efficiency explains the susceptibility of B. fragilis to hydrophobic antimicrobial agents.     

Cytosolic Ca2+-Concentrations and Distributions in Rhizoids of Chara fragilis Desv. Determined by Ratio Analysis of the Fluorescent Probe Indo-1

Rhizoids of Charafragilis Desv. were iontophoretically loaded with the Ca²⁺-sensitive ratio dye indo-1. After loading, the rhizoids regained their preinjection-membrane potential within 2 to 5 min and survived the procedure for more than 24 h, but their growth in length was permanently inhibited. Microfluorimetric measurements of the indo-1 fluorescence-ratio showed spontaneous fluctuations of the cytoplasmic Ca²⁺-concentration, usually declining from high values after loading to 425 ± 80 nM (± SD, n = 7) as determined by in-vitro calibration. Increasing the extracellular K⁺-concentration (0.1 mM to 10 mM) or Ca²⁺-concentration (1 mM to 10 mM) led to increases of 100 to 200 nM in cytoplasmic Ca²⁺-concentration. The spatial distribution of cytosolic Ca²⁺ in the rhizoid tips was visualised in ratio images computed from low-light video-pictures. These images showed a fairly homogeneous distribution of Ca²⁺ throughout the tip cytoplasm with concentrations being in the same range as determined by microfluorimetry. A tip-to-base gradient in cytoplasmic Ca²⁺, thought to be a prerequisite for cell polarity and tip growth, was found in only 1 out of 16 successfully microinjected cells. Additionally, a progressive compartmentalization of the fluorochrome indo-1, probably in the proplastids and the very abundant endoplasmic reticulum of the rhizoids, was observed.     

A unified stoichiometric model for oxidative and oxidoreductive growth of yeasts

Yeasts degrade glucose through different metabolic pathways, where the choice of the pathway is dependent on the nature of the limitation in the various substrates. When oxygen is limiting in addition to glucose, yeasts often grow according to a mixture of oxidative and reductive metabolism. Oxygen may be limiting either by supply or by inherent biological restrictions such as the respiratory bottleneck in Saccharomyces cerevisiae or by both. A unified model incorporating both supply and biological limitations is proposed for the quantitative prediction of growth rates, consumption and production rates, as well as key metabolite concentrations during mixed oxidoreductive metabolism occuring as a result of such oxygen limitations. This simple unstructured model can be applied to different yeast strains while at the same time requiring a minimum number of measured parameters. "Estimators" are utilized in order to predict the presence of supply-side or biological limitations. The values of these estimators also characterize the relative importance of oxidative to total metabolism. Results from the aerobic and oxygen-limited chemostat cultures were used to corroborate the model predictions. During these experiments, the heat released by the yeast cultures was also monitored on-line. The model correctly predicted the overall stoichiometry, steady-state concentrations, and rates including heat dissipation rates measured in the various situations of oxygen limitations. Direct continuous measurements such as heat can be used in conjunction with the unified model for on-line proces control. (c) 1992 John Wiley & Sons, Inc.     

脆弱拟杆菌BF839治疗寻常型银屑病：一项单臂、开放初步临床试验

银屑病被认为是一种T细胞主导的炎症性疾病,其发病与肠道菌群失调密切相关。脆弱拟杆菌 (Bacteroides fragilis,BF) 可通过调节T细胞的细胞因子表达起抗炎作用。目前尚无脆弱拟杆菌用于治疗银屑病的相关报道,文中率先探究脆弱拟杆菌BF839对银屑病的治疗效果。选择2019年4月至2019年10月广州医科大学附属第二医院就诊的27例银屑病患者,维持原治疗不变,口服脆弱拟杆菌BF839 12周,对比治疗前后银屑病皮损面积与严重程度指数 (Psoriasis area and severity index,PASI) 评分,统计治疗12周后药物减停率。结果表明,12周试验完成率为96.3% (26/27),12周PASI30 (PASIN定义为治疗后PASI评分下降≥N%的患者比例) 为65.4%,PASI50为42.3%,PASI75为19.2%;治疗前PASI评分为9.1±5.9,治疗12周后PASI评分为5.8±4.9,具有显著统计学差异 (P<0.01);治疗12周后皮肤瘙痒程度用视觉模拟量表 (Visual analog scale,VAS) 评分有效率为42.3%,治疗前VAS评分为2.9±2.2,治疗12周后VAS评分为2.3±2.1,无显著统计学差异 (P>0.05)。患者治疗12周内不良反应率为3.8% (1/26),其中便秘1例,药物减停率为60.0%。以上结果提示脆弱拟杆菌BF839可能对银屑病治疗有一定疗效,可降低PASI评分及药物使用率,不良反应少,值得进一步研究。     

Primordial germ cells: what does it take to be alive?

Specification of primordial germ cells (PGCs) in the proximal epiblast enables about 45 founder PGCs clustered at the base of the allantoic bud to enter the embryo by active cell movement. Specification of the PGC lineage depends on paracrine signals derived from the somatic cell neighbors in the extraembryonic ectoderm. Secretory bone morphogenetic proteins (BMP) 4, BMP8b, and BMP2 and components of the Smad signaling pathway participate in the specification of PGCs. Cells in the extraembryonic ectoderm induce expression of the gene fragilis in the epiblast in the presence of BMP4, targeting competence of PGCs. The fragilis gene encodes a family of transmembrane proteins presumably involved in homotypic cell adhesion. As PGCs migrate throughout the hindgut, they express nanos3 protein. In the absence of nanos3 gene expression, no germ cells are detected in ovary and testis. During migration and upon arrival at the genital ridges, the population of PGCs is regulated by a balanced proliferation/programmed cell death or apoptosis. Paracrine and autocrine mechanisms, involving transforming growth factor-beta1 and fibroblast growth factors exert stimulatory or inhibitory effects on PGCs proliferation, modulated in part by the membrane-bound form of stem cell factor. Apoptosis requires the participation of the pro-apoptotic family member Bax, whose activity is balanced by the anti-apoptotic family member Bcl21/Bcl-x. In addition, a loss of cell-cell contacts in vitro results in the apoptotic elimination of PGCs. It needs to be determined whether apoptosis is triggered by a failure of PGC to establish and maintain appropriate cell-cell contacts with somatic cells or whether undefined survival factors released by adjacent somatic cells cannot reach physiological levels to satisfy needs of the expanding population of PGCs.     

Occurrence of enterotoxigenic and nonenterotoxigenic Bacteroides fragilis in calves and evaluation of their antimicrobial susceptibility

Bacteroides fragilis is considered an important clinical pathogen and the most common anaerobe isolated from human and animal clinical specimens; enterotoxigenic strains produce diarrhea. The presence of enterotoxigenic (ETBF) and nonenterotoxigenic B. fragilis in stool samples from calves with or without acute diarrhea and the antimicrobial susceptibility of the strains were evaluated. The stool samples were plated onto a selective B. fragilis-bile-esculin agar, and incubated anaerobically (10% CO(2)/90% N(2)), at 37 degrees C, for 72 h. Species of the B. fragilis group were identified by using the API 32-A kit. Enterotoxigenic strains were detected by PCR and the cytotoxic assay. From 54 diarrhea and 54 nondiarrhea stools, 124 and 92 members of the B. fragilis group, respectively, were recovered. Only two ETBF strains were isolated from two different diarrhea samples and the bft gene was detected in both. Moreover, the bft gene was detected in DNA from four different diarrheal stools samples but no ETBF strain was recovered. All the bacteria were susceptible to chloramphenicol, imipenem, moxifloxacin, piperacillin/tazobactam, metronidazole and tigecycline. Most of the isolates from both calves with and without diarrhea were resistant to all metals. Our results are of concern, and suggest the need to increase the surveillance of antibiotic and metal resistance of this microbial group isolated from animal production such as calves.     

Pyrosequencing of prey DNA in reptile faeces: analysis of earthworm consumption by slow worms

Little quantitative ecological information exists on the diets of most invertebrate feeding reptiles, particularly nocturnal or elusive species that are difficult to observe. In the UK and elsewhere, reptiles are legally required to be relocated before land development can proceed, but without knowledge of their dietary requirements, the suitability of receptor sites cannot be known. Here, we tested the ability of non-invasive DNA-based molecular diagnostics (454 pyrosequencing) to analyse reptile diets, with the specific aims of determining which earthworm species are exploited by slow worms (the legless lizard Anguis fragilis) and whether they feed on the deeper-living earthworm species that only come to the surface at night. Slow worm faecal samples from four different habitats were analysed using earthworm-specific PCR primers. We found that 86% of slow worms (N=80) had eaten earthworms. In lowland heath and marshy/acid grassland, Lumbricus rubellus, a surface-dwelling epigeic species, dominated slow worm diet. In two other habitats, riverside pasture and calciferous coarse grassland, diet was dominated by deeper-living anecic and endogeic species. We conclude that all species of earthworm are exploited by these reptiles and lack of specialization allows slow worms to thrive in a wide variety of habitats. Pyrosequencing of prey DNA in faeces showed promise as a practical, rapid and relatively inexpensive means of obtaining detailed and valuable ecological information on the diets of reptiles.     

Cytokine release and expression induced by OmpA proteins from the Gram-negative anaerobes, Porphyromonas asaccharolytica and Bacteroides fragilis

OmpA proteins from Gram-negative anaerobes Porphyromonas asaccharolytica and Bacteroides fragilis induced release and expression of IL-1alpha, tumor necrosis factor (TNF)-alpha, IFN-gamma, IL-6, and IL-10 from murine splenocytes in vitro in a dose-dependent fashion. The release of the cytokines induced by B. fragilis Bf-OmpA was at much lower levels compared with P. asaccharolytica Omp-PA; Bf-OmpA did not induce release of IL-10. Omp-PA and Bf-OmpA were able to upregulate mRNA expression of the tested cytokines. The results obtained with refolded Bf-OmpA were similar to those with native Bf-OmpA. The data presented in this research demonstrate for the first time that Omps from anaerobic bacteria can induce the release of cytokines, suggesting that Omp-PA and Bf-OmpA may play important roles in the pathogenic processes of these bacteria.     

天然砂与修饰砂对病毒的吸附与去除

分别在不同pH、含有不同金属阳离子及腐殖酸的脱氯自来水与蒸馏水中,研究了砂与金属氢氧化物修饰砂吸附与去除Polivirus 1(PV1)和Bacteroides fragilis phage(B．fp)的不同效果。结果显示,天然砂吸附病毒效率随水体pH的降低而增加,但当砂表面经氧氧化铝、氢氧化铁沉积修饰后,却在中性pH具有较高的吸附率。金属阳离子可促进天然砂吸附病毒,并随其浓度和价态的增加而增加,但对修饰砂作用不明显。腐殖酸对砂及修饰砂吸附病毒的影响也不同,修饰砂吸附病毒不受腐殖酸的存在及其浓度影响,而天然砂会因腐殖酸的存在及其浓度的提高而降低吸附病毒效率。在任一实验条件下,砂与修饰砂在自来水中的吸附病毒效率高于在蒸馏水中的吸附效率,扫描电镜观察显示砂与修饰砂具有明显不同的表面结构特征,这是两者具有不同吸附效率的基础。从砂与修饰砂吸附PV1的效率高于B．fp的现象说明B．fp是一个更为合适的病毒去除指示生物。本实验结果表明了金属氢氧化物修饰砂可为传统的净水工艺提供高效的病毒去除过滤介质与途径。     

Swimming behavior and morphometry of the file shell Limaria fragilis

Swimming has evolved in only a few orders of Bivalves. In this study, the behavior, morphometry, and mechanics of swimming in the file shell Limaria fragilis were characterized and compared to the better understood scallops. Absolute swimming speed (cm sec^-1) increased with increasing shell height, although relative swimming speed (body lengths sec^-1) did not covary with shell height. The increase in absolute swimming speed was due to an increase in the distance covered during each valve clap as clap distance (cm clap^-1) also increased with shell height while clapping frequency (claps sec^-1) did not covary with animal size. Limaria fragilis displayed a variety of morphological changes related to size. Shell length was negatively allometric with shell height indicating the shell became proportionately slimmer in larger animals. Dry shell mass was negatively allometric with shell height, while both dry adductor muscle mass and dry mantle + tentacle mass were positively allometric. Autotomy of mantle tentacles significantly decreased clap distance by 13% without affecting clapping frequency or swimming speed.