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PubMed1991

[Contacts between the cells in bacterial colonies].

The interaction of cells in microbial colonies has been studied by electron-microscopic techniques. Two types of contacts between cells have been found to exist in the colonies of Gram-negative bacteria of the genera Escherichia, Shigella and Salmonella: close cell adhesion due to the fusion of cell-wall outer membranes and the formation of intersections consisting of membranous tubules. At the sites of close adhesion the fusion of cytoplasmic and outer membranes have been found to occur in Bayer's zones. In the colonies of Gram-positive bacteria of the genera Staphylococcus and Brevibacterium only one type of contacts has been revealed: the fusion of the peptidoglycan layers of the cell walls. The results of this study indicate that in colonies bacteria are not completely isolated; their interaction leads to the formation of a three-dimensional structure denoted as a cooperative cell system.

Bacteria↗
PubMed2026

Ecological Filtering by Tuber Compartments Shapes Stable Core Microbiomes That Underpin Potato Plant Growth Across Environments.

Harnessing plant microbiomes for sustainable agriculture requires understanding not only whether they can boost crop performance, but also how ecological processes govern their assembly, stability, and functional contributions across environments. While we previously showed that seed tuber microbiomes can predict potato vigour using machine learning, it remained unclear how ecological processes shape tuber microbiome stability and functionality across host genotypes, tuber compartments, soil types, and years. Here, we analyzed the national-scale dataset of 240 field-collected potato seedlots, spanning six genotypes, two soil types, and two growing years, with a focus on the spatially distinct heel and eye compartments of the potato tuber. By profiling over 1200 bacterial and fungal communities and linking microbiome composition to plant performance, we show that plant genotype and tuber compartment are the strongest determinants of microbial diversity and composition. Compartment-specific enrichment of functional traits revealed spatial partitioning of microbial functions, with organic compound conversion and nitrogen cycling dominant in the heel, and energy metabolism enriched in the eye. Applying a macroecological abundance-occupancy framework, we identified a stable core microbiome of bacterial and fungal taxa that persisted across all environments and years. These core members were more strongly associated with plant growth-related traits than non-core taxa, and core taxa in different tuber compartments showed distinct correlations with taxa of potential pathogenic relevance. Together, our findings demonstrate that tuber compartments act as ecological filters that structure persistent, functionally specialised microbiomes linked to plant growth-related traits across environments. By providing an ecological and functional framework for compartment-resolved, stable core microbiomes, this study advances mechanistic understanding of plant-microbe interactions and identifies stable microbial partners as promising targets for improving potato resilience and productivity.

Journal Article↗
PubMed2000

Molecular techniques for determining microbial diversity and community structure in natural environments.

The ability to quantify the number and kinds of microorganisms within a community is fundamental to the understanding of the structure and function of an ecosystem. The simple morphology of most microbes provides few clues for their identification and physiological traits are often ambiguous. In addition, many organisms resist cultivation, which is essential to their characterization. Recombinant DNA techniques have provided a means whereby many of the obstacles associated with cultivation and description can be overcome and subsequently has allowed many new insights into the complexity of natural microbial communities. Molecular approaches based on 16S ribosomal RNA (rRNA) sequence analysis allow direct investigation of the community structure, diversity, and phylogeny of microorganisms in almost any environment, while quantification of the individual types of microorganisms or entire microbial communities may be addressed by nucleic acid hybridization techniques. Furthermore, the use of fluorescently labeled population-specific rRNA probes allows microscopic examination of individual cells in complex microbial assemblages as well as their interactions in situ. In this review, we discuss strategies for characterizing microbial communities without the need for cultivation.

DNA, Ribosomal↗
PubMed1995

Lectins--proteins with a sweet tooth: functions in cell recognition.

Lectins, non-enzymic proteins that bind mono- and oligosaccharides reversibly and with high specificity, occur widely in nature. They come in a variety of sizes and shapes, but can be grouped in families with similar structural features. The combining sites of lectins are also diverse, although they are similar in the same family. The specificities of lectins are determined by the exact shape of the binding sites and the nature of the amino acid residues to which the carbohydrate is linked. Small changes in the structure of the sites, such as the substitution of only one or two amino acids, may result in marked changes in specificity. The carbohydrate is linked to the protein mainly through hydrogen bonds, with added contributions from van der Waals contacts and hydrophobic interactions. Coordination with metal ions may occasionally play a role too. Microbial surface lectins serve as a means of adhesion to host cells of viruses (e.g. influenza virus), bacteria (e.g. E. coli) and protozoa (e.g. amoeba): a prerequisite for the initiation of infection. Blocking the adhesion by carbohydrates that mimic those to which the lectins bind prevents infection by these organisms. The way is thus open for the development of anti-adhesive therapy against microbial diseases. Lectin-carbohydrate mediated interactions between leucocytes and endothelial cells are the first step in the recirculation of lymphocytes and in the migration of neutrophils to sites of inflammation. Such interactions may also feature highly in the formation of metastases. Studies of these processes are expected to lead to the development of carbohydrate-based anti-adhesion drugs for the treatment of inflammatory diseases as well as cancer.

Animals↗
PubMed1988

Does iron inhibit cryptoendolithic microbial communities?

Photosynthetic activity of three cryptoendolithic microbial communities was studied under controlled conditions in the laboratory. In two of these communities, the dominant organisms were lichens, collected from Linnaeus Terrace and from Battleship Promontory. The third community, dominated by cyanobacteria, was collected from Battleship Promontory. Both sites are in the ice-free valleys of southern Victoria Land. Previous efforts have shown how physical conditions can influence metabolic activity in endolithic communities (Kappen and Friedmann 1983; Kappen, Friedmann, and Garty 1981; Vestal, Federle, and Friedmann 1984). Biological activity can also be strongly influenced by the chemical environment. Inorganic nutrients such as nitrate, ammonia, and phosphate are often limiting factors, so their effects on photosynthetic carbon-14 bicarbonate incorporation were investigated. Iron and manganese are two metals present in Linnaeus Terrace and Battleship Promontory sandstones, and their effects on photosynthesis were also studied. The results may add to our understanding of biogeochemical interactions within this unique microbial community.

Ammonia↗
PubMed2003

Interactions between M proteins of Streptococcus pyogenes and glycosaminoglycans promote bacterial adhesion to host cells.

Several microbial pathogens have been reported to interact with glycosaminoglycans (GAGs) on cell surfaces and in the extracellular matrix. Here we demonstrate that M protein, a major surface-expressed virulence factor of the human bacterial pathogen, Streptococcus pyogenes, mediates binding to various forms of GAGs. Hence, S. pyogenes strains expressing a large number of different types of M proteins bound to dermatan sulfate (DS), highly sulfated fractions of heparan sulfate (HS) and heparin, whereas strains deficient in M protein surface expression failed to interact with these GAGs. Soluble M protein bound DS directly and could also inhibit the interaction between DS and S. pyogenes. Experiments with M protein fragments and with streptococci expressing deletion constructs of M protein, showed that determinants located in the NH2-terminal part as well as in the C-repeat region of the streptococcal proteins are required for full binding to GAGs. Treatment with ABC-chondroitinase and HS lyase that specifically remove DS and HS chains from cell surfaces, resulted in significantly reduced adhesion of S. pyogenes bacteria to human epithelial cells and skin fibroblasts. Together with the finding that exogenous DS and HS could inhibit streptococcal adhesion, these data suggest that GAGs function as receptors in M protein-mediated adhesion of S. pyogenes.

Bacterial Adhesion↗
PubMed2006

The anti-microbial peptide LL-37 inhibits the activation of dendritic cells by TLR ligands.

The endogenous anti-microbial peptide LL-37/hCAP-18 is an effector molecule of the innate host defense system at surfaces of the body. Besides its direct anti-microbial activity, the peptide interacts with different cell types. Dendritic cells (DCs) play a central role in mucosal host defense. It was the aim of the study to determine whether LL-37 modulates the response of DCs to pathogen-associated molecular patterns. Monocyte-derived DCs were stimulated with the Toll-like receptors (TLRs) ligands LPS, lipoteichoic acid and flagellin. We measured classical markers of DC maturation and assayed the ability of the DCs to activate T cell responses. Co-incubation with LL-37 resulted in suppressed activation of DCs. Levels of released IL-6, IL-12p70 and TNF-alpha and surface expression of HLA-DR, CD80, CD83, CD86 and the chemokine receptor CCR7 were decreased. Exposure of DCs to LL-37 during LPS exposure induced co-cultured naive T cells to produce less IL-2 and IFN-gamma and decreased their proliferation. The response of memory T cells to a recall antigen was also decreased. In conclusion, we demonstrate that the anti-microbial peptide LL-37 inhibits the activation of DCs by TLR ligands. We propose that LL-37 is a regulator of host defense responses at the intersection of innate and adaptive immune systems.

Amino Acid Sequence↗
PubMed2000

Quantifying the hurdle concept by modelling the bacterial growth/no growth interface.

The hurdle concept described eloquently over many years by Professor Leistner and his colleagues draws attention to the interaction of factors that affect microbial behaviour in foods. Under some circumstances these effects are additive. Under others the implication is that synergistic interactions lead to a combined effect of greater magnitude than the sum of constraints applied individually. Predictive modelling studies on the combined effects of temperature and water activity and temperature and pH suggest that the effect of these combinations on growth rate is independent. Where the effect of the two factors is interactive rather than independent is at the point where growth ceases--the growth/no growth interface. An interesting and consistent observation is that a very sharp cut off occurs between conditions permitting growth and those preventing growth, allowing those combinations of factors to be defined precisely and modelled. Growth/no growth interface models quantify the effects of various hurdles on the probability of growth and define combinations at which the growth rate is zero or the lag time infinite. Increasing the stringency of one or more hurdles at the interface by only a small amount will significantly decrease the probability of an organism growing. Understanding physiological processes occurring near the growth/no growth interface and changes induced by moving from one side of the interface to the other may well provide insights that can be exploited in a new generation of food preservation techniques with minimal impact on product quality.

Bacteria↗
PubMed2006

Modification of adherence to plastic and to human buccal cells of Candida albicans and Candida dubliniensis by a subinhibitory concentration of itraconazole.

Exposure to subinhibitory concentrations of antifungal agents can influence the adherence of Candida spp. to the host cell. In this study the adherence of Candida albicans ATCC 10231 and Candida dubliniensis CECT 11455 to plastic and to human buccal epithelial cells was evaluated following pre-exposure to 0.5 x minimum inhibitory capacity (MIC) of itraconazole and compared with the corresponding cellular surface hydrophobicity. The yeasts were grown in Sabouraud broth or RPMI-1640 with itraconazole (0.5 x MIC) for 24-26 h at 37 degrees C and the drug was then removed. The adhesion capacity to plastic was studied by turbidimetry in a polystyrene microtiter plate. The adhesion of the yeast to buccal epithelial cells was determined using microscopy techniques. The cellular surface hydrophobicity levels were determined by the microbial adhesion hydrocarbons test. Pre-exposure to itraconazole decreased plastic adherence and cellular surface hydrophobicity in both species when grown in RPMI. When C. albicans was grown in Sabouraud broth, it was nonhydrophobic and did not adhere and therefore no change was detected with the antibiotic. Itraconazole increased adherence to buccal epithelial cells in both species and media studied, as compared to controls without antifungal agents. To study the effects of these antifungal agents on pathogenicity mechanisms, it will be necessary to standardize the methodology for evaluation to determine their in vivo therapeutic efficacy.

Adhesiveness↗
PubMed1999

Chromium-resistant soil actinomycetes: their tolerance to other metals and antibiotics.

Chromium occurs widely in most soils, but generally in trace amounts. Actinomycetes, one of the important components of the microbial population in soils interact with a variety of metals including chromium. This study was aimed to evaluate the tolerance of soil actinomycetes to Cr6+, other metals and antibiotics. Thirty-two actinomycete isolates were screened for their tolerance to Cr6+ on tryptone yeast extract agar medium supplemented with Cr6+ at concentrations ranging from 100 to 2000 micrograms ml-1. Thirteen Cr-tolerant isolates were selected on the basis of their growth at the highest concentration, but their performance was not satisfactory in Cr6+ containing liquid salts medium. Resistance of these isolates to other metals and antibiotics was assessed using agar-cup assay and disc diffusion technique, respectively. The sequence of metal toxicity for the actinomycete isolates was in the order Hg2+ > Ni2+ > Cu2+ > Co2+ > Cd2+, but the Cr6+ resistance of the isolates could not be correlated with their antibiotic-resistance profile.

Actinomycetales↗
PubMed2025

Impact of RNA extraction on respiratory microbiome analysis using third-generation sequencing.

BACKGROUND: The respiratory microbiome, which comprises bacteria, fungi, and viruses, plays a crucial role in respiratory health and disease. However, its study is limited by the low microbial biomass in respiratory samples and the dominance of host RNA. Metatranscriptomics offers comprehensive insights into active microbial communities and their interactions with the host but requires optimized RNA extraction protocols for robust and unbiased analysis. This study evaluated two RNA extraction kits&#x2014;one employing chemical lysis (CL) and another combining chemical and mechanical lysis (CML)&#x2014;to determine their effectiveness for metatranscriptomic analysis of respiratory samples. RESULTS: The CML protocol significantly increased double-stranded DNA (dsDNA) library yields, leading to higher sequencing read counts for both sample types (p&#x2009;<&#x2009;0.0001). The read length was unaffected by the lysis protocol for the BAL and NPS samples. Taxonomic profiling revealed that CML enhanced the detection of robust microorganisms, such as gram-positive bacteria and fungi, without compromising viral detection. CONCLUSIONS: The CML protocol demonstrated superior recovery of genetic material, particularly for fungi and gram-positive bacteria, making it better suited for comprehensive metatranscriptomic analyses. These findings underscore the need for tailored RNA extraction strategies on the basis of sample type and research objectives. Optimized metatranscriptomic protocols are pivotal for advancing our understanding of the respiratory microbiome and its role in health and disease.

Microbiota↗
PubMed2003

Dendritic cells and host resistance to infection.

Host defence against infection requires an integrated response of both the innate and adaptive arms of the immune system. Emerging data indicate that dendritic cells contribute an essential part to the initiation and regulation of adaptive immunity. Dendritic cells guard the sites of pathogen entry to the host and are uniquely suited to detect and capture invading microbes. Upon recognition of microbial structures and appropriate activation, a maturation programme is triggered and dendritic cells migrate to lymphoid organs to stimulate a primary cell-mediated immune response. Moreover, dendritic cells play a critical role in shaping the emerging response, thereby controlling the course of infection. They can discriminate between various types of microorganisms and are capable of producing different cytokines in response to different microbial stimuli. On the other hand, pathogens developed numerous strategies to evade and subvert dendritic cell functions. Elucidating the interactions of dendritic cells with microbial pathogens may lead to novel strategies for combating infectious diseases by dendritic cell-based vaccination and immunotherapy. This review highlights recent advances in our knowledge of the unique role of dendritic cells in counteracting microbial infections.

Animals↗
PubMed2026

Isolation of folate-producing probiotic candidates and their effects on homocysteine metabolism and gut microbiota composition.

BACKGROUND: Folate deficiency is a global nutritional problem associated with multiple adverse health outcomes, including impaired one-carbon metabolism and elevated homocysteine levels (hyperhomocysteinemia). Gut microbiota-mediated folate biosynthesis has emerged as a promising strategy for improving the host's folate status. This study aimed to isolate folate-producing probiotic strains, clarify their folate synthesis mechanisms, and evaluate their regulatory effects on folate metabolism and gut microbiota. METHODS: High-throughput cultivation and screening were performed to isolate folate-producing candidate probiotics. Whole-genome sequencing analysis, pathway reconstruction, and metabolite profiling in fermented milk were performed to explore folate biosynthesis pathways and microbial cross-feeding interactions. A folate-deficient mouse model was established to evaluate the effects of a candidate probiotic cocktail on serum folate, homocysteine (Hcy) levels, and gut microbiota composition using quantitative PCR (qPCR) and 16S rRNA gene sequencing. RESULTS: High-throughput screening identified 8 high-folate-producing candidate probiotic strains, including Lactiplantibacillus plantarum and Heyndrickxia coagulans, from over 1,000 isolates. Genomic analysis revealed that most commonly used probiotics lacked para-aminobenzoic acid (pABA) biosynthesis genes but retained downstream modules, suggesting a reliance on cross-feeding with pABA-producing gut commensals such as Bacteroides. Metabolite profiling of fermented milk demonstrated that selected strains significantly increased bioactive 5-methyltetrahydrofolate (5-MeTHF) and tetrahydrofolate levels. In vivo, only a high-dose candidate probiotic cocktail significantly elevated serum folate (p&#x202f;<&#x202f;0.05) and reduced homocysteine levels (p&#x202f;<&#x202f;0.05) in deficient mice. Fecal qPCR confirmed dose-dependent transient persistence of the administered bacterial species. Consistent with the qPCR data, 16S rRNA gene sequences demonstrated significant enrichment of these administered species observed in the high-dose group. Furthermore, beta-diversity analysis found that high-dose candidate probiotic supplementation promoted a shift in the gut microbiota composition toward a normal profile, partially mitigating the dysbiosis induced by the folate-deficient diet. This effect was accompanied by a significant enrichment of potential short-chain fatty acid producers (e.g., Lachnospiraceae and Oscillospiraceae) and the depletion of potential opportunistic pathogens. CONCLUSION: This study screened high-folate-producing candidate probiotic strains and demonstrated their ability to synthesize the active form of 5-MeTHF. Moreover, folate-producing candidate probiotic cocktail treatment significantly improved folate status and Hcy metabolism and modulated the gut microbiota by enriching potential beneficial bacterial taxa. These findings suggested that folate-producing probiotics may serve as a promising microbiota-based strategy to improve folate availability and homocysteine metabolism.

B vitamin↗
PubMed2006

Molecular mechanisms of bacterial resistance to antimicrobial peptides.

Cationic antimicrobial peptides (CAMPs) are integral compounds of the antimicrobial arsenals in virtually all kinds of organisms, with important roles in microbial ecology and higher organisms' host defense. Many bacteria have developed countermeasures to limit the efficacy of CAMPs such as defensins, cathelicidins, kinocidins, or bacteriocins. The best-studied bacterial CAMP resistance mechanisms involve electrostatic repulsion of CAMPs by modification of cell envelope molecules, proteolytic cleavage of CAMPs, production of CAMP-trapping proteins, or extrusion of CAMPs by energy-dependent efflux pumps. The repertoire of CAMPs produced by a given host organism and the efficiency of microbial CAMP resistance mechanisms appear to be crucial in host-pathogen interactions, governing the composition of commensal microbial communities and the virulence of bacterial pathogens. However, all CAMP resistance mechanisms have limitations and bacteria have never succeeded in becoming fully insensitive to a broad range of CAMPs. CAMPs or conserved CAMP resistance factors are discussed as new mediators and targets, respectively, of novel and sustainable anti-infective strategies.

Animals↗
PubMedDate not supplied

Gram-negative bacillary colonization and bacteremia in the compromised host.

A complex interaction of host and microbial factors is unquestionably related to the pathogenesis of gram-negative rod bacteremia in neutropenic, immunocompromised patients. In this paper we summarize evidence that colonization of the gastrointestinal tract often precedes systemic invasion by klebsiellae and Pseudomonas aeruginosa, but that the factors directly responsible for the weakening of barriers to colonization remain poorly understood. Additionally, bacteremic isolates of Escherichia coli appear to segregate into commonly occurring groups by O and K antigens. A broadened investigation of E. coli surface (fimbrial) antigens indicates several common hemagglutination patterns of bloodstream isolates with various mammalian erythrocytes, but these patterns may also be strongly associated with commonly encountered O and K types. This epidemiologic and microbiologic information may be useful both in clinical management and in following measures to prevent infection in high risk immunocompromised patients.

Adhesiveness↗
PubMed1987

In vitro activity of ampicillin plus sulbactam against anaerobes compared to ampicillin and cefoxitin.

The antimicrobial susceptibility of 195 recent clinical isolates of anaerobic bacteria was studied to ampicillin alone, ampicillin + 1 mg/l sulbactam, ampicillin + 5 mg/l sulbactam, and cefoxitin by means of agar dilution tests. The ampicillin-sulbactam combinations were the most effective drugs against species of the Bacteroides fragilis group, the MIC90 of ampicillin + 5 mg/l sulbactam for B. fragilis being less than 1 mg/l, compared to 256 mg/l of ampicillin, 4 mg/l of ampicillin + 1 mg/l sulbactam, and 8 mg/l of cefoxitin. No significant difference between ampicillin alone and in combination with sulbactam was observed against gram-positive anaerobic rods, Peptococcus spp. and Peptostreptococcus spp. with MIC's less than 2 mg/l.

Ampicillin↗
PubMed1995

Criteria for testing the susceptibility of Streptococcus pneumoniae to cefotaxime and its desacetyl metabolite using 1 microgram or 30 micrograms cefotaxime disks.

In vitro susceptibility tests were performed with 350 selected strains of Streptococcus pneumoniae to evaluate disk diffusion tests with 30 micrograms and 1 microgram cefotaxime disks. Zones were compared to MICs of cefotaxime with and without its desacetyl metabolite. Cefotaxime was two to eight times more active than desacetyl cefotaxime, but the two compounds were additive when combined in vitro. For 30 micrograms disks, zone size breakpoints were < or = 27 mm, 28-30 mm and > or = 31 mm for resistant, intermediate and susceptible, respectively. For 1 microgram disks, those zone size criteria were reduced to < or = 13 mm, 14-16 mm and > or = 17 mm. The 30 micrograms disk that is currently available for testing other species can be used for testing pneumococci; however, the 1 microgram disk has some important advantages.

Cefotaxime↗