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At least 1,621 records · Page 90Linked to original sources
PubMed1996

How many ruminal bacteria are there?

With the development of strictly anaerobic techniques and habitat-simulating media, a variety of bacteria were isolated from the rumen in the 1940s and 1950s. Based on standard morphological and physiological characteristics, the microbial ecosystem of the rumen contains a very complex population of bacteria. In recent years, ruminal bacteria have been re-evaluated with newer, more objective, and genetically valid methods of classification. Ribosomes are complicated structures, and their DNA-encoding sequences are relatively free from selective pressure. Because ribosomes have evolved slowly, they provide a long-term natural history of evolution. The invariable and hypervariable regions of rRNA genes can be used to group bacteria into kingdoms, genera, and species. The 16S rRNA sequences have provided a basis for renaming some ruminal species (Bacteroides amylophilus is now Ruminobacter amylophilus and Bacteroides succinogenes is now Fibrobacter succinogenes) and for classifying at least one recently isolated ruminal bacterium (e.g., Clostridium aminophilum). The DNA:DNA hybridization is a more sensitive method of assessing bacterial relatedness than is 16S rRNA. Bacterial strains within a species should have a high degree of DNA:DNA homology, but some species of ruminal bacteria (e.g., Prevotella ruminicola and Butyrivibrio fibrisolvens) had highly unrelated strains. Studies of 16S rRNA and DNA:DNA hybridization indicate that the diversity of ruminal bacteria has been greatly underestimated. Traditional studies of phylogeny of ruminal bacteria were stymied by the fastidious growth requirements of many ruminal bacteria, and enumeration was tedious and inaccurate. Modern methods of bacterial classification do not require in vitro culture and have the potential of detecting even a single cell.

Animal Nutritional Physiological Phenomena↗
PubMed1990

[Approximation of the dynamics of microbial contamination of the Segre River in Lérida].

The water rivers contains a basal autochthonus population of micro-organisms which is local and temporal and it is modified by the incoming sewage. In this paper a simple model is applied to estimate the faecal bacterial load poured from the town of Lérida to the Segre River and the downstream assimilation capacity of this river. In spite of the inherent limitations and imprecision due to sampling operations and calculations, the numerical results are related to other published results. The evolution of faecal bacterial population downstream of Lérida does not follow the theoretical model without a growth coefficient. The showed data on faecal pollution (bacteriological and viral detectors) are the only ones which have been published on the final section, the most disturbed, of the Segre River.

Bacteria↗
PubMed1991

A model for diurnal patterns of carbon fixation in a Precambrian microbial mat based on a modern analog.

Microbial mat communities are one of the first and most prevalent biological communities known from the Precambrian fossil record. These fossil mat communities are found as laminated sedimentary rock structures called stromatolites. Using a modern microbial mat as an analog for Precambrian stromatolites, a study of carbon fixation during a diurnal cycle under ambient conditions was undertaken. The rate of carbon fixation depends primarily on the availability of light (consistent with photosynthetic carbon fixation) and inorganic carbon, and not nitrogen or phosphorus. Atmospheric PCO2 is thought to have decreased from 10 bars at 4 Ga (10(9) years before present) to approximately 10(-4) bars today, implying a change in the availability of inorganic carbon for carbon fixation. Experimental manipulation of levels of inorganic carbon to levels that may have been available to Precambrian mat communities resulted in increased levels of carbon fixation during daylight hours. Combining these data with models of daylength during the Precambrian, models are derived for diurnal patterns of photosynthetic carbon fixation in a Precambrian microbial mat community. The models suggest that, even in the face of shorter daylengths during the Precambrian, total daily carbon fixation has been declining over geological time, with most of the decrease having occurred during the Precambrian.

Bacteria↗
PubMed1997

Staphylococcal necrotizing fasciitis in the mammary region in childhood: a report of five cases.

OBJECTIVE: Necrotizing fasciitis is a highly lethal soft tissue infection rarely reported in childhood. The initiating site is usually a local trauma or a surgical wound. We observed five cases of necrotizing fasciitis the initiating site for which was the mammary region and discuss their management. STUDY DESIGN: We describe these five patients and review the clinical characteristics of their presentation. RESULTS: Staphylococcal necrotizing fasciitis was observed in the mammary region in all five cases. Four children were newborn infants with a mammitis preceding the onset of necrotizing fasciitis. Surgical débridement was done only after the fourth day from onset of illness. All children were discharged in good condition after 1 month. Two have been followed until puberty, with destruction of the mammary gland in one case and good development in the other one. CONCLUSION: Mammitis may be the initiating event for necrotizing fasciitis in neonates. Necrotizing fasciitis is a life-threatening disease; patients require early intensive care, parenteral antibiotic therapy, and surgical débridement. In a few instances surgery can be carefully delayed until the necrotic area is more delineated if the condition is diagnosed early during disease evolution and appropriate treatment is instituted in intensive care units.

Anti-Bacterial Agents↗
PubMed2001

Antibiotic resistance with particular reference to soil microorganisms.

Evidence of increasing resistance to antibiotics in soil and other natural isolates highlights the importance of horizontal transfer of resistance genes in facilitating gene flux in bacteria. Horizontal gene transfer in bacteria is favored by the presence of mobile genetic elements and by the organization of bacterial genomes into operons allowing for the cooperative transfer of genes with related functions. The selective pressure for the spread of resistance genes correlates strongly with the clinical and agricultural overuse of antibiotics. The future of antimicrobial chemotherapy may lie in developing new antimicrobials using information from comparative functional microbial genomics to find genetic targets for antimicrobials and also to understand gene expression enabling selective targeting of genes with expression that correlates with the infectious process.

Anti-Bacterial Agents↗
PubMed2001

Drosophila scavenger receptor CI is a pattern recognition receptor for bacteria.

One hallmark of innate immunity apparently conserved from primitive life forms through to humans is the ability of the host to recognize pathogen-associated molecular patterns (PAMPs). Since macrophage pattern recognition receptors are not well defined in Drosophila, we set out to identify such receptors. Our findings reveal that Drosophila macrophages express multiple pattern recognition receptors and that the Drosophila scavenger receptor, dSR-CI, is one such receptor capable of recognizing both gram-negative and gram-positive bacteria, but not yeast. Our data indicate that scavenger receptor bacterial recognition is conserved from insects to humans and may represent one of the most primitive forms of microbial recognition.

Amino Acid Sequence↗
PubMed1999

Antibiotic use in humans and bacterial resistance.

As with any public health problem, the evolution of antibacterial resistance must be viewed from a perspective of risk, and analysed in terms of probabilities within the populations. It is necessary to be able to predict the risk of antibacterial resistance, in the future, and two main strategies have recently been developed in mathematical models that may help to evaluate these risks. It is also important to understand how antibiotics are used and how their use affects the evolution of antibacterial resistance. Understanding the epidemiology of antibacterial resistance will enable us to develop preventive strategies to limit existing resistance and to avoid the emergence of new strains of resistant bacteria.

Anti-Bacterial Agents↗
PubMed1999

The effect of nutrients on feed intake in ruminants.

The purpose of the present review is to examine the role played by nutrients in controlling feed intake in ruminants, in light of their particular anatomical, physiological, nutritional and behavioural characteristics. The ration is first digested in the rumen for several hours by microbial fermentation. Volatile fatty acids, which constitute 50-75% of a ruminant's energy supply, considerably depress feed intake when administered by short-term infusion into the rumen. However, this effect seems to be largely due to osmolarity problems. Only propionate seems to have a specific action, unrelated to osmolarity, in the mesenteric or portal veins. Nitrogenous nutrients have little short-term effect on feed intake, except when there is excess NH3 in the rumen. Metabolic cues from intestinal digestion, particularly of glucose and starch, have very little short- or long-term influence in controlling feed intake, in comparison with rumen digestion cues. However, the short-term responses in feeding behaviour do not always reflect longer-term effects on feed intake control. The effects of volatile fatty acid infusion on feed intake are much less significant over the long term, except in the case of propionate. The nutrients required for good microbial activity (proteins in the rumen) generally promote feed intake, whereas nutrients that disrupt rumen functioning (lipids) reduce feed intake. After a learning period, preferences are always governed by a tendency toward optimum rumen functioning, rather than by animal nutritional requirements, although the two factors are not independent. Ruminants, due to their particular anatomical and nutritional characteristics, have, in the course of their evolution, developed specific feed intake control mechanisms based on nutritional cues.

Animal Nutritional Physiological Phenomena↗
PubMed2002

A brief overview of modern directions in marine DOC studies part II--recent progress in marine DOC studies.

Progress made in analytical techniques allows the formulation of new concepts in the biogeochemistry of organic carbon. The second part of our review summarizes the latest evolution and introduces new ideas in the biogeochemistry of marine dissolved organic carbon (DOC). Via classification of different fractions and sources of DOC, characterization of its composition, age and availability for bacterial utilization, and fate of DOC, we show the role of DOC in the global carbon cycle and the significance of bulk DOC in the oceans. Special emphasis is placed on the microbial loop in the cycling of DOC and its relation with higher trophic levels (phytoplankton and zooplankton). Significant progress has also been made in the study of the roles of colloidal organic material in metal complexation, ultraviolet radiation in dissolved organic matter photochemical oxidation, and chromophore-containing constituents of DOC as the signature of DOC for satellite observations. The importance of bulk DOC in the global carbon cycle requires the inclusion of this fraction in the regional and global carbon models. We predict that future DOC study in the ocean will focus on the development of sophisticated, almost continuously recording, moored DOC instrument arrays for the monitoring of small-scale DOC horizontal and vertical patchiness; widespread time series stations including estuarine, coastal and open environments; more detailed chemical characterization of different fractions of organic carbon from diverse marine habitats; parameterization of predictive models of DOC cycling on regional and global scales, incorporating the microbial loop; and finally, monitoring of DOC dynamics from satellites on regional and global scales.

Carbon↗
PubMed2003

A complex microbiota from snowball Earth times: microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA.

A thin carbonate unit associated with a Sturtian-age ( approximately 750-700 million years ago) glaciogenic diamictite of the Neoproterozoic Kingston Peak Formation, eastern California, contains microfossil evidence of a once-thriving prokaryotic and eukaryotic microbial community (preserved in chert and carbonate). Stratiform stromatolites, oncoids, and rare columnar stromatolites also occur. The microbial fossils, which include putative autotrophic and heterotrophic eukaryotes, are similar to those found in chert in the underlying preglacial units. They indicate that microbial life adapted to shallow-water carbonate environments did not suffer the significant extinction postulated for this phase of low-latitude glaciation and that trophic complexity survived through snowball Earth times.

Biological Evolution↗
PubMed2002

Genome fragment of Wolbachia endosymbiont transferred to X chromosome of host insect.

The adzuki bean beetle, Callosobruchus chinensis, is triple-infected with distinct lineages of Wolbachia endosymbiont, wBruCon, wBruOri, and wBruAus, which were identified by their wsp (Wolbachia surface protein) gene sequences. Whereas wBruCon and wBruOri caused cytoplasmic incompatibility of the host insect, wBruAus did not. Although wBruCon and wBruOri were easily eliminated by antibiotic treatments, wBruAus persisted over five treated generations and could not be eliminated. The inheritance pattern of wBruAus was, surprisingly, explained by sex-linked inheritance in male-heterozygotic organisms, which agreed with the karyotype of C. chinensis (2n = 20, XY). Quantitative PCR analysis demonstrated that females contain around twice as much wsp titer as males, which is concordant with an X chromosome linkage. Specific PCR and Southern blot analyses indicated that the wBruAus-bearing strain of C. chinensis contains only a fraction of the Wolbachia gene repertoire. Several genome fragments of wBruAus were isolated using an inverse PCR technique. The fragments exhibited a bacterial genome structure containing a number of ORFs typical of the alpha-proteobacteria, although some of the ORFs contained disruptive mutations. In the flanking region of ftsZ gene, a non-long terminal repeat (non-LTR) retrotransposon sequence, which is typical of insects but not found from bacteria, was present. These results strongly suggest that wBruAus has no microbial entity but is a genome fragment of Wolbachia endosymbiont transferred to the X chromosome of the host insect.

Animals↗
PubMed2002

The effects of volatile microbial secondary metabolites on protein synthesis in Serpula lacrymans.

The effects of volatile secondary metabolites produced by Trichoderma pseudokoningii, Trichoderma viride and Trichoderma aureoviride on growth rate and protein synthesis in two Serpula lacrymans isolates were investigated. Mycelial growth was affected to differing degrees, depending on the specific interactive microbial couplet involved. Protein synthesis by both S. lacrymans (Forfar) and S. lacrymans (H28) was affected by the volatile secondary metabolites of T. aureoviride and T. viride, but not by those of T. pseudokoningii. Mycelial growth and the original pattern of protein synthesis resumed when the antagonists were removed. It is probable that volatile secondary metabolites have played an important role during the evolution of microorganisms in the context of community, population and functional dynamics.

Basidiomycota↗
PubMed2002

Low-virulence Citrobacter species encode resistance to multiple antimicrobials.

Citrobacter spp. are gram-negative commensal bacteria that infrequently cause serious nosocomial infections in compromised hosts. They are often resistant to cephalosporins due to overexpression of their chromosomal beta-lactamase. During a recent study of multidrug-resistant Enterobacteriaceae (MDRE) in solid-organ transplant patients, we found that almost half of patients colonized with MDRE carried one or more cefpodoxime-resistant Citrobacter freundii, Citrobacter braakii, or Citrobacter amalonaticus strains. Pulsed-field gel electrophoresis showed that 36 unique strains of Citrobacter were present among 32 patients. Genetic and phenotypic analysis of the resistance mechanisms of these bacteria showed that the extended-spectrum beta-lactamase (ESBL) SHV-5 or SHV-12 was encoded by 8 strains (26%) and expressed by 7 strains (19%). A number of strains were resistant to other drug classes, including aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%). PCR and DNA analysis of these multiresistant strains revealed the presence of class I integrons, including the first integrons reported for C. braakii and C. amalonaticus. The integrons encoded aminoglycoside resistance, trimethoprim resistance, or both. Despite the prevalence of MDR Citrobacter spp. in our solid-organ transplant patients, only a single infection with a colonizing strain was recorded over 18 months. Low-virulence Citrobacter spp., which can persist in the host for long periods, could influence pathogen evolution by accumulation of genes encoding resistance to multiple antimicrobial classes.

Citrobacter↗
PubMed1969

Organization of enzymes in the polyaromatic synthetic pathway: separability in bacteria.

ULTRACENTRIFUGATION IN SUCROSE DENSITY GRADIENTS WAS EMPLOYED TO ESTIMATE THE MOLECULAR WEIGHTS AND TO DETERMINE POSSIBLE PHYSICAL AGGREGATION OF THE FIVE ENZYMES CATALYZING STEPS TWO TO SIX IN THE PRECHORISMIC ACID PORTION OF THE POLYAROMATIC SYNTHETIC PATHWAY IN SIX SPECIES OF BACTERIA: Escherichia coli, Salmonella typhimurium, Aerobacter aerogenes, Bacillus subtilis, Pseudomonas aeruginosa, and Streptomyces coelicolor. The five enzymes were not aggregated in extracts of any of the species examined, nor are the genes encoding these enzymes clustered in those bacterial species for which genetic evidence exists. (An initial examination of the blue-green alga Anabaena variabilis indicates nonaggregation in this species also.) This situation in bacteria is in marked contrast to that found in Neurospora crassa and other fungi in which the same five enzymes are associated as an aggregate encoded (at least in the case of N. crassa) by a cluster of five genes. In addition, also in contrast to N. crassa, no evidence was obtained for more than one kind of dehydroquinase activity in any of the bacteria examined. These comparative results are discussed in relation to the origin, evolution, and functional significance of the gene-enzyme relationships existing in the early steps of aromatic biosynthesis in bacteria and fungi.

Alcohol Oxidoreductases↗
PubMed2006

Phylogenetic clustering and overdispersion in bacterial communities.

Very little is known about the structure of microbial communities, despite their abundance and importance to ecosystem processes. Recent work suggests that bacterial biodiversity might exhibit patterns similar to those of plants and animals. However, relative to our knowledge about the diversity of macro-organisms, we know little about patterns of relatedness in free-living bacterial communities, and relatively few studies have quantitatively examined community structure in a phylogenetic framework. Here we apply phylogenetic tools to bacterial diversity data to determine whether bacterial communities are phylogenetically structured. We find that bacterial communities tend to contain lower taxonomic diversity and are more likely to be phylogenetically clustered than expected by chance. Such phylogenetic clustering may indicate the importance of habitat filtering (where a group of closely related species shares a trait, or suite of traits, that allow them to persist in a given habitat) in the assembly of bacterial communities. Microbial communities are especially accessible for phylogenetic analysis and thus have the potential to figure prominently in the integration of evolutionary biology and community ecology.

Bacteria↗
PubMed1996

[Bacterial resistance and management of nosocomial infections: relations to hematology].

Because they receive many infected patients with various degrees of immunosuppression, the haematology departments have a high consumption of antibiotics. The possible relationship between antibiotic consumption and bacterial resistance is discussed in many specialities, especially for some classes like quinolones. This possible relationship has to be evocated in haematology where patients are at high risk of severe sepsis because of neutropenia. In Henri Mondor hospital, we studied the evolution of bacterial susceptibility and of antibiotic consumption in the haematology unit on a 6 year period. We found that this susceptibility was finally stable over time. The main factors which may influence the evolution of the bacterial susceptibility in our study, and in the literature are discussed.

4-Quinolones↗
PubMed1996

[Gastroenteritis due to Aeromonas in pediatrics].

OBJECTIVE: In recent years the incidence of gastroenteritis due to Aeromonas spp has increased significantly. The purpose of this study was to investigate the etiology and clinical manifestations of this disease. PATIENTS AND METHODS: In the period between 1986 and 1992, we found Aeromonas spp in seventy patients (88 samples) between 0 and 16 years of age. We were able to analyze 53 of these samples. RESULTS: Of all of the patients, 66% were males and 58.5% were younger than two years old. We found a pattern in the disease with 83% of the cases occurring in summer and autumn. The infection was polymicrobial in 43% of the patients. The clinical manifestations most often found were fever (71%), vomiting (62.5%) and abdominal pain (9.4%). Diarrhea was watery in 71.7% and 64% of the cases lasted less than a week. The number of stools was 5 to 10 per day in 58% of the patients. Forty patients (75.5%) required hospitalization, with the stay being longer than 10 days in 25%. There were 30% of the patients that required antibiotic therapy, mostly due to concomitant infections and not due to the diarrheic episodes, with all of them having a satisfactory evolution.

Acute Disease↗
PubMed2003

Evolutionary connections between bacterial and eukaryotic signaling systems: a genomic perspective.

Recent advances in microbial genomics suggest that several protein domains are common to bacterial and eukaryotic regulatory proteins. In particular, developmentally and morphologically complex prokaryotes appear to share several signaling modules with eukaryotes. New experimental studies and information from domain architectures point to several similar mechanistic themes in bacterial and eukaryotic signaling proteins. Laterally transferred protein domains, originally of bacterial provenance, appear to have contributed to the evolution of sensory pathways related to light, redox and nitric oxide signaling, and developmental pathways, such as Notch, cytokine and cytokinin signaling in eukaryotes.

Bacterial Physiological Phenomena↗