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Biomedical subjects

M J Gauthier

Publications and source records attributed to M J Gauthier.

34 records · Page 2Linked to original sources
PubMed1989

Influence of osmoregulation processes on starvation survival of Escherichia coli in seawater.

The adaptation of enteric bacteria in seawater has previously been described in terms of nutrient starvation. In the present paper, we bring experimental arguments suggesting that survival of these microorganisms could also depend on their ability to overcome the effects of osmotic stress. We analyzed the influence of osmoregulatory mechanisms (potassium transport, transport and accumulation of organic osmolytes) on the survival of Escherichia coli in seawater microcosms by using mutants lacking components of the osmotic stress response. Long-term protection was afforded to cells by growth in a medium whose osmotic pressure was increased by either NaCl, LiCl, or saccharose. Achievement of the protection state depended at least partly on osmoregulatory mechanisms, but differed when these were activated or induced during prior growth or in resting cells suspended in phosphate buffer or in seawater. When achieved during growth, K+ transport, glycine-betaine (GBT) synthesis or transport, and trehalose synthesis helped increase the ability to survive in seawater. Protection by GBT was also obtained with resting cells in a phosphate buffer at high osmotic pressure. However, when added only to the seawater, GBT did not change the survival ability of cells no matter what their osmoregulation potential. These results showed that the survival of E. coli cells in seawater depends, at least partly, on whether they possess certain genes which enable them to regulate osmotic pressure and whether they can be stimulated to express those genes before or after their release into the environment. This expression requires nutrients as the substrates from which the corresponding gene products are made.

Culture Media↗
PubMed1989

Influence of prior growth conditions on low nutrient response of Escherichia coli in seawater.

By use of experimental microcosms, it was demonstrated that the survival of Escherichia coli in nutrient-free seawater depended on the age of cells and on some physicochemical conditions during their prior growth. Cells grown in a bacteriological medium, with an acid or an alkaline pH, at high temperature (44 degrees C), or in the absence of oxygen were more sensitive to exposure to seawater of low nutrient content. In contrast, some complex media allowed production of cells adapting more rapidly to seawater. Cells grown in urine were far more sensitive than those grown in all bacteriological media tested. The sensitivity of all cells was highest when they were harvested during the early exponential phase of growth.

Anaerobiosis↗
PubMed1989

[Modification of the envelope and the protein content of Escherichia coli surviving in sea water].

A toxigenic strain of Escherichia coli displayed important structural modifications when placed in seawater which naturally lacked nutritive elements, as observed by electron microscopy. These include cell wall and cell body distortion, modification of the membranes, central segregation of the chromosome, and retraction of the cytoplasm. These modifications were accompanied by a decrease in cell protein content of approximately 40%. Certain cytoplasmic membrane proteins were lost, and new ones appeared. The development of these changes was considerably slower in cells that had previously been grown in a seawater medium. This suggests that osmotic regulation mechanisms, which enable E. coli to survive much longer in marine conditions, may have a protective influence.

Bacterial Proteins↗
PubMed1987

Changes in Escherichia coli cells starved in seawater or grown in seawater-wastewater mixtures.

Some metabolic modifications of Escherichia coli cells during starvation in seawater were studied in laboratory microcosms. The apparent die-off of this bacterium under such conditions, as observed by comparing the enumeration of CFU in conventional freshwater media and direct epifluorescence counts, was partially prevented when cells were previously grown in salted organic medium or on seawater-wastewater agar. beta-Galactosidase activity of starved cells disappeared gradually with time, even though some other enzymatic activities, such as that of alkaline phosphatase, increased. Moreover, some modifications of sensitivity to antibiotics, heavy metals, and bacteriophages in seawater- and wastewater-grown cells suggested that the cells undergo structural changes under natural marine conditions. These results provide additional experimental data indicating the possible active adaptation of E. coli cells to seawater.

Alkaline Phosphatase↗
PubMed1985

Influence of salts and temperature on the transfer of mercury resistance from a marine pseudomonad to Escherichia coli.

Thirty-one strains of marine bacteria were examined for their ability to transfer mercury resistance to Escherichia coli in complex media; eight strains were able to transfer their resistance marker, with frequencies ranging from 10(-3) to 10(-8). Frequencies generally increased with the increase of the mating period. Additional mating experiments were carried out with one strain, belonging to the pseudomonads, to estimate the influence of temperature, salinity, and time on the conjugal transfer frequency of mercury resistance markers. The higher frequencies occurred at 30 degrees C, in a salt medium (37%), after 24 h of mating.

Conjugation, Genetic↗
PubMed1979

New prodigiosin-like pigment from Alteromonas rubra.

The red prodigiosin-like pigment from Alteromonas rubra was shown to be a mixture of prodigiosin (pigment 1) and a new cyclic isomer (pigment 2). The new structure was elucidated by mass and nuclear magnetic resonance spectra. Careful examinations of the prodigiosins produced by Serratia marcescens, Vibrio psychoerythrus, and an unidentified red bacterium (LL-100-6) failed to disclose any of the new pigment, pigment 2.

Bacteria↗
PubMed1979

[Experimental study of vibrio parahaemolyticus (biotype 2) transfer from water and sediments to benthic marine food chain organisms].

Transfer of Vibrio parahaemolyticus (biotype 2) from sediments to water and from water to benthic marine organisms was studied experimentally using a streptomycin-resistant strain. Transmission by trophic pathways was also studied using reconstituted marine food chains (Mytilus edulis, Nereis diversicolor, Carcinus maenas, Scorpaena porcus, Mus musculus). Water colonization by sediments could be observed only at temperatures above 16 degrees C. Sediments could well constitute a disseminating reservoir for these germs, their cycle in water being dependent of the cycle followed in the sediments. Contamination of animal organisms is essentially effected by a direct mean, either water or sediments; transfer by trophic pathways being negligible. Infection of land consumers (mice) is linked quantitatively to the nature of the last marine organism of the food chain since bacteria can flourish in the digestive tract of certain animals (Carcinus maenas).

Animals↗
PubMed1978

[Production of a photo-sensitive lipid antibiotic by the marine diatom Chaetoceros lauderi (Ralfs) (author's transl)].

A lipid antibiotic was extracted from whole cells of the marine diatom Chaetoceros lauderi (Ralfs) and roughly identified as an unsaturated fatty acid by thin layer chromatography. A number of Gram-positive terrestrial bacteria and several Gram-negative marine bacilli were sensitive to this antibiotic, whereas Gram-negative enteric bacteria were resistant. Solar irradiation led to its partial disappearance and to the production of more polar antibiotics with a stronger antibacterial activity. This observation is compared to similar data culled from literature, and its significance in a natural environment is discussed.

Anti-Bacterial Agents↗
PubMed1976

Modification of bacterial respiration by a macromolecular polyanionic antibiotic produced by a marine Alteromonas.

A macromolecular polyanionic antibiotic produced by a marine bacterium belonging to the genus Alteromonas causes a large modification in bacterial respiration when added to the culture of several bacterial species in their early stage of growth. This antibiotic induces an increase of oxygen uptake and the production of hydrogen peroxide. The latter fact explains the high sensitivity of bacteria with low catalase activity and the antagonistic effect of pure catalase on antibiosis. The antibiotic could act at the level of the respiratory chain by setting up a flavinic respiration.

Anti-Bacterial Agents↗
PubMed1976

Morphological, physiological, and biochemical characteristics of some violet-pigmented bacteria isolated from seawater.

Sixteen violet-pigmented heterotrophic bacilli were isolated from Mediterranean coastal waters. Morphological and physiological studies showed that they have a number of characteristics specific to the genus Chromobacterium. However, the absence of catalase, the presence of oxidase, and, more especially, the low percentage of bases guanine and cytosine in their DNA exclude them from the genus. The specificity of some characters assigned to Chromobacterium can thus be discussed. Several features allow us to consider such bacteria as being related to the genus Alteromonas; their consistency within the 16 strains investigated leads us to consider them as a single species, for which the specific name Alteromonas luteo-violaceus (sp. nov.) is proposed.

Bacteria↗
PubMed1976

Antibacterial activity of marine violet-pigmented Alteromonas with special reference to the production of brominated compounds.

The synthesis of several types of antibiotics was investigated in four strains of violet-pigmented bacteria belonging to the species Alteromonas luteo-violaceus. Two of the strains simultaneously produce an antibiotic polyanionic polysaccharide, weakly bound to the cells and diffusing throughout the medium, and two intracellular brominated bactericidal substances. The third strain only synthesizes the polyanionic antibiotic. The fourth one is totally inactive. The macromolecular antibiotic, probably responsible for the autointoxication of the bacteria in their cultures, acts at the respiratory level; it induces an increase of oxygen uptake and the production of peroxides by test bacteria. Thus, its activity is inhibited by catalase and peroxidase.

Anti-Bacterial Agents↗
PubMed1975

Taxonomic position and seasonal variations in marine neritic environment of some gram-negative antibiotic-producing bacteria.

Six marine bacteria which synthesize macromolecular antibiotics were isolated from neritic waters on the French Mediterranean coast, and their frequency recorded over two successive years. They appeared in relatively large numbers during the period August to December, and can be identified as marine pseudomonads; however, the low guaninecytosine ratio of their DNA, lack of catalase and specific self-inhibition are not compatible with the characteristics of the genus Pseudomonas. Two produced violacein, usually synthesized by bacteria belonging to the genus Chromobacterium. Their taxonomic position is discussed.

Anti-Bacterial Agents↗
PubMedDate not supplied

The immunophenotype of peripheral blood lymphocytes in clinically healthy dogs and dogs with lymphoma in remission.

Lymphoma is a common cancer of dogs that frequently is treated with chemotherapy or radiation therapy. Response to therapy is variable and currently available diagnostic tests do not reliably predict response to therapy. Treatment for lymphoma often results in lymphopenia, but it is unknown whether the changes in circulating lymphocytes result from generalized or specific reduction of lymphocytes. In this study, blood lymphocytes from 12 clinically healthy dogs, 10 dogs in remission because of treatment for B-cell lymphoma, and 8 dogs in remission from T-cell lymphoma were analyzed by flow cytometry by using a panel of 20 antibodies reactive with canine leukocyte antigens. Results identified similar lymphocyte parameters in treated dogs regardless of the type of lymphoma. Treated dogs had >50% reduction in blood lymphocyte concentration, and an absolute decrease in most subsets of lymphocytes. Both groups of treated dogs had relative increases in the proportion of CD3+, T-cell receptor (TCR)alphabeta+, and CD90+ lymphocytes, and a decreased proportion of CD45RA+ cells. In addition, dogs with T-cell lymphoma in remission had a significant increase in the proportion of CD49d+ lymphocytes. These findings were interpreted as representing likely suppression of lymphocyte regeneration by chemotherapy, with a relative increase in the proportion of memory over naive lymphocytes. Lack of correlation with the T- or B-cell origin of the initial lymphoma suggested that, by using flow cytometric methods, residual circulating neoplastic cells could not be detected. However, the changes in the lymphocyte profile of dogs treated with chemotherapy may have relevance to their immunocompetence.

Animals↗
PubMedDate not supplied

[Numeration of bacteria in seawater: variability and dubiousness (author's transl)].

Authors tried to determine some factors of incertitude in the anlaysis of the bacterial contamination of seawater. Such analysis depends on the reliability of the methods used for bacterial numeration, and on the heterogeneity of water in the investigated area. The general numeration of organisms (GNO) and the numeration of coliforms (NC) were taken into account. The turbidity of the sample, and the operator's manner were shown to be factors of variation for the GNO. An interaction between the operator and the amount of the anlaysed sample seemed to influence NC. In a natural environment, variations with time were the most important. They were partly due to hydrological and meteorological fluctuations, but sometimes seemed to be random. During a day cycle, the bacterial contamination trended to decrease when the solar radiance was maximum. Influence of short scale variations in the location of sampling was generally random, yet with a slight increase of contamination in the more stagnant waters.

Analysis of Variance↗