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Biomedical subjects

I Arana

Publications and source records attributed to I Arana.

11 recordsLinked to original sources
PubMed1999

Changes in DNA Content and Cellular Death during a Starvation-Survival Process of Escherichia coli in River Water.

Abstract Four nucleoid staining procedures were compared during the starvation-survival process of Escherichia coli in river water. Only the method performed as a modification of the standard acridine orange direct procedure allowed us to visualize nucleoids during the 95 days of experimentation. Moreover, with this method the total number of cells and nucleoid-containing cells can be simultaneously enumerated. The decrease of the chromosomal DNA content of population and of the nucleoid-containing cells indicates that ghosts form and cellular death occurs throughout the starvation-survival process. A long time (<30 days) is needed for non-nucleoid-containing cells to appear in river water; plasmid DNA is also negatively affected by environmental stress. After 4 days of storage in river water, the need to increase the volume of lysed cells used for the plasmid band visualization as well as the decrease in the plasmid band intensity would indicate a decrease in the plasmid DNA content during the starvation-survival process. According to our results, both chromosomal and plasmid DNA content decrease during the starvation-survival process of E. coli in river water.

Journal Article↗
PubMed1999

Chlorination and ozonation of waste-water: comparative analysis of efficacy through the effect on Escherichia coli membranes.

The effect of chlorine and ozone on Escherichia coli cells resuspended in waste-water was compared. Selected chlorination and ozonation conditions produced a similar decrease in culturability (2-2.5 log). Under these conditions, differences in membrane permeability and cell surface hydrophobicity, depending on the disinfectant tested, were detected. After ozonation, while no changes in cell surface hydrophobicity were observed, approximately 95.5% of cells showed altered membrane permeability. The effect of chlorine was not linked to changes in membrane permeability. After chlorination, E. coli cells showed a tendancy to aggregate. The possibility that aggregation of cells could interfere with conventional colony counts is discussed. The degree of toxicity (Microtox assay) was unrelated to the effect on cellular activity.

Cell Membrane Permeability↗
PubMed1998

Discharge of disinfected wastewater in recipient aquatic systems: fate of allochthonous bacterial and autochthonous protozoa populations.

The discharge of disinfected effluents affects the bacterivorous ability of protozoa and the effect depends on the disinfectant applied. Chlorine provokes a decrease in the number of protozoa and a delay in the bacterivorous ability. The discharge of ozonated and peracetic acid-treated wastewater provokes only an initial slight decrease in bacterivorous ability. No correlation was found between toxicity values detected using the Microtox assay and the effect of disinfected effluents on freshwater protozoa population. After the disinfection processes, recipient systems (fresh and marine water) have different effects on the survival of Escherichia coli populations discharged to them. The effect of the freshwater recipient system is less negative than the effect provoked by sea-water, and the differences detected depend on the disinfection treatment applied. The wastewater bacterial population as a whole is able to grow after discharge of disinfected wastewater to receiving waters. However, in the absence of predation or competition, the recipient systems exert selection, with rod-shaped bacteria predominating.

Animals↗
PubMed1997

A process-oriented reasoner about physiology.

This paper presents the RAP system: a reasoner about physiology. RAP performs two tasks: (1) it infers the behaviour of a complex physiological process using the behaviours of its subprocesses and the relationships between them; (2) it reasons about the effect of introducing a fault into the model. In order to reason about the behaviour of a complex process, RAP uses a mechanism which: (i) represents how subprocesses behave; (ii) establishes how these subprocesses affect each others behaviors; (iii) 'aggregates' these behaviors together to obtain the behavior of the top level process; (iv) gives that process a temporal context in which to act. RAP uses limited common sense knowledge about faults to reason about their effect in terms of the generation of new processes and the misbehavior of existing ones. The effects are then propagated throughout the model to obtain the overall effect of the fault.

Artificial Intelligence↗
PubMed1997

Detection and enumeration of viable but non-culturable transconjugants of Escherichia coli during the survival of recipient cells in river water.

Viable but non-culturable transconjugant cells were detected by a modification of the direct viable count (DVC) method. This modification involved the addition of parental antimicrobial markers (kanamycin and streptomycin) to the elongation medium in order to promote selective elongation of the transconjugant cells. Presence of viable, other than culturable, transconjugants was demonstrated in matings with parental cells from TSB culture as well as with recipient cells from survival in river water (under illuminated and non-illuminated systems). In matings with a recipient strain from illuminated systems, culturable transconjugants were not detected after the third day of recipient cell survival. In spite of this, viable transconjugants were detected in numbers that exceeded 10(5) cells ml-1. These results clearly show that a fraction of non-culturable recipient cells is able to receive and express plasmids by conjugation processes and form viable but non-culturable transconjugant cells.

Ciprofloxacin↗
PubMed1995

Disinfectant tolerance and antibiotic resistance in psychrotrophic gram-negative bacteria isolated from vegetables.

A total of 330 strains of psychrotrophic non-fermenting Gram-negative bacteria isolated from vegetables were studied. In spite of the wide range of antibiotic resistance occurring, less than 10% showed resistance patterns which included mezclocillin-ticarcillin-gentamicin or ceftizoxime-norfloxacin. Reductions of > 5 log10 in the numbers of cfu were found when these strains were exposed for 30 min to a quaternary ammonium compound (1% w/v).

Colony Count, Microbial↗
PubMed1994

Effect of growth phase and parental cell survival in river water on plasmid transfer between Escherichia coli strains.

We evaluated the transfer to and from Escherichia coli of endogenously isolated plasmid material from the River Butrón during the growth of three donor strains and two recipient strains as well as after the survival of these parental cells in river water. Transfer frequency varied greatly during the growth of donor cells, with minimum values in the exponential phase; frequency remained constant, however, during the growth of recipient strains. After survival in river water, donor cells lost their ability for plasmid transfer before any other physiological variations in the cells caused by environmental stress were detected. Under the same conditions and during equal periods, however, no variation in the ability of recipient cells to receive and express plasmid material was observed.

Colony Count, Microbial↗
PubMed1992

Survival strategies of plasmid-carrier and plasmidless Escherichia coli strains under illuminated and non-illuminated conditions, in a fresh water ecosystem.

A comparative study, in illuminated and non-illuminated systems, was made to determine the survival strategies of plasmid-carrier and plasmidless bacteria in sterile river water. Two strains of Escherichia coli from river water were selected: one plasmidless, EC1, and one antibiotic-resistant strain, EC7, which showed plasmid bands. By matings with EC7 as donor and E. coli K12 strain J62 as recipient, transconjugants were generated, the J62(7) strain, which showed both antibiotic resistance and plasmid bands. Ethidium bromide curing of the EC7 strain generated the EC7(2) strain which showed a partial loss of resistance and a reorganization of plasmid bands. Under non-illuminated conditions the total number of cells detected by direct count and the number of culturable cells (injured and non-injured cells) remained practically constant throughout the period of incubation. In the illuminated systems, however, the number of cfu decreased in four of the five strains studied. The greatest decreases are those of the J62 strain, followed by those of the J62(7), EC1, EC7(2) and EC7 strains. Differences in survival strategies as a consequence of the presence or absence of plasmids are discussed.

Colony Count, Microbial↗
PubMed1992

Role of hydrogen peroxide in loss of culturability mediated by visible light in Escherichia coli in a freshwater ecosystem.

A study was made of the mechanisms by which visible light produces cell dormancy in Escherichia coli, resulting in loss of culturability. Visible light may act directly on the cells or generate photoproducts with a negative effect on the cells. In nonilluminated microcosms the addition of increasing concentrations of hydrogen peroxide, one of the photoproducts formed in natural aquatic systems, gave rise to the formation of nonculturable cells and injured culturable cells, and this negative effect depended on the concentration of peroxide. On the other hand, in illuminated microcosms the addition of compounds which eliminate hydrogen peroxide (i.e., catalase, sodium pyruvate, and thioglycolate) had a protective effect on the E. coli cells, as the CFU counts on minimal medium and on recuperation medium were significantly higher (P < 0.05) than those detected in the absence of these compounds. Furthermore, when hydrogen peroxide was eliminated, the CFU counts on recuperation medium did not fall significantly, indicating that nonculturable cells did not form. These results rule out the direct effect of visible light on the cells and show that hydrogen peroxide, generated photochemically, may be the cause of the loss of culturability of E. coli in illuminated systems.

Colony Count, Microbial↗
PubMed1986

Influence of light and natural microbiota of the Butrón river on E. coli survival.

The survival of an E. coli strain in water samples from the Butrón river has been studied. The input of E. coli cells in the aquatic system breaks down the established balance among the components of the natural microbiota: E. coli becomes the object of the active protozoal predation whereas the autochtonous heterotrophic community become alternative preys. As a result of this new situation, the natural microbiota increases but returns to the initial values once the E. coli cells have been removed from the system. The effect of the temperature of incubation on the survival is exerted through the effect of this parameter on the predatory activity of the protozoa. Light has a lethal and direct action on the E. coli cells, the effect of this parameter is even superior to that of predation.

Animals↗