Biomedical subjects

R Guerrero

Publications and source records attributed to R Guerrero.

At least 91 records · Page 5Linked to original sources

PubMed1992

Failure of a synthetic vaccine to protect Aotus lemurinus against asexual blood stages of Plasmodium falciparum.

The hybrid synthetic protein SPf(66), which contains small fragments of the 83-kD, 55-kD, 35-kD, and circumsporozoite antigens of Plasmodium falciparum, was studied to determine its protective capacity against malaria infection in Aotus lemurinus monkeys. Two groups of six monkeys each were immunized six times with this polymer, which was mixed with either Freund's adjuvant or aluminum hydroxide. Two groups of five animals each were used as controls and immunized with saline solution mixed with the same adjuvants. Neither antipeptide nor antimalarial antibodies developed after the six immunization doses. Regardless of this fact, the monkeys were challenged intravenously with 10(5) P. falciparum blood stage parasites, and the resultant parasitemia was followed daily on blood smears. Only one monkey from each of the groups immunized using Freund's adjuvant (both experimental and control) was protected. In those immunized using aluminum hydroxide, one animal was protected in the experimental group, but none were protected in the control group. Anti-parasite antibodies developed during the infection, but did not correlate with protection and failed to recognize SPf(66) peptide in an enzyme-linked immunosorbent assay. Immunization with the polymer did not boost natural antibodies present in two of the monkeys before the experiment. Low levels of gamma-interferon were produced in some animals, but were not correlated with protection.

Amino Acid Sequence↗

PubMed1991

Kingdoms in turmoil.

How should the world's living organisms be classified? Into how many kingdoms should they be grouped? Scientists have been grappling with these questions since the time of Aristotle, drawing on a broad base of biological characteristics for clues. The fossil record, visible traits of living organisms and, more recently, results from cell biology have all shaped theories of biological classification. But last year a new and controversial concept emerged: a classification of life based solely on molecular traits. The focal point of the controversy is a tree of life, or "phylogeny", devised by Carl Woese of the University of Illinois, Otto Kandler of the University of Munich and Mark Wheelis of the University of California. The tree is unusual because, unlike all previous schemes, it is constructed solely from biochemical data such as DNA sequences rather than a range of different organism characteristics. But that is not all. The scheme also challenges the idea that life on Earth is best divided into five kingdoms, with the main split being between bacteria and all other organisms. Woese and his colleagues create three main groupings by dividing the bacteria in two and unifying all other organisms.

Animals↗

PubMed1990

Mobilifilum chasei: morphology and ecology of a spirochete from an intertidal stratified microbial mat community.

Spirochetes were found in the lower anoxiphototrophic layer of a stratified microbial mat (North Pond, Laguna Figueroa, Baja California, Mexico). Ultra-structural analysis of thin sections of field samples revealed spirochetes approximately 0.25 micrometer in diameter with 10 or more periplasmic flagella, leading to the interpretation that these spirochetes bear 10 flagellar insertions on each end. Morphometric study showed these free-living spirochetes greatly resemble certain symbiotic ones, i.e., Borrelia and certain termite spirochetes, the transverse sections of which are presented here. The ultrastructure of this spirochete also resembles Hollandina and Diplocalyx (spirochetes symbiotic in arthropods) more than it does Spirochaeta, the well known genus of mud-dwelling spirochetes. The new spirochete was detected in mat material collected both in 1985 and in 1987. Unique morphology (i.e., conspicuous outer coat of inner membrane, large number of periplasmic flagella) and ecology prompt us to name a new free-living spirochete.

Animals↗

PubMed1989

Variations in cell size and buoyant density of Escherichia coli K12 during glycogen accumulation.

The effect of glycogen accumulation on buoyant density and volume of Escherichia coli K12 was studied. A procedure consisting of three linear equations is presented. This requires measurement only of three parameters: cell buoyant density, cell volume and specific content of the polymer. Experimental values are then used to calculate intercepts and slopes of the equations by linear regression. From the estimated values of such parameters the in vivo values of several variables of interest can be calculated. These include in vivo density and volume of the glycogen inclusion, as well as density and volume of the structural material in the cell. The results are consistent with the glycogen inclusions being hydrated.

Escherichia coli↗

PubMed1989

Contact phase of blood coagulation in cardiogenic pulmonary oedema (CPO) and adult respiratory distress syndrome (ARDS).

In order to assess the role of the kallikreinkinin (k-k) system in the pathogenesis of pulmonary oedema, we studied the contact phase factors of blood coagulation, as well as the haemodynamics and blood gas changes in 34 patients with pulmonary oedema, 23 of them with Adult Respiratory Distress Syndrome (ARDS) and 11 with cardiogenic pulmonary oedema (CPO). We have verified significant differences in the haemodynamic pattern and blood gases between the two groups of patients, which corroborate the previously established differences between both types of pulmonary oedema. Our results reveal k-k system activation in ARDS patients, with a significant fall in factor XII (p less than 0.05), prekallikrein (p less than 0.01), alpha-2-macroglobulin (p less than 0.01) and high molecular - weight kininogens (p less than 0.005), with a rise in C1-esterase inhibitor (p less than 0.001) in comparison with patients with CPO. All of the CPO patients had normal prekallikrein levels, whereas 15 out 23 ARDS cases (65%) had decreased prekallikrein values. Our results suggest that the k-k system activation could play a role in the pathogenesis of ARDS. Estimation of prekallikrein levels may be helpful in the differential diagnosis of ARDS.

Adult↗

PubMed1989

Acute invasive diarrhea in the pediatric patient.

In acute invasive diarrhea, the pathogen penetrates the epithelial cells of the intestinal mucosa. Symptoms are produced by one or more of the following mechanisms: production of enterotoxins, increased synthesis of prostaglandins, and impaired reabsorption of fluids and electrolytes. The invasive process often results in dysentery, which is characterized by watery stools containing blood and mucus, accompanied by cramps, rectal burning, fever, and, sometimes, toxicity. Among the complications are bacteremia and toxic megacolon. Diagnosis is based on the patient's clinical condition and examination of stools. Microscopic examination of stools can rule out parasites and detect leukocytes, particularly polymorphonuclear leukocytes, a finding that suggests a bacterial origin for the disease. Because most patients are not severely dehydrated, rehydration is not the mainstay of treatment; in most cases, fluids can be replaced orally. Absorbents are ineffective, and antiperistaltic drugs should not be used routinely in children. Although often unnecessary in simple cases of invasive diarrhea, antimicrobials are useful when risk factors related to age, clinical condition, malnourishment, dehydration, or underlying disease are present. In such cases, antimicrobial therapy should begin when the clinical diagnosis has been made, to ensure the best clinical response.

Bacterial Infections↗

PubMed1989

Isolation of a high frequency donor of Rhodobacter capsulatus by integration of the plasmid pMT1000 into the chromosome.

The temperature-independent clone of Rhodobacter capsulatus UA7041, carrying the temperature-sensitive plasmid pMT1000, has been obtained by selection for plasmid markers at the non-permissive temperature. The transfer to Escherichia coli of all drug resistance encoded by pMT1000 was of about 10(-7) when the donor was the UA7041 strain, and of 5 x 10(-4) when the donor was the temperature-sensitive strain of R. capsulatus. Electrophoretic analyses showed no plasmid band typical of the autonomous pMT1000 in the UA7041 strain. Furthermore, UA7041 cells were also able to mobilize chromosomal markers of R. capsulatus at a frequency of about 10(-4) per donor cell. All these results lead us to conclude that the plasmid pMT1000 is integrated in the chromosome of the UA7041 strain. The analysis of the co-transfer frequencies of trp and his markers has shown that the chromosome mobilization in the UA7041 strain of R. capsulatus is unidirectional from a single origin. Our data also show that the pMT1000 plasmid may be useful to the construction of chromosomal, high-frequency donor strains.

Bacteria↗

PubMed1988

Increase in plasmid transformation efficiency in SOS-induced Escherichia coli cells.

UV irradiation of competent cells of Escherichia coli K12 produced an increase in the efficiency of transformation with plasmid DNA. This phenomenon has been called IPTE (increase in plasmid transformation efficiency) and is dependent on the activated state of the RecA protein. IPTE is independent of the lexA, recB recC, and recF genes. It is not related to the size or the replicon type of the plasmid. Furthermore, it is also induced in cells which have been previously treated with other SOS system-inducing agents such as bleomycin, mitomycin C, or nalidixic acid. IPTE is therefore similar to other repair (SOS) functions inducible by DNA damage since all of them are dependent upon activation of the RecA protein. IPTE differs from other SOS functions in the absence of a direct control by the LexA repressor.

DNA Repair↗

PubMed1988

The evolutionary transition from RNA to DNA in early cells.

The evolution of genetic material can be divided into at least three major phases: first, genomes of "nucleic acid-like" molecules; secondly, genomes of RNA; and finally, double-stranded DNA genomes such as those present in all contemporary cells. Using properties of nucleic acid molecules, we attempt to explain the evolutionary transition from RNA alone as a cellular informational macromolecule prior to the evolution of cell systems based on double-stranded DNA. The idea that ribonucleic acid-based cellular genomes preceded DNA is based on the following: (1) protein synthesis can occur in the absence of DNA but not of RNA; (2) RNA molecules have some catalytic properties; (3) the ubiquity of purine and pyridine nucleotide coenzymes as well as other similar ribonucleotide cofactors in metabolic pathways; and (4) the fact that the biosynthesis of deoxyribonucleotides always proceeds via the enzymatic reduction of ribonucleotides. The "RNA prior to DNA" hypothesis can be further developed by understanding the selective pressures that led to the biosynthesis of deoxyribose, thymine, and proofreading DNA polymerases. Taken together these observations suggest to us that DNA was selected as an informational molecule in cells to stabilize earlier RNA-protein replicating systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Evolution↗

PubMed1988

Inhibition of the SOS response of Escherichia coli by the Ada protein.

Induction of the adaptive response by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) caused a decrease in the UV-mediated expression of both recA and sfiA genes but not of the umuDC gene. On the other hand, the adaptive response did not affect the temperature-promoted induction of SOS response in a RecA441 mutant. The inhibitory effect on the UV-triggered expression of the recA and sfiA genes was not dependent on either the alkA gene or the basal level of RecA protein, but rather required the ada gene. Furthermore, an increase in the level of the Ada protein, caused by the runaway plasmid pYN3059 in which the ada gene is regulated by the lac promoter, inhibited UV-mediated recA gene expression even in cells to which the MNNG-adaptive treatment had not been applied. This inhibitory effect of the adaptive pretreatment was not observed either in RecBC- strains or in RecBC mutants lacking exonuclease V-related nuclease activity. However, RecF- mutants showed an adaptive response-mediated decrease in UV-promoted induction of the recA gene.

Alkylation↗

PubMed1987

Induction of the SOS response by hydroxyurea in Escherichia coli K12.

Hydroxyurea at concentrations higher than 10(-2) M induced the recA and sfiA genes of E. coli as well as the lambda prophage by a pathway independent of the recBC genes. In addition, the hydroxyurea-mediated induction of the SOS response is accompanied by a recA-dependent decrease on the cellular ATP pool. The presence of the multicopy plasmid pPS2, harboring the nrdAB genes (encoding the ribonucleoside reductase enzyme), abolished the hydroxyurea-induced expression of the recA gene. These data lead us to suggest that induction of the SOS response by hydroxyurea is due to the blocking of DNA replication by the inhibition of the ribonucleoside reductase complex activity.

Bacterial Proteins↗

PubMed1987

Influence of S9 mix in the induction of SOS system by quercetin.

The induction of recA, umuC and sfiA genes by quercetin was studied in the presence and in the absence of S9 mix. The inducing activity of quercetin is higher for sfiA than for recA and umuC genes in the absence of S9 mix. The putative genotoxic metabolites of quercetin produced by S9 mix display different inducing activities of the three SOS genes as compared to quercetin. The induction of sfiA gene is decreased by the presence of S9 mix, whereas an opposite effect was observed concerning umuC and recA. These data suggest that the error-prone repair pathway participates in mutagenesis by quercetin and its metabolites. Moreover, the type of DNA damage exerted by quercetin seems to be determined by its metabolic fate. The importance of testing for the induction of other SOS genes, together with sfiA, in the study of SOS functions as a genotoxic index is emphasized.

Animals↗

PubMed1987

DNA repair systems in the phototrophic bacterium Rhodobacter capsulatus.

UV irradiation and mitomycin C exposure trigger a protease-activity-dependent inhibition of cell division in Rhodobacter capsulatus, which begins about 2 h after the treatment is applied. UV irradiation also induces a dose-dependent mutagenesis with a maximal rate between 5 and 10 J m-2, with increased synthesis of a protein of Mr approximately 30,000 between 2 and 3 h after UV irradiation. In addition, R. capsulatus has an efficient photoreactivation system that reverses the lethal effects of UV irradiation in the presence of intense visible light.

Cell Division↗

PubMed1987

Modulating action of cyclic AMP on the expression of two SOS genes in Escherichia coli K-12.

Ultraviolet irradiation and cyclic AMP treatment produce a synergistic effect on the induction of the cle1 gene (coding for bacteriocin ColE1) in wild-type strains of Escherichia coli. On the other hand, cyclic AMP does not affect the uv-mediated induction of the recA, sfiA, and umuDC genes. Growth in the presence of glucose or glycerol does not affect the factor of amplification of the expression of the cle1 gene in uv-irradiated cells of the wild-type strain. Although, in cultures not treated with uv, the basal level of cle1 induction is about twice as high in cell grown grown with glycerol as in those using glucose as carbon source. In recA mutants neither simultaneous nor separate treatments with either cyclic AMP or uv irradiation induced transcription of the cle1 gene. Moreover, cyclic AMP induced a slight increase in cle1 gene expression in uv-irradiated cya strains, but not in the crp mutants. Nevertheless, the pattern of the uv-mediated induction of other SOS genes, such as umuDC, was the same in the cya and crp mutants, as in their parental wild-type strains. Furthermore, the uv-mediated induction of lambda prophage was decreased after either addition of cyclic AMP or growth in cultural conditions where the level of this nucleotide was low.

Bacteriophage lambda↗

PubMed1986

Behaviour of the contact phase of blood coagulation in the adult respiratory distress syndrome (ARDS).

In order to assess the role of the kallikrein-kinin (K-K) system in the pathogenesis of the adult respiratory distress syndrome (ARDS) we have prospectively determined coagulation contact phase, blood gas and hemodynamic parameters in patients with ARDS at 0, 36 and 72 h from diagnosis. Compared to normal values, significantly lower mean levels of factor XII (71.4 +/- 9.8%, p less than 0.0005), prekallikrein (PPK) (52 +/- 5.7%, p less than 0.0005), high molecular weight kininogen (HMWK) (73 +/- 2%, p less than 0.0005) and alpha 2-macroglobulin (alpha 2-M) (51 +/- 7.1%, p less than 0.0005) were found in ARDS patients. The functional kallikrein inhibitory activity (KKI) and C1-esterase inhibitor antigenic (CIINH) were significantly higher in these patients (113.2 +/- 5, p less than 0.005 and 124.7 +/- 7.6, p less than 0.0005 respectively) compared with normal values during the entire study period. The KKI/CIINH ratio decreased significantly in our ARDS patients at 0, 36 and 72 h (p less than 0.025; p less than 0.05 and p less than 0.005 respectively). We found a significant correlation between PPK levels and oxygenation index (r = 0.69, p less than 0.001), PPK and the static thoracic compliance values (r = 0.64, p less than 0.001). There was also a significant correlation between PPK levels and Qs/Qt (r = -0.89, p less than 0.001). ARDS patients that survived presented a stability in the PPK values in successive tests. Nevertheless non-survivors showed a progressive decrease in PPK levels during the follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Induction of SOS genes of Escherichia coli by chromium compounds.

The induction of several SOS genes of Escherichia coli such as recA, umuC, and sfiA by hexavalent (K2Cr2O7, K2CrO4, and CrO3) and trivalent (CrCl3, Cr(NO3)3, and (CH3COO)3Cr) compounds of chromium was studied. Induction was measured as beta-galactosidase activity, using lacZ gene fusions under the control region of different SOS genes. The hexavalent chromium forms induced the genes responsible for massive synthesis of RecA protein, error-prone repair, and inhibition of cell division. On the other hand, the trivalent chromium compounds were unable to induce any of the SOS genes tested. Individual assay of hexavalent chromium compounds showed that K2Cr2O7 was a stronger inducing agent of those three SOS genes tested than K2CrO4, which, in turn, was stronger than CrO3. All this data led to the conclusion that hexavalent chromium compounds, but not trivalent, are proficient agents of induction of the SOS system and can produce indirect mutagenesis in Escherichia coli.

Cell Division↗

PubMed1986

Expression of the SOS system in Escherichia coli growing under nitrate respiration conditions.

Induction of several SOS functions by mitomycin C, bleomycin or thermal treatment of a recA441 mutant growing under nitrate respiration conditions was studied in Escherichia coli. Mitomycin C caused inhibition of cell division, induction of prophages and expression of umuC gene but like in aerobically growing cells, it did not trigger the cessation of cell respiration. On the contrary, both recA+ and recA441 cultures either treated with bleomycin or incubated at 42 degrees C failed to induce any of the different SOS functions cited above. Furthermore, after bleomycin addition or thermal treatment both recA+ and recA441 cultures did not present any variation in the cellular ATP level, contrary to what happens under aerobic growth. The blocking of the expression of some SOS functions under nitrate respiration conditions is not an irreversible process because cells incubated under these anaerobic conditions were able to induce the SOS system when changed to an aerobic medium 30 min after the SOS-inducing treatment had been applied.

Adenosine Triphosphate↗

PubMed1986

5-Azacytidine: survival and induction of the SOS response in Escherichia coli K-12.

Survival and induction of the SOS system by 5-azacytidine, an analog of cytidine, were studied in Escherichia coli K-12. This compound did not produce any effect on the viability of dcm and dam dcm mutants. Furthermore, recA430 and lexA1 strains (both mutations interfere with LexA repressor cleavage but not recombination proficiency) were more resistant than the wild-type strain of E. coli K-12. In contrast, recBC and recA13 mutants were more sensitive to 5-azacytidine than the wild type. Transient exposure of E. coli to 5-azacytidine for 60 min induced both recA-dependent inhibition of cell division and induction of lambda prophage in Dcm+ strains but not in Dcm- mutants. Expression of both functions was dependent on recBC exonuclease. On the other hand, 5-azacytidine was unable to trigger the induction of umuCD and mucB genes and no amplification of RecA protein synthesis in either Dcm+ or Dcm- strains was observed. These last results are in agreement with previously reported data suggesting that there is a discrimination in the expression of the several SOS functions and that some SOS genes may be induced without amplification of RecA protein synthesis.

Adenosine Triphosphate↗