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A Contreras

Publications and source records attributed to A Contreras.

At least 73 records · Page 4Linked to original sources
PubMed1996

Smoking history-taking skills: a simple guide to teach medical students.

Many doctors rate themselves as ineffective smoking cessation counsellors. It is logical to initiate training efforts with medical students. We incorporated smoking history-taking in the physical diagnosis course at the University of North Carolina at Chapel Hill using a simple method to teach smoking history-taking skills and to assess its effectiveness as an educational intervention. The principal intervention was the distribution of a one-sheet Smoking-History Taking and Counseling Guide, adapted from the American Lung Association's Freedom From Smoking for You and Your Family self-help manual. The second intervention was a single prompt for 50% of the course preceptors. Students' smoking history-taking skills were evaluated in the Objective Structured Clinical Examination (OSCE) at the end of the course. Students who received the guide did significantly better on the OSCE, even after controlling for having discussed taking a smoking history with their preceptors. A simple guide combined with a one-time prompting of preceptors has a positive effect on the acquisition of smoking history-taking skills by the medical students. This strategy may also be useful for teaching and evaluating smoking-cessation counselling skills, for which good smoking history-taking is a necessary basis.

Clinical Competence↗
PubMed1996

Mammalian viruses in human periodontitis.

A prior investigation has demonstrated a higher prevalence of human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) in subgingival specimens from periodontitis patients than from gingivitis patients. This study aimed to determine the frequency of HCMV, EBV-1, EBV-2, herpes simplex virus (HSV) and human immunodeficiency virus (HIV) in subgingival samples from 27 adults who each contributed both a periodontitis and a gingivitis site. Viral detection was performed using a nested-polymerase chain reaction method. Twenty-four subjects (89%) yielded at least one of the five test viruses from deep periodontal pockets, whereas only 15 (56%) showed viruses from shallow periodontal sites (P = 0.015; chi-square test). Viral co-infection occurred more frequently in deep than in shallow periodontal sites (P = 0.015). HCMV was detected with higher frequency in deep than in shallow periodontal sites (P = 0.023). The possible periodontopathogenic mechanisms of mammalian viruses in human periodontitis are discussed. The role and importance of HCMV and other mammalian viruses in the initiation and progression of destructive periodontal disease merits further investigation.

Adult↗
PubMed1994

[Evaluation of the Reinforced subprogram of the Chilean National supplemental Nutrition Program].

Chile's National Supplementary Feeding Program constitutes the main food intervention program of the country. Its annual budget amounts to US $ 65 million covering approximately 55% of the national population of children under 6 years of age. It includes two subprograms, the Basic one for normally growing children and the Reinforced one for undernourished children and those at risk of becoming undernourished. This last group amounted in 1990 to 17% of the total, receiving 50% of the food distributed. This study is the first evaluation carried out on the Reinforced subprogram, having as general objective to measure its efficiency in terms of the change in the nutritional status of the targeted children. Presently, children under two are targeted if a) are undernourished by wt/ht (< -1 S.D. NCHS) or b) have less weight increase than 75% of the Ministry of Health's norm (similar to NCHS) during two consecutive health controls. The only way these children are discharged is, if during three consecutive controls (monthly) they increase more than 75% of the same norm. The analysis involved nutritional evaluations at birth, when the children were targeted and when they were discharged, showing that the improvement of their nutritional status was very unsatisfactory.

Animals↗
PubMed1993

Transmissible gastroenteritis in pigs in south east Spain: prevalence and factors associated with infection.

In the Murcia region of south east Spain, epidemics of transmissible gastroenteritis-like disease have occurred in pigs every three years since 1980. In 1987 a sero-epidemiological survey was conducted to estimate the prevalence and spread of transmissible gastroenteritis virus (TGEV) infection among breeding pigs and farms, and to determine any association between the infection and herd size and geographical zone. The Murcia region was divided into four geographical zones and the farms were classified by size into four categories. The random sample was statistically representative of both the breeding stock and the farms in each geographical zone, and the analyses involved 6000 breeding pigs from 480 farms. The immunological techniques employed were the indirect ELISA and the blocking ELISA. The prevalence of seropositive breeding pigs was 1.27 +/- 0.28 per cent and the prevalence of infected farms was 5 +/- 1.94 per cent. On the infected farms, the prevalence of seropositive pigs ranged from 5 to 60 per cent. The infection occurred throughout the Murcia region, but a significant association (P < 0.01) was observed between the geographical zone and the prevalence of TGEV infection. Herds with > or = 50 breeding pigs had a greater prevalence (P < 0.01) of TGEV infection.

Animals↗
PubMed1993

[Hemolysis induced by Loxosceles laeta venom. In vitro experience].

To study the effects of loxosceles laeta venom on red blood cells and the possible factors involved in hemolysis during arachnidism, in vitro models were designed to measure the role of loxosceles venom, calcium, complement and antibodies in the mechanism of red blood cell destruction. The degree of basal hemolysis was measured in a 5% suspension of group O, Rh (+) red blood cells in pH 7.4 buffer. In a similar suspension spider venom was added in amounts equivalent to one venom gland. After 72 hours of incubation, basal hemolysis was 5.59 +/- 2.04% which increased to 26.01 +/- 7.9% adding venom (p < 0.001). Adding calcium to the incubation medium, hemolysis increased to 88.5 +/- 7.16% (p < 0.001). Incubating red blood cells with control human serum and venom, hemolysis was 14.58 +/- 2.42%, which decreased significantly to 6.85 +/- 3.35% when serum was heat inactivated; this demonstrates an effect of the presence of complement. We did not find antivenom antibody production in patients with arachnidism 10, 15 or 30 days after the spider bite. It is thus demonstrated that loxosceles laeta venom has a direct lytic action on red blood cells that is calcium and complement dependent and is not mediated by antibodies or other substance.

Animals↗
PubMed1993

Comparative study of different immunoserological techniques for the detection of antibodies against transmissible gastroenteritis (TGE) coronavirus.

In order to carry out a sero-epidemiological survey of transmissible gastroenteritis (TGE) infection in a high-density pig-breeding area the Murcia region, Spain), the sensitivity and the specificity of 5 different techniques were compared. Twenty-four sera from non-infected and infected pigs were analyzed by the following tests: in vitro neutralization, indirect ELISA with concentrated virus, indirect ELISA with purified virus, immunocapture ELISA and VELCIA (virus-enzyme linked cell immunoassay). All sera from infected pigs were detected as positive only by seroneutralization, ELISA with purified virus and VELCIA (sensitivity 100%). False-positive sera were detected with several tests (ELISA with purified virus and concentrated virus, ELISA immunocapture with a specificity of 88, 88 and 76% respectively). Only VELCIA provided a specificity as high as that obtained with seroneutralization (100%).

Animals↗
PubMed1992

Pathogenicity and antigen detection of the Nouzilly strain of transmissible gastroenteritis coronavirus, in 1-week-old piglets.

We compared the pathogenicity and the sites of multiplication of the attenuated Nouzilly strain, with the highly passaged Purdue-115 and the virulent Gep II strains of transmissible gastroenteritis (TGE) coronavirus, in 1-week-old weaned piglets. The immunohistochemical peroxidase technique, with an antiviral nucleoprotein monoclonal antibody, was used for the localization of the multiplication sites, in the intestine and other organs. The Gep II and the Purdue-115 strains, administered orally to piglets, caused clinical signs and lesions of TGE. These strains multiplied within the intestinal tract in the enterocytes of the jejunum and ileum, Peyer's patches and mesenteric lymph nodes. In view of the small numbers of infected cells in the tonsils, spleen, kidney, liver and lung, these tissues are not considered to be preferential multiplication sites. The attenuated Nouzilly strain multiplies only in the ileum and the mesenteric lymph nodes. The variation in the tropism for particular parts of the intestine (with the preferential localization of the virus in the ileum rather than the jejunum), could be related to the high degree of attenuation of the Nouzilly strain.

Animals↗
PubMed1992

gyrB mutations which confer coumarin resistance also affect DNA supercoiling and ATP hydrolysis by Escherichia coli DNA gyrase.

Coumarins are inhibitors of the ATP hydrolysis and DNA supercoiling reactions catalysed by DNA gyrase. Their target is the B subunit of gyrase (GyrB), encoded by the gyrB gene. The exact mode and site of action of the drugs is unknown. We have identified four mutations conferring coumarin resistance to Escherichia coli: Arg-136 to Cys, His or Ser and Gly-164 to Val. In vitro, the ATPase and supercoiling activities of the mutant GyrB proteins are reduced relative to the wild-type enzyme and show resistance to the coumarin antibiotics. Significant differences in the susceptibility of mutant GyrB proteins to inhibition by either chlorobiocin and novobiocin or coumermycin have been found, suggesting wider contacts between coumermycin and GyrB. We discuss the significance of Arg-136 and Gly-164 in relation to the notion that coumarin drugs act as competitive inhibitors of the ATPase reaction.

Adenosine Triphosphate↗
PubMed1992

Sero-epidemiological survey of porcine respiratory coronavirus (PRCV) infection in breeding herds in southeastern Spain.

In 1987 we conducted a sero-epidemiological survey in the Murcia Region (South-East Spain) to discover the prevalence and spread of PRCV-infection among breeding pigs and farms and determine the association between herd size and geographical zone with PRCV-infection. The Murcia Region was divided into four geographical zones and the farms classified by size in four categories. The random sample was statistically representative of both the breeding stock and farms in each geographical zone. We analysed 6,000 breeding pigs from 480 farms. The immunological techniques employed were indirect ELISA and blocking ELISA. The prevalence (P +/- IC) of PRCV-seropositive breeding pigs and infected breeding farms was 14.53 +/- 0.89% and 21.87 +/- 7.83% respectively. On 55% of the infected farms, the prevalence of seropositive breeding pigs was 60-100%. PRCV-infection appears spread throughout the four geographical zones of the Murcia Region. However, a significant association (p less than 0.01) was observed between geographical zone and the prevalence of PRCV-infection. A herd size of greater than 50 breeding pigs had a greater risk (p less than 0.01) of PRCV-infection.

Animals↗
PubMed1991

Cys184 and Cys187 of NifL protein of Klebsiella pneumoniae are not absolutely required for inhibition of NifA activity.

The sequence Cys184-Ala-Asp-Cys187 in the NifL protein of Klebsiella pneumoniae, for which a role in oxygen sensing and/or metal binding has been proposed, was altered by introducing two mutations, Cys184----Ala and Cys187----Ala, using oligodeoxyribonucleotide-directed mutagenesis. Neither mutation abolished ammonium or oxygen control of nif transcription, although some impairment of function was apparent. The two Cys residues are therefore unlikely to have a direct role in oxygen sensing or metal binding, but probably make some contribution to protein folding or stability.

Amino Acid Sequence↗
PubMed1991

Tn5 mutagenesis and insertion replacement in Azotobacter vinelandii.

Tn5 insertion mutants of Azotobacter vinelandii were isolated using vectors pJB4JI (IncP) and pGS9 (IncN). A procedure to replace Tn5 (Kmr) by its nontransposing derivative Tn5-131 (Tcr) was developed. For the replacement, a ColEl derivative harboring Tn5-131 (pRZ131) was conjugally mobilized by the IncN plasmid pCU101 into A. vinelandii strains containing Tn5. Both plasmids are unable to be maintained in A. vinelandii, but the transient presence of pRZ131 allows recombination between the incoming and the resident Tn5 elements. Genetic and physical analysis showed that insertion replacements result in lower frequencies of Tn5-associated genomic rearrangements, thereby increasing the stability of Tn5-containing strains.

Azotobacter↗
PubMed1991

Conditional-suicide containment system for bacteria which mineralize aromatics.

A model conditional-suicide system to control genetically engineered microorganisms able to degrade substituted benzoates is reported. The system is based on two elements. One element consists of a fusion between the promoter of the Pseudomonas putida TOL plasmid-encoded meta-cleavage pathway operon (P(m)) and the lacI gene encoding Lac repressor plus xylS, coding for the positive regulator of P(m). The other element carries a fusion between the P(tac) promoter and the gef gene, which encodes a killing function. In the presence of XylS effectors, LacI protein is synthesized, preventing the expression of the killing function. In the absence of effectors, expression of the P(tac)::gef cassette is no longer prevented and a high rate of cell killing is observed. The substitution of XylS for XylSthr45, a mutant regulator with altered effector specificity and increased affinity for benzoates, allows the control of populations able to degrade a wider range of benzoates at micromolar substrate concentrations. Given the wide effector specificity of the key regulators, the wild-type and mutant XylS proteins, the system should allow the control of populations able to metabolize benzoate; methyl-, dimethyl-, chloro-, dichloro-, ethyl-, and methoxybenzoates; salicylate; and methyl- and chlorosalicylates. A small population of genetically engineered microorganisms became Gef resistant; however, the mechanism of such survival remains unknown.

Journal Article↗
PubMed1991

The product of the nitrogen fixation regulatory gene nfrX of Azotobacter vinelandii is functionally and structurally homologous to the uridylyltransferase encoded by glnD in enteric bacteria.

We sequenced the nitrogen fixation regulatory gene nfrX from Azotobacter vinelandii, mutations in which cause a Nif- phenotype, and found that it encodes a 105-kDa protein (NfrX), the N terminus of which is highly homologous to that of the uridylyltransferase-uridylyl-removing enzyme encoded by glnD in Escherichia coli. In vivo complementation experiments demonstrate that the glnD and nfrX products are functionally interchangeable. A vinelandii nfrX thus appears to encode a uridylyltransferase-uridylyl-removing enzyme, and in this paper we report the first sequence of such a protein. The Nif- phenotype of nfrX mutants can be suppressed by a second mutation in a recently identified nifL-like gene immediately upstream of nifA in A. vinelandii. NifL mediates nif regulation in response to the N status in A. vinelandii, presumably by inhibiting NifA activator function as occurs in Klebsiella pneumoniae; thus, one role of NfrX is to modify, either directly or indirectly, the activity of the nifL product.

Adenine↗
PubMed1991

[Prototype of an instrument for retrograde obturation].

Several instruments to carry and put the silver amalgam into de apical foramen for it's posterior condensation without spreading this material over the periodontal tissues, bone and adyacent mucosa, has been designed along the years. This article describes an easier and cheaper way to make an endodontic amalgam carrier by the adaptation between en 18 and 22 mm intravenous catheters into disposable syringes by the use of autopolymerizable acrilic, given the dentist the option of making a very easy instrument, at a low cost which can be used as a commercial endodontic amalgam carrier as well.

Acrylic Resins↗
PubMed1990

The function of isolated domains and chimaeric proteins constructed from the transcriptional activators NifA and NtrC of Klebsiella pneumoniae.

A model for the domain structure of sigma 54-dependent transcriptional activators, based on sequence data, has been tested by examining the function of truncated and chimaeric proteins. Removal of the N-terminal domain of NtrC abolishes transcriptional activation, indicating that this domain is positively required for activator function. Over-expression of this domain as a separate peptide appears to titrate out the phosphorylating activity of NtrB. Removal of the N-terminal domain of NifA reduces activation 3-4-fold. The residual activity is particularly sensitive to inhibition by NifL, suggesting that the role of the N-terminal domain is to block the action of NifL in derepressing conditions. The C-terminal domain of NtrC showed repressor activity when expressed as a separate peptide. This domain is necessary for activator function even when NtrC binding sites are deleted from promoters. A point mutation in the ATP-binding motif of the NtrC central domain, Ser169 to Ala, also abolished activator function. Exchanging the N-terminal domains of Klebsiella pneumoniae NtrC, NifA and Escherichia coli OmpR, did not produce any hybrid activity, suggesting that N-terminal domains in the native proteins specifically recognize the rest of the molecule.

Bacterial Proteins↗
PubMed1988

The effect on the function of the transcriptional activator NtrC from Klebsiella pneumoniae of mutations in the DNA-recognition helix.

We have constructed mutations in what we predict to be the DNA-recognition helix of Klebsiella pneumoniae NtrC, which regulates transcription from promoters under global nitrogen control. Mutations which disrupt the helix lead to complete loss of function. All point mutants tested were able to activate transcription from the sigma 54-dependent glnA promoter, but only those retaining some ability to recognise NtrC binding sites, as evidenced by their ability to repress the ntrB promoter and the upstream glnA promoter, were able to activate the nifL promoter. One mutant, which contained an amino acid substitution in the turn of the DNA-binding motif as well as in the recognition helix, suppressed mutations in the NtrC binding sites upstream from the nifL promoter, but only if both sites bore equivalent transitions. This confirms that the DNA-binding motif for this class of transcriptional activator has been correctly identified and suggests that binding of NtrC can be cooperative.

Amino Acid Sequence↗
PubMed1987

Tn10 mutagenesis in Azotobacter vinelandii.

The tetracycline-resistant transposon Tn10 and its "high-hopper" derivative Tn10HH104 were introduced into the Azotobacter vinelandii genome using suicide conjugative plasmids derived from pRK2013. Several types of mutants induced by either of these elements are described. Nif- mutants (deficient in nitrogen fixation) were easily isolated, whereas the isolation of other mutant types (auxotrophs, sugar non-users) required special selection conditions. The characterization of the mutations as transposon insertions was often complicated and sometimes required a combination of genetic and physical tests. A common source of complication, the existence of double inserts, was found among the mutants induced by Tn10HH104 but not among those induced by Tn10. Both the high-hopper and the wild-type element proved to undergo secondary transpositions, albeit at different frequencies. Another type of complication, the existence of heterozygotes, occurred because of the high level of redundancy of the A. vinelandii genome.

Azotobacter vinelandii↗