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L Escalante

Publications and source records attributed to L Escalante.

16 recordsLinked to original sources
PubMed1999

Phylogenetic analysis of Cryptosporidium parasites based on the small-subunit rRNA gene locus.

Biological data support the hypothesis that there are multiple species in the genus Cryptosporidium, but a recent analysis of the available genetic data suggested that there is insufficient evidence for species differentiation. In order to resolve the controversy in the taxonomy of this parasite genus, we characterized the small-subunit rRNA genes of Cryptosporidium parvum, Cryptosporidium baileyi, Cryptosporidium muris, and Cryptosporidium serpentis and performed a phylogenetic analysis of the genus Cryptosporidium. Our study revealed that the genus Cryptosporidium contains the phylogenetically distinct species C. parvum, C. muris, C. baileyi, and C. serpentis, which is consistent with the biological characteristics and host specificity data. The Cryptosporidium species formed two clades, with C. parvum and C. baileyi belonging to one clade and C. muris and C. serpentis belonging to the other clade. Within C. parvum, human genotype isolates and guinea pig isolates (known as Cryptosporidium wrairi) each differed from bovine genotype isolates by the nucleotide sequence in four regions. A C. muris isolate from cattle was also different from parasites isolated from a rock hyrax and a Bactrian camel. Minor differences were also detected between C. serpentis isolates from snakes and lizards. Based on the genetic information, a species- and strain-specific PCR-restriction fragment length polymorphism diagnostic tool was developed.

Animals↗
PubMed1997

Short report: screening for Trypanosoma cruzi in the blood supply by the Red Cross blood bank in Quito, Ecuador.

The status of Chagas' disease in Ecuador is not clear. In response to reports suggesting the possibility of transfusion-associated transmission of Chagas' disease in the blood bank in Quito, the Ecuadorian Red Cross in collaboration with the Instituto Nacional de Higiene, Zona Norte and the Tropical Disease Institute of Ohio University implemented a pilot Chagas' disease screening of the donated blood in the Quito blood bank. The results of the screening showed a low incidence of seropositivity among the donors (0.01% in 1994, 0.04% in 1995, and 0.02% in 1996) to the Quito blood bank and a higher seropositivity in samples donated to smaller blood banks (0.4% in 1994, 0.28% in 1995, and 0.13% in 1996) located in areas considered endemic, as well as from at least two areas previously considered nonendemic for Chagas' disease. This report highlights the need for a comprehensive evaluation of the prevalence and distribution of Chagas' disease in Ecuador.

Animals↗
PubMed1995

Blood donors in a vector-free zone of Ecuador potentially infected with Trypanosoma cruzi.

Chagas' disease is a serious health problem for the population of South and Central America. Blood transfusion is the second most common way in which this disease is transmitted. Several studies have reported finding Trypanosoma cruzi-infected blood in blood banks in endemic areas. Serum samples were taken from the Red Cross blood bank in Quito, a nonendemic and vector free zone of Ecuador, in December 1992 and May 1993 and analyzed by enzyme-linked immunosorbent assay using crude epimastigote extract from the Brazil strain of T. cruzi. Of 162 samples examined in December 1992, 12.1%, 13.9%, and 74% were seropositive, indeterminate, and seronegative, respectively. Of 173 samples taken in May 1993, 6.2%, 17.9%, 75.9% were seropositive, indeterminate, and seronegative, respectively. Western blot analysis of these sera using sodium dodecyl sulfate-polyacrylamide gel electrophoresis with 7.5% gels separated T. cruzi epimastigote antigen proteins, and revealed a reaction with a 205-kD doublet antigen with most of the seropositive samples. These results indicate the necessity for long-term screening of blood bank donors to reduce the risk of transfusion transmission of the disease even in areas of endemic countries where the vector is not present.

Animals↗
PubMed1995

Gentamicin formation in Micromonospora purpurea: stimulatory effect of ammonium.

The effect of ammonium on the fermentative production of gentamicin in Micromonospora purpurea has been studied using a chemically defined medium. Ammonium chloride concentrations ranging from 20 to 150 mM resulted in a proportional stimulation of growth and antibiotic formation. The use of other ammonium salts exerted a similar effect. Among the products of ammonium assimilation, glutamate and glutamine were able to exert the stimulatory effect. In addition, both amino acids reproduced the stimulation in resting cell systems of this microorganism and this result was not modified by the presence of chloramphenicol, eliminating a possible inductive action as the cause of this effect. The use of a glutamine synthetase inhibitor prevented antibiotic formation. This inhibition was reverted only by glutamine, suggesting that this amino acid was responsible of ammonium stimulation. Glutamine stimulation seems to be due to its ability to produce 2-deoxystreptamine and glucosamine, intermediates of the gentamicin biosynthetic pathway.

Ammonium Chloride↗
PubMed1994

Physiological studies on gentamicin: phosphate repression of antibiotic formation.

The effect of inorganic phosphate on the fermentative production of gentamicin by Micromonospora purpurea has been studied using a chemically defined medium. Phosphate concentrations higher than 5.75 mM (1 g/liter-1) did not inhibit growth but specifically prevented antibiotic formation. Changes in the pH medium and carbon or nitrogen depletion were excluded as the cause of antibiotic underproduction. The use of a phosphate analogue, a protein synthesis inhibitor and the profiles of differential rate of antibiotic production suggested that phosphate itself transiently repressed gentamicin formation. Phosphate affected the formation of 2-deoxystreptamine from 2-deoxyinosose, a none phosphorylated substrate.

Arsenates↗
PubMed1992

Carbon catabolite regulation of gentamicin formation.

The effect of utilizable carbon sources on the production of gentamicin by Micromonospora purpurea has been studied. High D-glucose and D-xylose concentrations (40 mg/ml), exerted a strong and permanent negative action on antibiotic formation. On the other hand, similar concentrations of D-fructose, D-mannose, maltose and starch caused no effect. The glucose action is seen only if added during the logarithmic growth phase; moreover, the sugar needs to be metabolized to show its negative effect.

Carbohydrate Metabolism↗
PubMed1990

Tuberculous meningitis. Short course of chemotherapy.

In March 1986, we began a 6-month short course trial of therapy for tuberculous meningitis, in which 28 patients were analyzed. The diagnosis was based on the following cerebrospinal fluid test results: in 53.5% of the cases, Mycobacterium tuberculosis was identified by direct smear; in 57%, culture in Löwenstein-Jensen medium was positive; in 83.3%, the detection of anti-bacille Calmette-Guérin (BCG) antibodies by enzyme-linked immunosorbent assay was positive; and in 74%, the dosification of adenosine deaminase activity was positive. In addition, in 21.4% of the cases, the diagnosis was established by means of autopsy findings. Moreover, the diagnosis was supported by bacteriological analyses from another tissue or body fluids. Despite the administration of an antituberculous therapy, 32.4% of the patients died: all of the decreased had reached the last stage of the disease by the beginning of treatment. Sixteen percent of the patients who survived after more than 18 months of follow-up after therapy had ended suffered neurological sequelae. With the 6-month therapeutic regimen, the morbidity/mortality is similar to that found in the longer-course therapies. The latter regimen is therefore thought to be a good and acceptable therapeutic option for the treatment of tuberculous meningitis.

Adolescent↗
PubMed1989

Neurocysticercosis. Short course of treatment with albendazole.

Eighteen patients with nonenhancing parenchymal brain cysts were treated with albendazole; 9 patients were treated for 3 days and 9 patients for 1 month at daily doses of 15 mg/kg of body weight. Three months after starting therapy, results showed that in both groups the treatment was highly effective. Control studies carried out in the same group before the trial did not show any significant improvement. Five patients were controls and were treated only with symptomatic drugs. The total diameter of the lesions was reduced from 220.1 mm to 52.1 mm, which signifies a reduction of 76.3% in patients treated for a period of 3 days, and from 278.5 mm to 82.1 mm, which is 70.5%, in patients treated for 30 days. We conclude that albendazole administered according to the 3-day therapeutic scheme proposed above is as highly effective for the treatment of parenchymal brain cysticercosis as the 30-day scheme.

Adolescent↗
PubMed1988

Glutathione formation in Penicillium chrysogenum: stimulatory effect of ammonium.

Penicillium chrysogenum produced glutathione after growth in a defined medium containing 10 mM-NH4Cl as the sole source of nitrogen. The use of higher ammonium concentrations (100 mM) resulted in stimulation of growth and glutathione formation. In addition, increases in the intracellular pools of glutamate, alanine and glutamine, proportional to the amount of ammonium present in the medium were observed. Resting cell systems, prepared from cells previously grown with ammonium, were able to produce glutathione when incubated with ammonium or the amino acids glutamate, alanine and glutamine. A mutant lacking NADP-dependent glutamate dehydrogenase activity (which has a leaky phenotype on ammonium as sole nitrogen source) required glutamate to synthesize glutathione. Resting cell systems of this mutant, prepared from cells previously grown with ammonium, did not produce glutathione even when incubated with glutamate or glutamine. On the other hand, resting cell systems of this mutant produced glutathione if prepared from cells previously grown with glutamate. The addition of glutamate to resting cell systems of the wild-type strain stimulated the synthesis of gamma-glutamylcysteine synthetase, the first enzyme of glutathione biosynthesis.

Ammonium Chloride↗
PubMed1982

Transient repression of erythromycin formation in Streptomyces erythraeus.

The effect of a D-glucose on growth and erythromycin production by Streptomyces erythraeus was investigated. D-Glucose stimulated growth and caused a strong but temporary suppression of antibiotic formation. Maximum specific suppression of erythromycin formation occurred at a carbohydrate concentration of 20 mg ml-1. A non-metabolizable analogue of glucose, 2-deoxy-D-glucose, also suppressed antibiotic formation. Since glucose caused a decrease in erythromycin formation only when added before the stage of antibiotic production, we conclude that this sugar exerted a transient repressive effect on erythromycin biosynthesis.

Deoxyglucose↗
PubMed1980

Characterization of a site-specific restriction endonuclease SphI from Streptomyces phaeochromogenes.

A new type-II restriction endonuclease SphI, has been partially purified from Streptomyces phaeochromogenes. SphI recognizes the hexanucleotide sequence 5'-GCATGC and cleaves it at the position marked by the arrow. This nucleotide sequence is present twice in SV40 DNA, four times lambda DNA and only once in the cloning vehicles pBR322, pBR325, pBR327 and pBR328.

Chromatography, DEAE-Cellulose↗
PubMedDate not supplied

Prevalence of anti-Taenia solium antibodies in sera from outpatients in an Andean region of Ecuador.

Sera from 9,254 individuals that presented at one of three outpatient clinics in Quito, Ecuador were assayed by indirect hemagglutination for the presence of antibodies reactive with antigens from Taenia solium cysts. Immunoblot analysis of 81 selected sera with IHA titers ranging from 0 to 1,028 showed that a titer of > or = 32 was suggestive of exposure to the parasite. Nine percent (9%) of the 9,254 patients had titers of 32 or greater. Of 3,503 sera from one clinic, which included sera from food handlers undergoing yearly physicals, 390 (11%) were positive. In addition, a correlation with age was seen in some, but not all, populations. In situations where age-related effects were noted, the highest incidence was seen in the youngest (0-20 years) and in the oldest (51-60 years) group. Thus, a resurgence of infection after a period of lower prevalence may be developing. Overall, this study shows that cysticercosis is relatively common and potentially a serious health problem in this region.

Adolescent↗
PubMedDate not supplied

Differentiating human from animal isolates of Cryptosporidium parvum.

We analyzed 92 Cryptosporidium parvum isolates from humans and animals by a polymerase chain reaction/restriction fragment length polymorphism method based on the thrombospondin-related anonymous protein 2 gene sequence. Used as a molecular marker, this method can differentiate between the two genotypes of C. parvum and elucidate the transmission of infection to humans.

Animals↗