PubMed Health⌕ Search

Biomedical subjects

A Cravioto

Publications and source records attributed to A Cravioto.

At least 37 records · Page 2Linked to original sources
PubMed1997

Coli surface antigens associated with enterotoxigenic Escherichia coli strains isolated from persons with traveler's diarrhea in Asia.

Enterotoxigenic Escherichia coli (ETEC) strains were isolated from travelers or military personnel who developed diarrhea after visiting Nepal or who were deployed to Thailand, Indonesia, or the Philippines. ETEC isolates were examined for colonization factor antigen (CFA). CFAs were identified on 59% (40 of 68) of the isolates examined. The lack of a detectable CFA on 41% (28 of 68) of the isolates is of concern for the development of an effective ETEC vaccine.

Antigens, Bacterial↗
PubMed1996

Enteroaggregative Escherichia coli heat-stable enterotoxin is not restricted to enteroaggregative E. coli.

Enteroaggregative Escherichia coli (EAggEC) have been implicated as diarrheal pathogens in several settings. Some EAggEC produce a distinct heat-stable enterotoxin named EAST1. The distribution and prevalence of the EAST1 gene in selected groups of bacterial enteropathogens were determined by colony hybridization. One hundred percent of 75 O157:H7 enterohemorrhagic E. coli (EHEC), 41% of 227 EAggEC, 41% of 149 enterotoxigenic E. coli, 22% of 65 enteropathogenic E. coli (EPEC), and 38% of 47 E. coli stool isolates from asymptomatic children hybridized with an EAST1 DNA probe. None of 55 enteroinvasive E. coli, 12 Yersinia enterocolitica, or 20 Vibrio cholerae non-O1 strains were EAST1 probe-positive. Concordance between EAST1 genotype and enterotoxicity was shown in examined strains of EAggEC, EHEC, and EPEC. The gene encoding EAST1 is more broadly distributed among diarrheogenic E. coli than previously known and may represent an additional determinant in the pathogenesis of E. coli diarrhea.

Bacterial Adhesion↗
PubMed1995

Heterogeneity of enteroaggregative Escherichia coli virulence demonstrated in volunteers.

Enteroaggregative Escherichia coli (EAggEC) are diarrheal pathogens defined by aggregative adherence to HEp-2 cells. In an effort to identify pathogenic EAggEC isolates, four groups of 5 volunteers were fed 1 of 4 different EAggEC strains, each at a dose of 10(10) cfu. Strain 042 caused diarrhea in 3 of 5 adults; 3 other EAggEC isolates (17-2, 34b, and JM221) failed to elicit diarrhea. A gene encoding enterotoxin EAST1 was found in strains 042 and 17-2 but not 34b or JM221; a 108-kDa cytotoxin was expressed in all 4 isolates. All 4 isolates showed a modest degree of gentamicin protection in HEp-2 cells. 17-2, 34b, and JM221 expressed the fimbrial antigen AAF/I; 042 did not express this fimbria as determined by immunogold electron microscopy and genetic probe hybridization.

Bacterial Adhesion↗
PubMed1994

Immunoglobulin A antibodies directed against Campylobacter jejuni flagellin present in breast-milk.

We studied the relationship between IgA anti-campylobacter flagellin antibodies in breast milk samples and protection of breastfed infants living in a rural Mexican village from campylobacter infection. There were fewer episodes of campylobacter infection (symptomatic and asymptomatic combined) in infants breastfed with milk containing specific anti-flagellin antibodies (1.2/child/year, 95% CI 0.6-1.8) versus non-breastfed children (3.3/child/year, 95% CI 1.8-4.8; P < 0.01). Infants breastfed with milk that was anti-flagellin antibody negative by ELISA also had fewer episodes of infection compared with non-breastfed children, but the difference did not reach statistical significance (1.8/child/year, 95% CI 0.7-3.0 versus 3.3/child/year, 95% CI 1.8-4.8, P > 0.05). Breastfeeding has a protective effect against campylobacter infection and is associated with the presence of specific antibodies directed against campylobacter flagellin.

Analysis of Variance↗
PubMed1994

Isolates of Escherichia coli O44:H18 of diverse origin are enteroaggregative.

One hundred thirteen strains of Escherichia coli O44:H18 isolated in several countries over 25 years were examined for adhesion to tissue culture cells and for hybridization with DNA probes. Fifty-nine strains were from sporadic cases of infection; 54 were from 12 outbreaks. Of the 113 strains, 85 showed aggregative adhesion to HEp-2 cells; 36 were from sporadic cases and 49 were from 9 outbreaks. All adhesive strains hybridized with the probe for enteroaggregative E. coli (EAggEC) and 1 nonadhesive strain was also positive. However, 80 of the 86 EAggEC probe-positive strains also hybridized with the probe for diffusely adherent E. coli (DAEC) derived from the daaC gene of strain F1845. The EAggEC and DAEC probes hybridized to different fragments of a large plasmid in the O44:H18 strains.

Aged↗
PubMed1993

Rotavirus-inhibitory activity in serial milk samples from Mexican women and rotavirus infections in their children during their first year of life.

A total of 75 children born in rural Mexico were followed for diarrheal diseases and rotavirus (RV) excretion during the first year of life. For 18 children, an average of 14 serial breast milk samples were obtained between days 2 and 360 after delivery and were tested for RV-inhibitory activity. Of these samples, 70, 62, and 85% showed inhibitory activity against serotype (ST) 1 human RV, ST4 human RV, and ST3 simian RV, respectively; the median titers were 10, 10, and 20, respectively. Some 89% of the milk samples showed RV-specific antibodies in an enzyme-linked immunosorbent assay (median titer, 20). Surprisingly, 98% of the milk samples inhibited ST6 bovine RV. ST6, but not ST1, RV-inhibitory activity survived heat treatment (10 min at 80 degrees C). Of the 18 children tested, 13 children experienced 23 episodes of diarrhea (enterotoxigenic [n = 8] and enteropathogenic [n = 3] Escherichia coli, Campylobacter jejuni [n = 4], Shigella flexneri [n = 2], RV [n = 1]) and 5 children experienced 6 RV infections. Only one RV infection was associated with diarrhea. The five RV excretors did not differ from the nonexcretors with respect to the RV-inhibitory activity in the breast milk fed to them. The RV-inhibitory titers were too low in the majority of the studied Mexican milk samples to indicate an important effect of breast-feeding on the take rate of oral human, simian, or reassortant RV vaccines. Breast-feeding might, however, inhibit the take rate of a bovine RV vaccine.

Adult↗
PubMed1992

Biological characterization of the naturally occurring analogues of intrapituitary human follicle-stimulating hormone.

In the present studies we analysed the main physicochemical and biological properties of the several isoforms of human pituitary follicle-stimulating hormone (hFSH). Extracts of total anterior pituitary glycoproteins from adult donors were submitted to chromatofocusing and several forms of immunoactive hFSH with isoelectric points (pI) ranging from 7.6 to 3.8 were identified. An additional isoform was detected after passing through the chromatofocusing column a 1.0 M NaCl solution (salt peak). Each hFSH isoform or pool of neighbouring isoforms (pI value 7.6-7.1, pool I, 1.5 +/- 0.13% of total immunoactivity recovered; pI value 5.9-5.3, pool II, 8.9 +/- 1.6% of total; pI value 5.0-4.7, pool III, 14.4 +/- 1.4% of total; pI value 4.5-4.1, pool IV, 54.8 +/- 4.9% of total; pI value 3.9-3.8, pool V, 3.67 +/- 0.9% of total; salt peak, pool VI, 16.8 +/- 4.8% of total) eluted as single hFSH peaks after Sephadex G-100 exclusion chromatography (apparent Mr 60,000). Even though hFSH present within each pool was recognized by a receptor preparation, the receptor-binding activity expressed as the radioreceptor assay:radioimmunoassay (RRA/RIA) activity ratio varied with the pI value of the particular hFSH isoform tested; starting from a pI value of 5.9, the receptor-binding activity of hFSH decreased from 4.25 +/- 0.28 to 1.17 +/- 0.14, as the pI value of the corresponding isoform declined. A similar trend was observed when the potency of each isoform was assessed by an in vitro bioassay.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of gonadotrophin-releasing hormone, recombinant human activin-A and sex steroid hormones upon the follicle-stimulating isohormones secreted by rat anterior pituitary cells in culture.

FSH is produced and secreted from the anterior pituitary gland of rats in multiple molecular forms. At times of high gonadotrophin-releasing hormone (GnRH) and oestrogen output (e.g. the morning of the day of pro-oestrus) the pituitary increases the production of FSH isoforms with isoelectric point (pI) values greater than 5.0, whilst sex steroid deprivation leads to the production of strongly acidic and less in-vitro biologically active FSH molecules. It is not known, however, whether sex steroids modulate the production of specific FSH isoforms by a direct action at the pituitary level or indirectly through altering the rate of synthesis and/or secretion of GnRH. In order to obtain some insight on this issue, we examined the charge heterogeneity of FSH secreted by cultured pituitary cells exposed to different FSH-releasing factors, oestradiol-17 beta and progesterone, alone or in different time-sequenced combinations. Anterior pituitary glands from 21-day-old female rats were enzymatically dispersed into a single cell suspension and cultured for 5 days. During days 1 to 3, cells were incubated in the absence of factors or steroid hormones; on days 3 to 4, cells were incubated in the absence (controls) or presence of either oestradiol-17 beta (3.67 nmol/l) or oestradiol-17 beta plus progesterone (3.67 and 31.8 nmol/l respectively). Finally, during days 4 to 6, GnRH (10 nmol/l) or recombinant human activin-A (2 nmol/l) were added to half of all culture wells. Media from each cell group were concentrated and the several forms of secreted FSH were then separated by polyacrylamide gel isoelectric focusing (pH range 6.5-4.0) and quantitated. All media concentrates contained several forms of immunoactive secreted FSH focusing within a pH range of 6.44-4.23. A large amount (51-76%) of total FSH recovered focused within a pI range of 4.9-4.0 (area 3), whilst 20-43% and 4-8% of the total were identified within pI range of 5.9-5.0 (area 2) and 6.5-6.0 (area 1) respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Activins↗
PubMed1991

Association of Escherichia coli HEp-2 adherence patterns with type and duration of diarrhoea.

373 (59%) out of 636 faecal specimens obtained during the first 2 years of life of 72 Mexican children yielded adherent Escherichia coli (HEp-2 cells). Strains with localised adherence were significantly associated with acute non-bloody diarrhoea, whereas strains with aggregative adherence were significantly associated with persistent diarrhoea. Half the strains with localised adherence were not enteropathogenic E coli serotypes nor did they hybridise with an enteropathogenic E coli adherence factor DNA probe. All strains with localised adherence gave a positive fluorescent actin staining (FAS) assay, irrespective of serotype. One-third of children colonised by aggregative strains had bloody diarrhoea. Isolation of strains with diffuse adherence was not related to type or duration of diarrhoea but was generally associated with isolation of another pathogenic organism.

Acute Disease↗
PubMed1991

Inhibition of localized adhesion of enteropathogenic Escherichia coli to HEp-2 cells by immunoglobulin and oligosaccharide fractions of human colostrum and breast milk.

Secretory IgA (sIgA) purified from colostrum and breast milk obtained from 14 women inhibited the localized adherence of an enteropathogenic Escherichia coli (EPEC) to HEp-2 cells. Inhibition decreased as lactation continued even when the concentration of sIgA was maintained constant at 1 mg/ml. sIgA responded to a 94-kDa plasmid-encoded outer membrane protein implicated as the EPEC adherence factor. An oligosaccharide-enriched fraction (OEF) from these samples also inhibited the attachment of this EPEC. Inhibition by OEFs decreased as lactation continued because of a general reduction in oligosaccharide content. Localized adherence of six other EPEC was also inhibited by sIgA and OEF, whereas attachment of isolates with diffuse or aggregative adherence was not inhibited by these fractions. Experiments with purified oligosaccharide fractions revealed that EPEC attach to HEp-2 cells through a carbohydrate-mediated mechanism based on the preferential recognition of fucosylated residues in human milk.

Bacterial Adhesion↗
PubMed1991

[Patterns in the household acceptance of oral rehydration therapy in a cohort of rural mothers].

The household acceptance of oral rehydration solution salts was studied in a cohort of 75 rural mothers over a two year period. The study was carried out in a rural Mexican village between August 1985 and February 1988. There were 636 episodes of diarrhea, with an average of four episodes per child per year. There were no deaths due to diarrhea or its complications and only 2% of these episodes required the use of parenteral solutions. Acceptance of oral rehydration remained around 50% during subsequent bouts of diarrhea. Variables such as a medium high socioeconomic level of the family, and the reading of journals and newspapers by the mother and the presence of water supply in the home were significantly associated with the acceptance of oral rehydration treatment. On the other hand, families classified as traditional rejected the procedure with significantly higher frequency. The data presented indicates the need for redesigning oral rehydration, treatment programs to increase their impact at the community level.

Adult↗
PubMed1991

[A comparative study between the use of the Spicer-Edwards method and the coagglutination reaction for identifying Salmonella antigens].

A comparative study between tube agglutination using Spicer-Edwards antisera and a coagglutination method using Staphylococcus aureus Cowan 1 (NCTC 8530) protein A to detect Salmonella flagellar antigens was carried out. A total of 39 Salmonella strains belonging to eight serogroups of the Kauffmann-White scheme were typed by both methods. Each serogroup include monophasic and biphasic strains. Statistical analysis of the results showed that the coagglutination method was more sensitive and specific that the classic tube agglutination method normally used in different laboratories. The use of less antiserum in the coagglutination method to detect Salmonella antigens without loss of specificity or sensitivity represents an important saving for clinical laboratories and for epidemiologic research that require the identification of these antigens.

Agglutination Tests↗
PubMed1991

[Campylobacter jejuni infection in children of a rural community].

Colonization of the intestine with Campylobacter jejuni was followed longitudinally from birth in a cohort of 75 rural children with fecal cultures taken every fortnight and every time they had diarrhea. Only 25% of children initially colonized with C. jejuni during the first year of life, and 12% of children initially colonized during the second had diarrhea. The age at which a child was initially infected with C. jejuni was not a risk factor in relation with presence of disease. A higher illness-to-infection ratio (P less than 0.05) was found during subsequent colonization with C. jejuni when initial infection was associated with diarrhea. Risk of diarrhea during initial or subsequent colonization with C. jejuni was not related with the production of cholera-like enterotoxin, a cytotoxic active on HeLa cells or with adhesive ability to HEp-2 cells by the infecting strains.

Campylobacter Infections↗
PubMed1991

[Etiology of bloody diarrhea in children from a rural community].

The etiology of bloody diarrhea was investigated in a cohort of 75 children followed longitudinally from birth during the first two years of life in a rural Village of Central Mexico. Of a total of 636 episodes of diarrhea, 71 (11%) showed presence of blood. A single associated pathogen was isolated in 59 (83%) of 71 children; 35% showed the presence of enteroaggregative E. coli (EAEC), 11% of E. coli producing Shiga-like toxins (SLT) I and/or II; 13% of Shigella, 7% of Campylobacterjejuni or enterotoxigenic E. coli (ETEC) and 4% enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), Salmonella, Giardia lamblia or Hymenolepis nana. Mixed cultures were found in 16% of cases during the first year and in 18% during the second. These were mainly combinations of C. jejuni, with ETEC or EAEC. In 78% of children with bloody diarrhea the episode was single event during the first two years of life, lasting on average seven days. Epidemiologically, the incidence of bloody diarrhea rose steadily during the first two years of life, with a significant decrease after the tenth month. Prevalence was affected by seasonality in all pathogens, except for EAEC that had an endemic frequency. In the case of Shigella and SLT-producing E. coli clustering of cases and isolation of serologically identical strains indicated that infections were the result of common source outbreaks.

Diarrhea, Infantile↗
PubMed1990

Clonal relationships among classic enteropathogenic Escherichia coli (EPEC) belong to different O groups.

Fifty Escherichia coli strains belonging to nine classic EPEC (enteropathogenic E. coli) O:H serotypes from infantile diarrhea were examined for enzyme polymorphism and typed according to their multilocus genotypes. They were further examined for lipopolysaccharide (LPS) patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining, for localized adhesion to HEp2 cells, and for their outer membrane protein (OMP) pattern. A very close relationship was detected among electrophoretic type, O:H serotype, biotype, LPS type, and OMP pattern. Most likely these characteristic EPEC groups (all type I) each represented bacterial clones, and furthermore they could be grouped into two genetically closely related clusters. In each cluster the only phenotypic character that differed among strains was the O antigen, which might suggest that the genetic background for the LPS side chains can be transferred horizontally among EPEC strains. The results support the idea that O:H serotyping is useful for studies of epidemiologic linkages between cases of EPEC diarrhea.

Bacterial Adhesion↗
PubMed1990

Risk of diarrhea during the first year of life associated with initial and subsequent colonization by specific enteropathogens.

The incidence of colonization by enteropathogenic, enterotoxigenic, enteroinvasive, and enterohemorrhagic Escherichia coli (detected by DNA hybridization with specific radiolabeled probes), Salmonella sp., Shigella sp., Campylobacter jejuni, and rotavirus was related to the presence of diarrhea in a cohort of 75 rural infants followed longitudinally during the first year of life. The study was carried out between August 1985 and February 1987 in the village of Lugar Sobre la Tierra Blanca, in the state of Morelos, 180 km southwest of Mexico City. Intestinal colonization by specific enteropathogens was followed with fecal cultures taken every fortnight and every time a child had diarrhea. Pathogens isolated from cultures taken in the 48 hours prior to the initiation of the diarrheal episode were considered to be associated with the disease. Diarrhea was detected in 82% of the children with initial isolation of enterohemorrhagic E. coli and in 64% of the children with enteropathogenic E. coli or Shigella sp. The risk of diarrhea associated with the initial isolation of other pathogens was lower, at 41% for rotavirus and approximately 25% for enterotoxigenic E. coli, Salmonella sp., and C. jejuni. Initial colonization by the enteropathogens studied, whether or not they were associated with diarrhea, prevented disease, but not colonization by the same organism, when the children were reinfected during the first year of life. Enteropathogenic E. coli adherence factor, human or porcine heat-stable enterotoxins, fimbrial colonization factor antigens, and Shiga-like toxins I and II were important pathogenic characteristics related to the presence of diarrhea and to protection against subsequent infection by the same organisms.

Campylobacter Infections↗