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Biomedical subjects

S Stavric

Publications and source records attributed to S Stavric.

18 recordsLinked to original sources
PubMed1993

Intestinal colonization of young chicks with Escherichia coli O157:H7 and other verotoxin-producing serotypes.

The susceptibility of chicks to colonization with Escherichia coli O157:H7 and other verotoxin-producing serotypes was studied. The E. coli colonized the caeca of both broilers and layers after oral administration of the challenge. The extent of colonization was dependent on challenge dose, age of chicks at the time of challenge, breed of chicks and length of time after exposure. A rapid increase in caecal colonization and a decrease in crop colonization was evident during the first few hours after challenge, with a maximum in the caeca at 6 h. Escherichia coli persisted in caecal contents as well as on caecal walls throughout the course of the experiments (14 d), but at much lower levels compared with the 6 h post-challenge.

Aging↗
PubMed1992

Comparison of a competitive enzyme immunoassay kit and the infant mouse assay for detecting Escherichia coli heat-stable enterotoxin.

A commercial competitive enzyme immunoassay kit, Escherichia coli ST EIA, was compared with the conventional infant mouse assay for sensitivity and specificity in detecting E. coli heat-stable enterotoxin. Thirty-one of 46 strains of E. coli tested were positive by both assays, while 15 strains were negative. The sensitivity of the ST EIA kit was up to 64-fold lower than the infant mouse assay.

Animals↗
PubMed1991

Effect of avian intestinal microflora possessing adhering and hydrophobic properties on competitive exclusion of Salmonella typhimurium from chicks.

The role of adherence and hydrophobic properties of native gut microflora in competitive exclusion of salmonellas from chicks is reported. Pure bacterial strains were isolated from washed caeca of 3-d-old chicks which had been treated on the day of hatch with a microflora from salmonella-free adult birds. These strains, when added to known mixtures of pure cultures, improved the efficacy of the mixtures in protecting chicks against a challenge of 10(5) cfu of Salmonella typhimurium. Strains from washed caeca and from other sources were also screened for hydrophobic properties. Undefined microflora and strains freshly isolated from washed caeca and which were hydrophobic improved the efficacy of protective mixtures, while none of the combination of hydrophobic strains obtained from stored strains had any beneficial effect.

Animals↗
PubMed1991

Assessment of two commercial agglutination kits for detecting Escherichia coli heat-labile enterotoxin.

Two commercial agglutination kits, a reserved passive agglutination test (VET-RPLA) and a staphylococcal coagglutination test (Phadebact ETEC-LT Test), were compared with two cell culture assays (Y-1 and Vero) and GM1 ganglioside enzyme-linked immunosorbent assay (GM1-ELISA) for sensitivity in detecting Escherichia coli heat-labile enterotoxin (LT). Of 48 toxigenic strains, 23 were positive by all assays. One strain was negative only by the Phadebact test. Four strains, all LT-II producers, were positive by cell culture only. For LT-I detection, the Phadebact test was the least sensitive but was simple and rapid; VET-RPLA was simple, sensitive, and a good substitute for cell culture or GM1-ELISA.

Agglutination Tests↗
PubMed1978

Properties of an Escherichia coli cytotoxin.

Isoelectric focusing of a heat-labile cytotoxin of Escherichia coli H30 revealed the presence of two molecular variants, pI 7.2 and a comparatively small quantity of pI 6.8. Predominant component pI 7.2 had a molecular weight of 28,000, induced some fluid accumulation in rabbit ileal loops, and showed no morphological response in Y-1 cells but a strong cytotoxic effect on Vero cells.

Animals↗
PubMed1978

Stimulation of cyclic AMP secretion in Vero cells by enterotoxins of Escherichia coli and Vibrio cholerae.

The morphological response of Vero cells to Escherichia coli heat-labile enterotoxin was similar to that of cholera toxin and was accompanied by increases in the intracellular level of cyclic AMP. The effects of both enterotoxins were enhanced by the presence of phosphodiesterase inhibitor and inhibited by heat or specific antisera. Accumulation of cyclic AMP preceded the morphological response.

1-Methyl-3-isobutylxanthine↗
PubMed1978

Comparative studies of five heat-labile toxic products of Escherichia coli.

Five heat-labile, partially purified toxic products of Escherichia coli were distinguished by isoelectric focusing, molecular weight, and neutralization with homologous and heterologous antisera. Only two affected the morphology of Y-1 cells, induced fluid accumulation in rabbit ileal loops, and stimulated production of cyclic AMP in Vero cells; these two did not cross-neutralize and only one showed cross-neutralization with cholera antitoxin. The remaining three products were cytotoxic for Vero cells.

Bacterial Toxins↗
PubMed1977

Assay of Escherichia coli heat-labile enterotoxin with vero cells.

The continuous cell line of African green monkey kidney, Vero, showed characteristic morphological changes in response to culture filtrates from toxigenic strains of Escherichia coli. The response compared favorably with that of Y-1 (mouse adrenal) and CHO (Chinese hamster ovary) cells. Vero cells were the simplest and most economical to maintain in the laboratory.

Animals↗
PubMed1977

Vero response to a cytotoxin of Escherichia coli.

A cytotoxin was found in culture filtrates of a number of Escherichia coli strains that differed from the known heat-stable and heat-labile enterotoxins of E. coli. It was cytotoxic for Vero but not for Y-1 or CHO cells, and its effect on Vero was distinctly different from that of heat-labile enterotoxin. It was labile to heat and antigenically different from heat-labile enterotoxin, and membrane filtration indicated a molecular weight of 10,000 to 30,000.

Antigens, Bacterial↗
PubMed1977

A modified bioassay for heat-stable Escherichia coli enterotoxin1.

Infant mice were injected orally with preparations containing Escherichia coli heat-stable enterotoxin (ST) and Evans blue dye, and incubated at 22 degrees C. With enterotoxin-positive samples, the stomach was distended and contained essentially all of the dye. With enterotoxin-negative samples, the stomach remained normal in size and the dye passed freely into the intestines. The time required to obtain the maximum ratio of gut weight to body weight varied from 30 to 90 min and was dependent upon the concentration of enterotoxin. Heat-labile enterotoxin (LT) had no effect during this period. Based on these findings, the mouse incubation time was reduced from 4 h to 90 min, and the heating of test samples was retained only for confirmation of ST. The location of the dye and stomach distention served as an indicator of positive responses to ST. Incubation of the mice at room temperature (22 degrees C) was found satisfactory.

Animals↗
PubMed1975

The application of QAE-Sephadex for the purification of two staphylococcal enterotoxins. I. Purification of enterotoxin C2.

A new method developed for purification of enterotoxin C2 from Staphylococcus aureus strain 361 consisted of four steps: batchwise adsorption from culture supernatant on QAE-Sephadex; gel filtration on Sephadex G-100; chromatography on QAE-Sephadex using a buffer of constant pH and molarity; and gel filtration using a volatile buffer of constant pH and molarity; and gel filtration using a volatile buffer as the eluting solvent. The purified enterotoxin appeared homogeneous by gel immunodiffusion, gel chromatography and in the analytical ultracentrifuge, although an apparent heterogeneity was noted on QAE-Sephadex chromatography and polyacrylamide disc electrophoresis at pH 4.5. The emetic dose, ED50, by intravenous route in cynomolgus monkeys was 0.04 mug/kg of animal weight. Upon treatment with sodium dodecylsulfate, beta-mercaptoethanol and urea, enterotoxin C2 separated into 3 bands in sodium dodecylsulfate-electrophoresis. One band mol. wt 29000, and two bands of lower molecular weight were so close that they moved as a single zone. After elution from gels, the zone of lower molecular weight were so close that they moved as a single zone. After elution from gels, the zone of lower molecular weight oligopeptides emerged as a single peak at the same position as untreated enterotoxin C2 during gel filtration with buffer lacking thiol and denaturant, and gave a reaction of complete identify to enterotoxin C2 in Ouchterlony immunodiffusion. The results suggest that enterotoxin C2 is a mixture composed of intact polypeptide chains, mol. wt 29000, and two fragments cleaved in the disulfide region of molecular weight of approx. 15400 and 12800 linked by the single disulfide bond in the toxin molecule. Amino acid analysis indicates that enterotoxin C2 consists of 255 amino acid residues.

Amino Acids↗
PubMed1975

The application of QAE-Sephadex for the purification of two staphylococcal enterotoxins. II. Purification of enterotoxin A.

The last three steps described in the preceding communication Robern, H., Stavric, S. and Dickie, N. (1975) Biochim. Biophys. Acta 000,000-000) were utilized successfully for the purification of enterotoxin A. The enterotoxin appeared homogeneous by gel chromatography and in the analytical ultracentrifuge but showed two bands on polyacrylamide disc electrophoresis at pH 4.5. The emetic dose, ED50, by intravenous route in cynomolgus monkeys was 0.12 mug/kg of animal weight. After treatment with beta-mercaptoethanol, urea and sodium dodecylsulfate enterotoxin A formed one band corresponding to a molecular weight of about 27700 on sodium dodecylsulfate gel electrophoresis. Molecular-weight estimation by gel filtration gave a value of 26500. The amino acid composition data indicate that enterotoxin A consists of 241 amino acid residues.

Amino Acids↗
PubMedDate not supplied

Defined cultures and prospects.

Resistance of young chicks to Salmonella colonization can be increased by treating them with suspensions or anaerobic cultures of gut content from healthy, adult birds. Unfortunately, such treatments have an unknown bacterial composition and are therefore not acceptable to regulatory agencies in some countries. Efforts are continuing to identify components in the gut microflora that are involved in the protective process. The ultimate aim is to identify bacteria that may be used, either alone or in mixtures (defined cultures), as a prophylactic treatment of chicks against Salmonella colonization. Although much research has been done in this area, a defined culture treatment with a potency and stability equivalent to that of undefined culture has not been developed. Since the mechanism of protection is not clear, there are no reliable criteria for selecting potentially protective strains. The most effective mixtures contain large numbers of bacterial cultures (about 50 isolates). These mixtures are comparable to undefined faecal cultures in protecting chicks against challenge levels of up to 10(4) Salmonella/chick. However, they are not protective for turkey poults. Mixtures containing lower number of strains are generally less protective. It appears that obligate and facultative anaerobes from different genera are required for protection. Mixtures containing strains from only one genus, e.g. Lactobacillus or Bifidobacterium, are generally not effective. Maintenance of intestinal isolates on laboratory media, as well as in storage at -70 degrees C, results in a progressive decrease in their protective ability. The protective ability of mixtures or individual strains can be partially restored by in vivo passage. A promising criterion for isolating and/or screening potentially protective isolates is based on the adherence of native microflora to the caecal wall of treated chicks. Despite substantial efforts and some progress in the development of defined cultures, the prospects are not very encouraging. Until the exact mechanism of protection is elucidated, the basis for selecting the required strains will be difficult to define.

Animals↗
PubMedDate not supplied

Protection of chicks against Salmonella infection with a mixture of pure cultures of intestinal bacteria.

A mixture of 28 pure cultures was prepared from the organisms isolated from native gut microflora (fecal and cecal contents) of adult Salmonella-free birds. This mixture was orally administered to 1-day-old chicks and examined for its efficacy against challenge with 10(5) colony-forming units of nalidixic-acid-resistant Salmonella typhimurium in six consecutive trials during a 20-month period. The efficacy of the mixture, which was prepared for each trial from stored isolates, progressively decreased, while that from stored fecal content remained unimpaired. Twenty-three cultures in the mixture were tentatively identified as belonging to seven different genera; the genus of the five other cultures remained unknown.

Animals↗