Biomedical subjects
Publications and source records attributed to M van Schothorst.
Since 1974, tetracycline resistance in salmonellae of human and porcine origin has decreased nation-wide in The Netherlands. This decrease has coincided with the ban on incorporation of tetracycline in animal feeds.
Investigations on farms where botulism has occurred in cows showed that proteolytic Clostridium botulinum type B was present in newly made grass silages. Experiments were undertaken to study growth and toxin production of C. botulinum in grass. Of the strains tested only proteolytic strains of C. botulinum types A and B were able to produce toxin with grass as a substrate. Proteolytic strains of type B produced both medium (12S) and large (16S) toxin forms. The minimal water activity (aw) for toxin production at pH 6.5 and 5.8 was 0.94. At pH 5.3, toxin was produced at an aw of 0.985. These results indicate that proteolytic strains of C. botulinum (if present) may multiply and produce toxin in wilted grass silages.
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Determination of Staphylococcus aureus enterotoxin type B using ELISA is described. The ELISA is more sensitive than the micro-slide technique. The specificity of the determination of enterotoxin B depends on the specificity of the antisera used. Application of this new assay is evaluated and discussed.
Comparative studies carried out in four laboratories revealed that in the examination of frozen or fresh minced meat samples tryptone soya broth and glucose mineral salts medium used for pre-enrichment gave the same results as buffered peptone water. The three tetrathionate media (Cardiff formula, Difco and Oxoid) used for enrichment after pre-enrichment, yielded approximately the same number of positive samples and about the same number of frozen and cooled samples was found positive when data of all four laboratories were considered. Between laboratories a considerable variation in results was found. This indicates the necessity to conduct comparative trials in more than one laboratory to validate the use of a specific method for regulatory purposes.
The use of antimicrobial agents for growth promotion and therapy in the European Economic Community and the resulting public health problems are discussed. Methods for detection of residues based on microbiological criteria for acceptance are presented and evaluated.
For a period of three months in a relatively small area (Walcheren), various materials (meat and meat products, insects, seagull droppings, chopping-block scrapings from butcher's shops, effluent of sewage treatment plants, drains from butcher's shops and stools of patients) were examined again for the presence of Salmonella as a continuation of previous investigations. As had been the case in previous studies, S. typhimurium (27.5%), S. panama (22.2%) and S. brandenburg (9.2%) were the three most frequently isolated serotypes. The three most frequently isolated phage types of S. typhimurium were II 505 (62.1%) II 502 (5.3%) and I 650 (4.2%). The serotypes and phage types were present in almost all the materials examined which again emphasizes the fact that there are contamination cycles of Salmonella. These studies show that the route of contamination divides in the butcher's shops. Salmonella organisms carried with the meat from the slaughter-house find their way into the drains on the one hand, and through meat and meat products, to the consumer on the other. Moreover, the high degree of contamination of effluent is not in accordance with the small number of cases of salmonellosis in man.
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During a certain period various materials (pigs, foods, insects, seagull droppings, chopping-block scrapings from butcher's shops, effluents of sewage treatment plants and stools of patients) were examined for the presence of Salmonella at the same time in a relatively small area (Walcheren). Certain types of Salmonella (S. typhi murium type II 505, S. panama, S. infantis and S. brandenburg) were frequently isolated from almost all materials examined. This may indicate the existence of Salmonella contamination cycles: one may think of the cycle: slaughter animal (infected from the environment and/or by meal) - meat - consumer - patient or healthy carrier - effluent and surface water - insects, birds and rodents - slaughter animal or meat and possibly other foods - consumer.
The protein binding, the plasma half-life and the residue depletion of sulfamonomethoxine (SMM) after intramuscular administration were investigated in pigs, horses and cattle. Protein binding was weakly concentration-dependent. The bound fraction in plasma in the therapeutic range amounted to approximately 45, 40 and 50% for pigs, horses and cattle respectively, and the plasma half-lives were approximately 5.1, 5.7 and 3.1 hours respectively. SMM levels were less than 1 mug/g in muscle tissue after 36, 20 and 12 hours in pigs, horses and cattle respectively. In the kidney SMM levels were not less than 1 mug/g until 48, 60 (extrapolated) and 36 (extrapolated) hours respectively. In pigs and horses SMM residues in the injection site were extremely variable. In cattle, SMM disappearance from the injection site was more regular. SMM concentrations in pig, horse and cattle liver remained more or less constant in the latter part of the period investigated.
When poultry carcasses were examined immediately prior to deep freezing those which were contaminated with salmonellae were generally found to contain about 17/100 g skin. In two instances more than 1400 salmonellae/100 g skin were found to be present. After deep freezing and thawing a 5 fold reduction had occurred in the numbers of salmonellae present. A high positive correlation was found between the number of Salmonella organisms on the skin and that in the thaw water.
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Lactose broth and buffered peptone water proved to be equally effective as preenrichment media in the isolation of salmonellae from egg products. With tetrathionate bile brilliant green broth, incubated at 43 degrees C as enrichment medium, more samples were found to be positive than with selenite cystine broth incubated at 37 degrees C or 43 degreesC and selenite brilliant green broth incubated at 37 degrees C. As selective agar, brilliant green agar proved to be more reliable than bismuth sulfite agar. These results indicate that the ISO method for the isolation of salmonellae from meat and meat products can be successfully used for the examination of egg products.
Two series of experiments with artificially contaminated milk powder were carried out. In the first series the influence of storage on the minimal resuscitation time was studied. In the second series the influence of ox bile versus taurocholate as inhibitive substances in tetrathionate bile brilliant green broth was studied. The results clearly indicate that in a given population cells may be present which are injured to various degrees, and that studies to determine minimal resuscitation times may be complicated by this fact.
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