[Model investigations of the impedance effectiveness conerning bacterial relevant to food hygiene]. / Modelluntersuchungen zur Impedanzwirksamkeit Lebensmittelhygienisch Relevanter Bakterienarten.

The impedance technique mostly meets today's requirements of microbiological rapid methods. At relatively high prime cost for the equipment the advantages are marked by low personnel and material costs as well as swiftness combined with highly flexible usage. The method is applicable for both quantitative and qualitative examinations but can fail occasionally in total count determination, especially if the sample material contains heterogeneous microbes. In model investigations with 53 strains of 17 different genera Enterobacteriaceae strains, Aeromonads and Enterococcus strains proved to be highly impedance effective. Lactobacillus strains and Pseudomonads as well as Staphylococcus aureus strains showed a low impedance effectiveness. Several strains, for example of the genera Micrococcus, Acinetobacter and Brochothrix, did not show any changes of the medium impedance under the chosen conditions. Criterion for characterization of impedance effectiveness was the impedance detection time starting with identical initial counts (10(3) cfu/ml). Impedance effectiveness of microbes was determined at highly varying degree by the parameters of generation time, lag-phase duration and relative activity. This can lead either to wrong negative (underestimations) or wrong positive (overestimations) results of bacterial count.

Model experiments to establish behaviour of Yersinia enterocolitica O: 9 strains in various types of fresh dry sausage.

In model experiments different kinds of raw sausages were inoculated with liquid cultures of virulent-plasmid-carrying clinical Yersinia (Y.) enterocolitica (e.) strains of the O: 9 serotype, doses being between 10(4) and 10(5) cfu g-1. The sausage samples were stored at 3-5 degrees C and 13-16 degrees C. During the first 10 d of storage the Y.e. plate count was detected with Desoxycholate-Citrate-Lactose-Sucrose Agar every day, later on in addition to it with phosphate buffer-enrichment and with enrichment according to Schiemann (1982) in intervals of several days' duration. The pH and aw values, the contents of salt and water were detected. The multitude of complexly acting factors and substances prevents obviously the proliferation of Y.e. in fresh dry sausages. Decay dynamics of Y.e. were found to be considerably affected by storage temperature. Cold storage, basically, had a conservation effect and thus delayed the dying process of model strains. Yersinia enterocolitica-contaminated fresh dry sausage may cause potential danger to consumers, because of relatively extended survival periods of the pathogen. Therefore, manufacturers are expected to observe most stringent hygienic rules of Good Manufacturing Practice.

[Model studies of psychrotrophia in Yersinia enterocolitica]. / Modelluntersuchungen zur Psychrotrophie von Yersinia enterocolitica.

Cold storage cannot permanently inhibit an undesirable growth of micro-organisms in food. Psychotrophic bacteria and fungi are of special interest in this context. Previous information concerning the ability of Yersinia (Y.) enterocolitica (e.) to grow at temperatures at or below 0 degrees C are insufficient. Therefore, adequate model investigations at temperatures from -1 to -5 degrees C were undertaken, using nearly 90 Y. strains of different origin. The plate-count dynamic in nutrient broth was studied for a period of 3 weeks. In order to characterize the dynamic of bacterial growth, the quotient (Q) between the Y. plate counts at both the end and beginning of the investigation was calculated. Each increase of the plate count to at least double the initial population was regarded as growth in the true sense. At the end of the examination, the percentage of strains with at least doubled initial plate count was, at -1 degrees C, about 85%, about 85% at -2 degrees C, 59% at -3 degrees C, nearly 16% at -4 degrees C, and about 13% at -5 degrees C. These results make it clear that there are numerous Y.e. strains that are able to grow at temperatures below 0 degrees C. Moreover, several strains can even grow at -5 degrees C.

[The amine-forming ability of Aeromonas spp]. / Zum Aminbildungsvermögen von Aeromonas spp.

Motile Aeromonas (A.) species are considered international more and more as potential food poisoning organisms. Their ability to produce biogenic amines, products of metabolism, which in case can cause a disease, was only searched insufficiently till now. 50 strains of the species A.hydrophila, A.sobria, A.caviae and the non-motile species A.salmonicida were included in the tests for amine producing potency. Qualitative investigations to the formation of histamine, tryptamine, and tyramine were ensued by the help of thin layer chromatography. Quantitative investigations were only done in respect of the production of tyramine, which had been proved qualitatively in several strains, while histamine and tryptamine were not produced. Concentrations of tyramine with foodhygienic relevance were found out partially.