Effects of Freezing Milk Samples on the Recovery of Alimentary Pathogens and Indicator Microorganisms

The objective of the present study was to determine the effects of freezing and subsequent storage on quantitative results of bacteriologic culturing of selected alimentary pathogens and indicator microorganisms in milk. Two model experiments were carried out. In the first experiment, raw milk samples were frozen and stored at -20 °C for 72 hours, 7 days or 21 days. After thawing, the following counts of indicator microorganisms were assessed: total bacteria count and counts of coliform and psychrotrophic microorganisms. The counts of these microorganisms determined before freezing served as control. In the second experiment, milk samples were inoculated with strains of shigatoxigenic Escherichia coli, enterotoxigenic Staphylococcus aureus and bacteria Listeria monocytogenes and frozen. After storage for the above times, recovery was performed and colony-forming unit counts per millilitre were assessed. It was documented that freezing had a considerable adverse effect on the recovery of shigatoxigenic E. coli (P P P E. coli and psychrotrophic microorganisms continued with the time of storage - 72 hours and 7 days (P P L. monocytogenes and total bacterial count. Freezing caused a slight increase (P S. aureus counts in milk samples after 72 hours and 7 days of storage. The results of this study indicate that the freezing of milk samples is unsuitable for sample storage before the assessment of hygienic quality because potential risk of misdiagnosis may be high

Problems of epitypification in morphologically simple green microalgae: a case study of two widespread species of Klebsormidium (Klebsormidiophyceae, Streptophyta).

The extensive genetic cryptic diversity revealed by molecular studies in many green microalgae has caused great uncertainties in the circumscription of some species described on strictly morphological grounds. These uncertainties should be resolved by obtaining molecular data from type materials, but this procedure is not feasible in many species because the type specimens are illustrations, or too small or poorly preserved to obtain DNA sequence data. In these situations, the selection of an epitype is often a mandatory requirement to define the identity of a species and establish unambiguously its position in molecular phylogenies. In this study we investigated the identity of two widespread species of Klebsormidium (Streptophyta), K. flaccidum and K. nitens, which were recently epitypified by Mikhailyuk and colleagues. We collected several specimens of these algae from the type localities and the original habitats of these two species, for which we examined morphology in the field material and in culture, and obtained sequences of the rbcL gene. On the basis of the original descriptions, we conclude that the designation of the epitype of K. flaccidum was correct, whereas the epitype of K. nitens (which consists of material collected tens of thousands of km from the type locality) was most probably incorrect. We discuss the implications of these decisions for the classification of Klebsormidium and, more generally, the importance of the correct choice of epitype material for the taxonomy of green microalgae