Morphological Study of the Culture of Brucella Suis under Different Low-Temperature Storage Conditions

Introduction. Brucellosis is a dangerous zoonotic disease indirectly and directly transmitted from animals to humans. Failure to comply with the veterinary requirements and rules in keeping animals and selling livestock products may result in a persistently adverse epizootic situation on brucellosis that can be prevented by timely vaccination. Vaccine efficacy may be affected by various factors, primarily by vaccine strain properties, which may change under adverse conditions (e.g. long-term storage). To mitigate the destructive effect of freezing, the bacterial cells are placed in various media, and therefore it is important to verify at morphological level the preservation of the structures of bacterial cells. However, no comprehensive morphological studies on the effect of various low-temperature storage conditions on the Brucella suis ultrastructure have been performed yet. The aim of the present research is to conduct a morphological analysis of bacteria Brucella suis (strain 22) to assess the features of the deep freezing effect on their ultrastructure in different conditions.
Materials and Methods. The study was conducted in 2024 at the Federal State Budgetary Scientific Institution “Federal Center for Toxicological, Radiation, and Biological Safety” (Kazan). The object of the study were suspensions of Brucella suis cells (strain 22) grown in different conditions. They were dehydrated and embedded in epoxy resins, then subjected to polymerization. The specimens for ultrastructural analysis were prepared according to the ultrathin section obtaining methodology, they were mounted using the lens-hoods, strained and viewed with a transmission electron microscope. Statistical processing of the research results was carried out in Statistica 6.0 and MS Excel programs using the Mann– Whitney test, with the initial significance level of α=0.05 and subsequent correction of significance level according to Bonferroni method (up to α=0.002).
Results. When assessing the effect of deep freezing on the ultrastructure of bacteria Brucella suis (strain 22) grown in skim milk and sucrose-gelatin media, no morphological differences from the native strain were found. Statistically significant differences from the native strain were revealed only in the group where freeze drying was used, but these differences were within the standard deviation.
Discussion and Conclusion. Based on the results of the morphological study on the effect of deep freezing on the ultrastructure of bacteria Brucella suis (strain 22), it can be concluded that skim milk and sucrose-gelatin are preferable media for low-temperature storage. In future, it is planned to study the features of the effect the other storage conditions have on the ultrastructure of genus Brucella bacteria to supplement the information in the strain data sheets. This work has an important practical value for creating the collections of microorganisms and developing diagnostic tools.

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