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А. V. Hulai

Vynnychenko State Pedagogical University, Kirovohrad, Ukraine


Aim. The scientific literature contains scarce information concerning the influence of freshwater biocenosis components on E. rhusiopathiae pathogenic bacteria. Plants are one of the main links in the processes of self-purification, metabolism, and regulation of gas regime in aquatic ecosystems. The objective of the currant research is to investigate the reaction of E. rhusiopathiae bacteria cultures to the allelopathic effect of background plant species in freshwater reservoirs of Ukraine. This paper is the first to present the results of experimental studies of the reaction of E. rhusiopathiae cultures to the effect of lifetime secretions and decomposition products of Canadian elodea (Elodea canadensis). Methods. The research was conducted in vitro. Samples of E. canadensis were obtained from the sites of their in vivo growth (the Inhul River) in the summer period (June and July). The plant samples weighing about 15.0 grams were placed in 1.5 dm3 glass jars and filled with water from the water supply system after 48 hours of settling. Jars with the plants were kept in natural lighting conditions at the temperature of +20.0 ± 2.0º C. Seven days later, water samples with the lifetime secretions of plants were taken for biological testing. After the end of E. canadensis vegetation period (in October) fragments of the plants were extracted from riverside waters. Postmortem secretions were obtained by the method mentioned above. The samples were sterilized under vacuum conditions using cellulose filters with a pore diameter of ≤0.2 mcm. For biotesting, E. rhusiopathiae culture (VR-2 strain, var. IVM) was used, cultivated within 48 hours on the brain heart infusion broth (AES Chemunex, France) at the temperature of +36.7±0.3ºС. The reaction of E. rhusiopathiae cultures to the allelopathic effect of E. canadensis was studied in vitro. The concentration gradient of plant secretions during the experiment was created by the method of serial dilutions. After the inoculation of the bacteria cultures, the content of E. canadensis secretions in the experimental samples was 1:10, 1:100, 1:1000 and 1:10000. Control samples contained sterilized water from the water supply system and the bacteria cultures. The content of E. rhusiopathiae at the beginning of the experiment was similar in both experimental and control samples, which was achieved due to the same amount of inoculum and by using the same culture for their selection. Prepared samples were kept for 48 hours at the room temperature (+18…20ºC), and then the amount of colony forming units (CFU) of E. rhusiopathiae bacteria was determined. Results. The reaction of E. rhusiopathiae cultures to the impact of lifetime secretions and decomposition products of the E. canadensis plants was different. The most significant oppression of the cultures of the experimental bacteria type was observed in case of the high content of E. canadensis lifetime secretions in the environment. The difference in the content of bacteria in the experimental and control samples was: 6.91 times in the 1:10 dilution of secretions, 4.48 times in 1:100 dilutions, 1.53 times in 1:1,000 dilutions, and 1.19 times in 1:10000 dilutions. The rate of correlation (r) between the CFU density of E. rhusiopathiae and the concentration of E. canadensis secretions was r = -0.70. Reduction in the intensity of E. rhusiopathiae cultures oppression in the experimental samples is connected with the decreasing concentration of the filtrate of lifetime plants secretions in the environment. The density of E. rhusiopathiae cultures was significantly increased in case of the high content of destruction products of the experimental plant type in the environment. The amount of bacteria in the experimental samples exceeded their content in the control samples: by 11.29 times in 1:10 dilutions of filtrates; by 8.16 times in 1:100 dilutions; 5.60 times in 1:1,000 dilutions; 2.20 times in 1:10000 dilutions. A direct correlation between these indicators was established as r = 0.82. Conclusion. During the vegetation period, E. canadensis are capable of producing an allelopathic effect on E. rhusiopathiae bacteria, resulting in the decreasing density of bacteria cultures in case of the increasing content of the substances secreted by the plants. During the warm season, the shallow-water thickets of E. canadensis plants create unfavorable conditions for the development of E. rhusiopathiae pathogenic bacteria due to the secretion of biologically active substances. After the vegetation period, a significant amount of plant residues is accumulated in water reservoirs; they undergo the process of decomposition, involving a large number of different kinds of living organisms. The research has led to the conclusion that the process of E. canadensis remnants decomposition triggers the production of substances in the environment that cause an increase in density of E. rhusiopathiae cultures. Thus, freshwater ecosystems demonstrate topical and trophic types of ecological relations between E. canadensis plants and E. Rhusiopathiae and this fact partly explains the dynamics of the populations of this pathogenic bacteria species. While being in aquatic ecosystems, E. rhusiopathiae come into ecological relations with different types of living organisms, including plants that are able to influence significantly the existence of this type of pathogenic bacteria. The identified tendencies in the reaction of E. rhusiopathiae cultures to the allelopathic impact of freshwater E. canadensis plants should be taken into account during further research into the ecology of these bacteria and for the development of measures to prevent and combat the incidence of erysipelas in humans and animals.

Keywords: allelopathia, Erysipelothrix rhusiopathiae, Elodea canadensis, topical and trophic types of biocenotic relations

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