In the current decade, the use of plant extracts for the green preparation of metal nanoparticles has garnered increasing attention due to their eco-friendliness, cost-effectiveness, and sustainability. In the current study, silver nanoparticles (AgNPs) were synthesized using the ethanolic extract of Circaea lutetiana for the first time. Thetotal flavonoid content (TFC) and total phenolic content (TPC)of the extract were analyzed by spectrophotometric methods. Fourier transform infrared (FT-IR) spectroscopy was employed to determine the functional groups involved in both the reduction and stabilization processes of AgNPs. The formation and optical properties of AgNPs were confirmed by Ultraviolet–Visible (UV–Vis) spectroscopy. The greenlysynthesized AgNPs were characterized by FT-IR, UV–Vis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and zeta potential analyses, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results confirmed that the AgNPs were spherical in shape with an average size of approximately 3.8 nm and showed a good crystalline nature. Additionally, the AgNPs exhibited significant antimicrobial activity against both Gram-positive and Gram-negative bacteria, demonstrating their potential as green antimicrobial agents.

Currently, in Kazakhstan, chemical agents and antibiotics are widely used for treatment and prevention of fish diseases at fish farms. The use of probiotics as an alternative to antibiotics can help reduce the spread of antibiotic resistance in this area. The aim of the present study was to isolate the intestinal lactic acid bacteria of wintering carps. We assume that such bacteria can have more adaptive properties and can be used as probiotics for growing carp juveniles at fish farms. A probiotic characteristic of 22 lactic acid bacteria isolated from Common carp intestines was studied. Universal primers were used to determine the sequence of 16S rRNA gene fragments of lactic acid bacteria (LAB). Phylogenetic relationships of the isolates were estimated using the neighbor-joining (NJ) method in Mega 6,0. All identified isolates can grow in temperature range from 10° C to 37° C and in presence of bile salt. The isolated bacteria were screened for antibacterial activity, resistance to bile, resistance to antibiotics and growth at low temperatures. All isolates were tested in vitro for their ability to inhibit the growth of Shewanella xiamenensis, Pseudomonas taiwanensis, Ps. aeruginosa and Aeromonas punctata. As a result, 7 isolates with strong antagonistic activity were selected. 16S rDNA gene sequencing identified 4 isolates as Lactobacillus fermentum, 2 - as L. casei/paracasei and 1 - as Pediococcus pentosaceus. Antibiotic resistance profile of selected strains was studied, too. This study is the first attempt for Kazakhstan to isolate and study the representatives of the normal intestinal microflora of commercial fish species. Selective strains could be potential probiotics for freshwater aquaculture practices in Kazakhstan.