Lactobacillus species are widely recognized for their probiotic potential, focusing on their mechanisms of health benefits and protection. Here we conducted an in vitro investigation of the probiotic potential with a role in microbiome homeostasis of four strains: Lactiplantibacillus plantarum L6 and F53, Ligilactobacillus salivarius 1, and Lactobacillus helveticus 611. A broad spectrum of antibacterial and antifungal activity was determined. The strain-specific inhibition of Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, and saprophytic/toxigenic fungi makes them promising as protective cultures. DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic) acid) measurements showed that tested samples had strain-specific capacity for scavenging of radicals. The molecular base for the antioxidant potential of two lyophilized forms of active strains was investigated by electron paramagnetic resonance spectroscopy. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, with fractions of the most active postbiotics obtained by SEC-FPLC (fast protein liquid chromatography) analysis, showed a wide variety of effects on the growth of a K562 myeloid leukemia cell line. The IC₅₀ (half-maximal inhibitory concentration) of L. salivarius 1 was determined to be 46.15 mg/mL. The proven in vitro functionality of the selected lactobacilli make them suitable for development of target probiotics with specific beneficial effects expected in vivo. Further investigations on produced postbiotics and safety have to be completed before they can be considered as scientifically proven probiotic strains.

Vibrio cholerae non O1 26/06, a non-pathogenic strain, was subjected to treatment by different concentration of paraquat (PQ) and H₂O₂. Exposure to PQ for 1 h caused induction of reactive oxygen species (ROS) such as superoxide anion radical (^•O₂⁻) and H₂O₂. At the same time, second stress factor significantly inhibited ^•O₂⁻ production and enhanced the intracellular H₂O₂ content. The enhanced ROS generation resulted in a significant increase in the levels of oxidatively damaged proteins in comparison to the control variant. Thus, the exposure of V. cholerae cells to PQ and H₂O₂ promoted oxidative stress. Cell response against this stress includes activation of antioxidant enzyme defence. The treatment with PQ concentrations in the range of 0 - 5 mM resulted mainly in activation of SOD, but not noticeably changed CAT activity in V. cholerae non-O1 26/06. In contrast, effect of H₂O₂treatment on antioxidant enzyme synthesis in our Vibrio strain was still much more pronounced for CAT than for SOD. Therefore, oxidative stress responses induced by ^•O₂⁻ (generated intracellularly by PQ) and H₂O₂ demonstrated differential adaptation of Vibrio cells to different toxic agents.

Fungal infections are a significant global public health challenge because of their widespread occurrence, morbidity, and profound social and economic consequences. Antifungal resistance is also an increasing concern, posing a substantial risk to public health. There is a growing interest in searching for new antifungal drugs isolated from natural sources. This study aimed to evaluate the antifungal activity of novel mollusk fractions against fungal strains resistant to nystatin and amphotericin B. In addition, the role of oxidative stress in the mechanism of damage was determined. The mucus from the garden snail Cornu aspersum (MCa/1-20) and the hemolymph fraction from the marine snail Rapana venosa (HLRv/3-100) were obtained and characterized via 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric -analyses. The results demonstrate that the spores and biomass of both mollusk fractions have a significant fungicidal effect against Penicillium griseofulvum, and Aspergillus niger. Compared to the control group, the release of intracellular proteins and reducing sugars was significantly increased in the treated groups. The data showed increased levels of oxidative stress biomarkers (lipid peroxidation and oxidatively damaged proteins) and a downregulated antioxidant enzyme defense, corresponding to increased antifungal activity. To our knowledge, this is the first study evaluating oxidative stress as a factor in mollusk fractions’ antifungal activity.

Nanotechnology has emerged as a promising option in combating the worsening situation with antibiotic resistance. We studied the antimicrobial effectiveness of four types of green synthesized zinc oxide nanoparticles (ZnO-NPs), obtained via Pluronic-assisted co-precipitation by lavender and thyme essential oils and their praseodymium-doped variants. Resazurin Microtiter Assay was applied to a panel of Gram-positive and Gram-negative bacteria from Risk 1 and 2 groups and the ESKAPE group. In relation to the pro-oxidative features of the ZnO-NPs, the production of superoxide dismutase (SOD) and catalase (CAT) in the tested microorganisms was also investigated, as these enzymes are important participants in the antioxidant defense of the bacterial cell and are considered virulence factors. We hypothesized that the sensitivity of microorganisms to the action of ZnO-NPs is related to their innate levels of antioxidant enzyme activity. The results showed that all types of studied ZnO-NPs had an antibacterial effect against the entire panel of tested strains, but with different potencies. The strongest effect was found for Arthrobacter nicotianae, Oerskovia paurometabola, Bacillus subtilis, and Escherichia coli. Less inhibition was observed for bacteria from Risk group 2 maybe due to their better antioxidant protection, especially for Pseudomonas aeruginosa. Praseodymium doping contributed to enhancing the bactericidal effect. A correlation between susceptibility of bacteria to ZnO-NPs and their antioxidant enzyme activity was observed.

Sialidases (neuraminidases) catalyze the removal of terminal sialic acid residues from glycoproteins. Novel enzymes from non-clinical isolates are of increasing interest regarding their application in the food and pharmaceutical industry. The present study aimed to evaluate the participation of carbon catabolite repression (CCR) in the regulation of cold-active sialidase biosynthesis by the psychrotolerant fungal strain Penicillium griseofulvum P29, isolated from Antarctica. The presence of glucose inhibited sialidase activity in growing and non-growing fungal mycelia in a dose- and time-dependent manner. The same response was demonstrated with maltose and sucrose. The replacement of glucose with glucose-6-phosphate also exerted CCR. The addition of cAMP resulted in the partial de-repression of sialidase synthesis. The CCR in the psychrotolerant strain P. griseofulvum P29 did not depend on temperature. Sialidase might be subject to glucose repression by both at 10 and 25 °C. The fluorescent assay using 4MU-Neu5Ac for enzyme activity determination under increasing glucose concentrations evidenced that CCR may have a regulatory role in sialidase production. The real-time RT-PCR experiments revealed that the sialidase gene was subject to glucose repression. To our knowledge, this is the first report that has studied the effect of CCR on cold-active sialidase, produced by an Antarctic strain.