Bacterial exopolysaccharides are homopolymeric or heteropolymeric polysaccharides with large molecular weights (10–1000 kDa). Exopolysaccharides' functional uses and potential have revolutionized the industrial and medicinal industries. Hence, the aim of the present study was to optimize the production of bacterial exopolysaccharide and apply it as a capping agent for selenium nanoparticles synthesis. Exopolysaccharide (EPS) producing Lactic acid bacteria (LAB) were isolated from dairy products then biochemically characterized and assessed for their potential antimicrobial effect. The most potent EPS producer was identified as Lactiplantibacillus plantarum strain A2 with accession number OP218384 using 16S rRNA sequencing. Overall, FTIR data of the extracted EPS revealed similarity with amylopectin spectrum. ¹H NMR spectrum revealed an α-anomeric configuration of the glycosidic linkage pattern in the polysaccharides while the ¹³C NMR spectrum can also be separated into two main portions, the anomeric carbons region (δ 98–102 ppm) and the non-anomeric carbons region (δ 60–81 ppm). Antimicrobial activity of the produced EPS showed maximum activity against Staphylococcus aureus, MRSA, Enterobacter aerogenes, Klebsiella pneumoniae and Candida albicans respectively. The EPS capsule layer surrounding the bacterial cells was detected by TEM study. Optimization of EPS production was evaluated using Taguchi design, trial 23 reported the highest biomass yield and EPS output (6.5 and 27.12 g/L respectively) with 2.4 and 3.3 folds increase (from the basal media) respectively. The optimized exopolysaccharide was used as a capping and stabilizing agent for selenium nanoparticles (EPS-SeNPs) synthesis. Zeta potential, size and PDI of the synthesized nanoparticles were − 19.7 mV, 45–65 nm and 0.446 respectively with strong bactericidal and fungicidal effect against the tested pathogens. Complete microbial growth eradication was recorded after 6, 8 and 10 h against Staphylococcus aureus, Candida albicans and Klebsiella pneumoniae respectively. EPS-SeNPs showed a potent antioxidant effect reached 97.4% and anticancer effect against A549 lung cancer cell line (IC₅₀ reached 5.324 µg/mL). EPS-SeNPs inhibited cancerous cell growth at S phase. Moreover, molecular studies revealed the anti-apoptotic activity of Bcl2's was inhibited and Bax was activated. The present investigation successfully synthesized selenium nanoparticles through bacterial EPS with significantly high antimicrobial and anticancer activity.

Microbial exopolysaccharides (EPSs) possess valuable biological functions and fascinating physicochemical properties. On the other hand, lung cancer is the primary contributor to global cancer-related deaths. However, health and safety concerns have prevented the identification and approval of any medications, including chemotherapeutic agents, for lung cancer treatment to date. The current study aims to enhance the production of bacterial EPS as a coating agent for the synthesis of selenium nanoparticles (AZEPS-SeNPs), to enhance their biological activity against pathogenic microbes, human lung adenocarcinoma cells (A549) in vitro, and diethyl nitrosamine (DEN)-induced lung cancer in vivo. The synthesized AZEPS-SeNPs exhibited a significant antifungal effect reaching 49.3 mm against Candida albicans. SeNPs and EPSs demonstrated a concentration-dependent synergistic antioxidant effect of 96.8%. Moreover, the synthesized nanoparticles showed a highly potent cytotoxic effect against A549 cells (1.724 ± 0.08 µg/mL) with a therapeutic index of 7.18 ± 0.21 that leads to increased reactive oxygen species (ROS) production. AZEPS-SeNPs demonstrated a proapoptotic effect on the lung adenocarcinoma A549 cell line by stimulating caspase 3 and Bax (7.08-fold and 6.505-fold, respectively), inhibiting the anti-apoptotic gene Bcl2, and arresting the cell cycle in the S phase. In vivo study revealed that the AZEPS-SeNPs-treated group showed improved histopathological examination of lung tissue sections. The present study concluded the efficiency of the synthesized bacterial EPS-SeNPs as multi-functional antimicrobial, anticancer and antioxidant agent.

Meningitis caused by Klebsiella pneumoniae and Pseudomonas aeruginosa has lately become a prevalent cause of the central nervous system (CNS) infection. Bacterial invasion into the subarachnoid space prompts the releasing mechanism of chemokines and pro-inflammatory cytokines. The present study aimed to compare K. pneumoniae and P. aeruginosa meningitis concerning the memory, pro-inflammatory mediators and brain histopathological changes at different time intervals in adult Albino rats. The animals were sacrificed at three time intervals comprising 5, 10 and 15 days after meningitis induction. Cerebrospinal fluid (CSF) culture, relative brain weights, complete blood analysis, biochemical markers, levels of cytokine, chemokine and brain-derived neurotrophic factor (BDNF), neurotransmitter acetylcholine esterase (AChE) activity, and the brain histopathology of the infected rats in comparison to those in the control group were assessed. There was a significant increase in the levels of pro-inflammatory cytokines and chemokines including TNF-α, IL-1β, IL-6 and AChE after 5 days of bacterial meningitis infection with both K. pneumoniae and P. aeruginosa. The histopathological analysis of the cerebral cortex in the P. aeruginosa meningitis model at different time intervals revealed abundant numbers of dilated and congested blood vessels with severe hemorrhage, cerebral infarct, intracellular and extracellular vacuoles, and gliosis. Fifteen days post infection, a significant reduction in the brain tissue weight was observed. The meningitis model employing P. aeruginosa exhibited more evident time-dependent severity compared to K. pneumoniae, which may advocate its validity as a simple and effective research model to study meningitis of the CNS. This model may be utilized for further investigation to ascertain the molecular and biological association between bacterial meningitis and the development of the pathophysiological hallmarks underlying Alzheimer’s disease in preclinical and clinical setups. Clinical extrapolation based on studies employing animal disease models should be carefully interpreted.