The pervasive rise of antimicrobial resistance has reinvigorated scientific interest in plant‑derived compounds as alternative or complementary antimicrobial agents. Medicinal plants such as Andrographis paniculata, Rauwolfia tetraphylla, and other species exhibit diverse bioactive secondary metabolites that confer significant antimicrobial properties. In addition, plant tissue culture technology, particularly induction of callus cultures, can enhance the yield of such metabolites, mitigating constraints associated with slow plant growth and overharvesting. This manuscript integrates historical pharmacognostic knowledge with contemporary empirical research to assess and compare antimicrobial activity in natural plant extracts and their in‑vitro generated callus counterparts. Key methodologies for extraction, culture conditions, and antimicrobial evaluation (including disk diffusion and standardized assays) are examined, along with phytochemical characterization of active compounds. Results from multiple investigations reveal that callus extracts often exhibit higher phenolic and flavonoid content and enhanced antibacterial activity compared to leaf extracts, although variability exists depending on species and culture conditions. Furthermore, bioactive compounds such as andrographolide demonstrate efficacy against both Gram‑positive and Gram‑negative bacteria, with emerging data suggesting effects on resistant clinical isolates. Limitations in antifungal potency and variability among extraction protocols are also discussed. These findings support the integration of plant tissue culture and phytochemical screening as promising strategies for identifying novel antimicrobial agents amid escalating resistance patterns.

Biogas technology represents a mature yet continually evolving renewable energy pathway that integrates waste management with decentralized energy production. Small- and medium-scale biogas systems, particularly those utilizing animal manure and agricultural residues, remain central to sustainable energy strategies in developing and transitional economies. This article presents a comprehensive analytical synthesis of biogas plant design principles, feedstock characteristics, digestion performance, and environmental implications, with particular emphasis on simple and flexible biogas systems. Drawing upon foundational and contemporary literature, the study examines how substrate selection, pretreatment methods, digester configuration, and operational conditions are associated with variations in biogas yield and system stability. The review also explores environmental considerations, including greenhouse gas mitigation, waste valorization, and the role of biogas in flexible power generation contexts. By systematically integrating evidence from experimental studies, pilot-scale systems, and applied engineering designs, this manuscript identifies persistent research gaps related to performance variability, scalability, and contextual adaptation. The discussion highlights methodological limitations in existing studies and outlines directions for future research that emphasize system optimization, lifecycle assessment, and socio-technical integration. Overall, the article contributes a structured, critical perspective on biogas systems that supports informed design, policy development, and interdisciplinary research in renewable energy and sustainable waste management.