The article reviews the development and impact of genetically engineered microorganisms (GEMs) on human health, focusing on their applications in treatment, prophylaxis, drug delivery, and diagnosis. The authors discuss various methods of genetic engineering, including CRISPR-Cas9, bacterial artificial chromosomes (BACs), phasmid transfection, and phage infection. They highlight the potential of GEMs in treating diseases such as cancer, metabolic disorders, and inflammatory conditions. The article also explores the biosynthesis of modified strains, administration routes, and environmental effects. The authors conclude that GEMs are promising candidates for adjunctive treatment of diseases and cancers, emphasizing their safety, cost-effectiveness, and patient-friendliness. Additionally, the article covers the genetic modification of viruses, phages, fungi, and probiotics, detailing their specific applications and challenges.The article reviews the development and impact of genetically engineered microorganisms (GEMs) on human health, focusing on their applications in treatment, prophylaxis, drug delivery, and diagnosis. The authors discuss various methods of genetic engineering, including CRISPR-Cas9, bacterial artificial chromosomes (BACs), phasmid transfection, and phage infection. They highlight the potential of GEMs in treating diseases such as cancer, metabolic disorders, and inflammatory conditions. The article also explores the biosynthesis of modified strains, administration routes, and environmental effects. The authors conclude that GEMs are promising candidates for adjunctive treatment of diseases and cancers, emphasizing their safety, cost-effectiveness, and patient-friendliness. Additionally, the article covers the genetic modification of viruses, phages, fungi, and probiotics, detailing their specific applications and challenges.