Genetically engineered microorganisms (GEMs) have emerged as promising tools for treating diseases, cancers, and microbial infections. This review discusses the development, applications, and impacts of genetically engineered bacteria and phages. The use of GEMs aims to address challenges such as antibiotic resistance, limited therapeutic options, and side effects of conventional treatments. Advances in synthetic biology and genetic engineering have enabled the creation of GEMs with enhanced capabilities in treatment, diagnosis, and drug delivery. GEMs are produced using various genetic engineering techniques, including CRISPR-Cas9, bacterial artificial chromosomes (BACs), plasmid transfection, phage infection, protoplast fusion, conjugate transfer, and transposition recombination. These methods allow for precise modification of microbial genomes, enabling the production of modified strains with desired properties. The CRISPR-Cas9 system is particularly effective for gene editing, offering flexibility and precision in modifying bacterial and phage genomes. Genetically engineered phages have been developed to target specific pathogens, including antibiotic-resistant bacteria. These phages can be used for therapeutic purposes, such as treating infections caused by multidrug-resistant bacteria. Additionally, GEMs have been used in vaccine development, where they can stimulate immune responses and provide long-lasting protection. Phages have also been engineered to deliver therapeutic agents, such as cytokines, enzymes, and bacterial metabolites, to target specific diseases. Genetically modified fungi have been explored for their potential in producing secondary metabolites with medicinal properties. These fungi can be modified to enhance their ability to produce useful substances, making them valuable in biotechnology and pharmaceutical applications. Similarly, genetically engineered probiotics have been developed to improve their safety, functionality, and effectiveness in treating diseases. These probiotics can be designed to tolerate stress, deliver therapeutic agents, and modulate immune responses. In conclusion, genetically engineered microorganisms offer significant potential in various medical and biotechnological applications. Their ability to overcome challenges in disease treatment, antibiotic resistance, and therapeutic delivery makes them promising candidates for future medical advancements. Continued research and development in this field are essential to fully realize the potential of GEMs in improving human health.Genetically engineered microorganisms (GEMs) have emerged as promising tools for treating diseases, cancers, and microbial infections. This review discusses the development, applications, and impacts of genetically engineered bacteria and phages. The use of GEMs aims to address challenges such as antibiotic resistance, limited therapeutic options, and side effects of conventional treatments. Advances in synthetic biology and genetic engineering have enabled the creation of GEMs with enhanced capabilities in treatment, diagnosis, and drug delivery. GEMs are produced using various genetic engineering techniques, including CRISPR-Cas9, bacterial artificial chromosomes (BACs), plasmid transfection, phage infection, protoplast fusion, conjugate transfer, and transposition recombination. These methods allow for precise modification of microbial genomes, enabling the production of modified strains with desired properties. The CRISPR-Cas9 system is particularly effective for gene editing, offering flexibility and precision in modifying bacterial and phage genomes. Genetically engineered phages have been developed to target specific pathogens, including antibiotic-resistant bacteria. These phages can be used for therapeutic purposes, such as treating infections caused by multidrug-resistant bacteria. Additionally, GEMs have been used in vaccine development, where they can stimulate immune responses and provide long-lasting protection. Phages have also been engineered to deliver therapeutic agents, such as cytokines, enzymes, and bacterial metabolites, to target specific diseases. Genetically modified fungi have been explored for their potential in producing secondary metabolites with medicinal properties. These fungi can be modified to enhance their ability to produce useful substances, making them valuable in biotechnology and pharmaceutical applications. Similarly, genetically engineered probiotics have been developed to improve their safety, functionality, and effectiveness in treating diseases. These probiotics can be designed to tolerate stress, deliver therapeutic agents, and modulate immune responses. In conclusion, genetically engineered microorganisms offer significant potential in various medical and biotechnological applications. Their ability to overcome challenges in disease treatment, antibiotic resistance, and therapeutic delivery makes them promising candidates for future medical advancements. Continued research and development in this field are essential to fully realize the potential of GEMs in improving human health.