Different infections in blood leads to infectious diseases that are caused by viruses, bacteria and parasites. Microorganisms are used in the production of antibiotics, vaccines, steroids, etc. The advantages and limitation of molecular techniques including real-time polymerase chain reaction, genome sequencing, molecular typing, microarrays, PCR and multiplexing required advancements at molecular level. Nucleic acid-based tests are used in diagnosing infectious diseases for isolating nucleic acids from through gel electrophoresis, and nucleic acid hybridizationsn techniques to analyze DNA or RNA. Polymerase chain reaction (PCR) is an in situ DNA replication process that allows for the exponential amplification of target DNA in the presence of synthetic oligonucleotide primers. The advances in chemistry that made real-time PCR possible were also significant, and modifications of these chemical reactions continue today. In situ hybridization has been introduced into the clinical microbiology laboratory and should prove to be a useful technology for the rapid characterization of bacteria and fungi in positive blood culture samples. Multilocus sequence typing (MLST) is an unambiguous, portable and nucleotide-based technique for typing bacteria using the sequences of internal fragments of (usually) seven house-keeping genes. Microorganisms are used in the production of antibiotics, vaccines, steroids.