Abstract: We carefully organized 6 manuscripts, including 1 review and 5 research papers for the molecular microbiology diagnosis special issue, mainly about the diagnosis, treatment(resistance), prevention and control of clinical common bacterium, fungus and mycobacterium infections. The special issue focuses on the application research of molecular biology techniques in the direct detection of clinical specimens, genotyping, resistance gene research, antigen preparation,serological diagnosis and so on. Blood stream infection is a serious infectious disease, but blood cultures have the problem with long turn-around-time and low positive rate. The application of molecular biology techniques can be used to the detection of common or rare pathogenic bacteria, mycobacteria, fastidous bacteria for rapid identification and drug resistance analysis in the blood stream infection, which can shorten the turn-around-time.Clostridium difficile is a kind of important nosocomial infection pathogen which can cause antimicrobial-associated diarrhea. GeneXpert real-time fluorescence quantitation polymerase chain reaction (PCR) can directly detect Clostridium difficile infection and has the advantages of rapid detection, simple operation and so on.Candida glabrata can cause blood stream infection and other infections. It is a common invasive fungus in nosocomial infection with strong drug resistance. Microsatellite polymorphism offers a simple and rapid method for genotyping with resolution, which is higher than multilocus sequence typing (MLST). Therefore, microsatellite polymorphism can be the preferred choice for Candida glabrata genotyping in laboratory.In recent years, Candida albicans azole resistance has increasing trend. The expression of genes related to azole resistance and biofilm in Candida albicans suggests that ERG11 gene over expression for Candida albicans is an important mechanism of azole resistance. High expression of HWP1 genes is associated with Candida albicans biofilm formation.The carbopenem resistance mechanism of Klebsiella pneumoniae is mainly producing plasmid-mediated Klebsiella pneumoniae carbopenem 2 (KPC-2). Homologous recombination knockout bla_KPC-2 gene in clinical isolates of Klebsiella pneumonia establishes lambda red homologous recombination method of knocking out its drug-resistant gene bla_KPC-2 on plasmid contained by clinical Klebsiella pneumoniae drug-resistant strains reliably, which is helpful to further study on the carbopenem resistance mechanism of Klebsiella pneumoniae.On Preparation and serology diagnosis research of recombinant Mycobacterium smegmatis expressing rd ESAT-6 of Mycobacterium tuberculosis, the fusion proteins of Mycobacterium tuberculosis are successfully prepared in this study. The fusion protein has good specificity and sensitivity for the serological diagnosis among tuberculosis patients.

Key words: Molecular technique, Blood stream infection, Clostridium difficile, Candida glabrata, Candida albicans, Klebsiella pneumoniae, Mycobacterium tuberculosis