Characterization and validation of an alternative reference bacterium Korean Pharmacopoeia Staphylococcus aureus strain

The National Culture Collection of Pathogens (NCCP) is a microbial resource bank in Korea that collects pathogen resources causing infectious disease in human and distributes them for research and education. The NCCP bank attempts to discover strains with various characteristics and specific purposes to provide diverse resources to researchers. Staphylococcus aureus American Type Culture Collection (ATCC) 6538P is used as a reference strain in the microbial assay for antibiotics in the Korean and in the United States Pharmacopoeias. We aimed to analyze domestically isolated microbial resources from the NCCP to replace the S. aureus reference strain. Staphylococcus aureus strains were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and the VITEK-2 system and characterized by multilocus sequence typing, 16S rRNA sequencing, and antibiotic susceptibility testing. Several candidate strains had similar characteristics as the reference strain. Among them, the nucleotide sequence of the 16S rRNA region of NCCP 16830 was 100% identical to that of the reference strain; it was sensitive to six types of antibiotics and showed results most similar to the reference strain. A validity evaluation was conducted using the cylinder-plate method. NCCP 16830 presented valid results and had the same performance as ATCC 6538P; therefore, it was selected as an alternative candidate strain.