[On the identification accuracy of MALDI-TOF MS influence of pretreatment methods, types of medium, coating skills, and preservation methods].

In bacterial identification by MALDI-TOF MS, there are many reports of usefulness concerning direct identification from blood culture and identification of bacteria which cannot be identified with automatic analysis equipment. On the other hand, there are very few studies that investigate how various conditions influence on identification accuracy, such as the type of medium used for bacterial isolation and pure culture, the pretreatment methods, the difference in coating technique, and preservation methods. Therefore, we examined 10 strains of 2 drug-resistant bacteria species and 9 strains of 1 unnormal bacterium species. As a result, no significant differences were found in accuracy of identifying all strains of the target bacteria incubated for 24 hours and changing the types of medium, the pretreatment methods, and the coating techniques. In particular, methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum β-lactamase (ESBL) producing Escherichia coli showed little change in the score value and the mass spectrum that assayed every 24 hours during the preservation period in all of the medium. In the case of Vibrio vulnificus , however, identification accuracy was decreased by the specific medium and storage conditions. It is suggested as this factor that the growth state of bacteria may have influenced the identification accuracy.