[Reliability of the Identification Result of Score Value ≧2.000 with the MALDI Biotyper: What Kind of Polymicrobial Species Are Included].

Identification of bacteria by using MALDI Biotyper is relevant at the species category if Score Value (SV) is not less than 2.000. However, in practical examination, the analysis by MALDI Biotyper frequently produces the multiple candidate bacterial species with SV ≥2.000. In this study, we analyzed the ratio of multiple results among 10,081 specimens and identified the species of bacteria with high frequency of multiple results. Our analysis indicated that 8,129 strains out of 10,081 strains examined from July 2015 to July 2017, showed multiple identification results with MALDI Biotyper, and that multiple result was obtained in 4.9% of gram positive cocci analysis, 5.8% of gram positive rods, 25.4% of gram negative cocci, 16% of gram negative rod, none of fungus. In particular, MALDI Biotyper analysis of Enterobacter spp. (E. cloacae, E. asburiae, E. kobei, etc.), Acinetobacter spp. (A. baumannii, A. nosocomialis, A. pittii etc.), Neisseria spp. (N. flavescens, N. perflava etc.) had high ratios of multiple results. Our data suggests that genetic homology among bacteria results in multiple results of bacteria identification. The mass spectrometer method is the rapid test for bacteria identification. However, for obtaining higher specificity, it is required to combine with other methods. Furthermore, systematic annotation of bacteria is highly recommended.

[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 ß-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.

[Evaluation of novel nucleic acid detection kit for Mycoplasma pneumoniae].

For diagnosis of Mycoplasma pneumoniae infection, highly sensitive and rapid diagnosis is important. Because antibiotics are limited for the treatment of M. pneumoniae infection. In this study, we evaluated new rapid nucleic acid detection kit for M. pneumoniae. This kit does not require excessive pretreatment of specimens and molecular diagnosis of M. pneumoniae is possible within 40 min. Using 120 nasopharyngeal specimens, we compared this kit with a commercially available molecular diagnostic reagent (LAMP). 51 of 120 cases were M. pneumoniae positive, and the results of both assays were all consistent. In addition, sequencing of 23S rRNA gene was performed on 51 cases positive for M. pneumoniae. As a result, macrolide resistance mutation (2063A>G) was observed in 19 cases (37.3%). The gene mutations estimated by this kit coincided completely with the sequencing. In conclusion, new rapid nucleic acid detection kit could detect M. pneumoniae with the same sensitivity as other molecular diagnostics, in a simple process.