Evaluation of a simple pretreatment method devised for direct identification of pathogens from positive blood culture bottles

Abstract

While a variety of pretreatment methods have been considered in recent years involving the use of a mass spectrometer for the direct identification of pathogens from positive blood culture bottles, identification rates have remained unsatisfactory. It was considered that the presence of hemoglobin or other biological proteins might affect the direct identification of pathogenic causes with a mass spectrometer, contributing to a decline in identification rates. For this study, a pretreatment method using semialkaline protease was devised and evaluated to remove biological proteins. Of the blood culture bottles obtained from a clinic, 676 were used, which were shown to be positive for pathogens. The pretreated material was identified directly using a VITEK MS mass spectrometer (BMJ). The same or better results were obtained than those in previous reports; identification rates for Gram-positive bacteria were 99.5% at the genus level and 98.4% at the species level; for Gram-negative bacteria, 99.0% at both the genus and species levels; for fungi, 80% at both the genus and species levels, and 99.1% at all genera levels and 98.5% at all-species levels. The pretreatment method devised here is simple, inexpensive, and requires no special equipment or reagents, and preprocessing can be accomplished by washing alone. Moreover, since no alcohol or formic acid treatments are performed for samples whose pretreatment is completed in the first step, the pretreatment method seems to be highly versatile with potential additional related applications, including in conventional automatic identification equipment and simple identification kits.