Assessing a potential to improve data quality for accelerated identification of microorganisms derived from positive blood cultures

Diagnostics of blood-borne infections is still an urgent problem of modern medicine. The main causative agents of septic conditions are gram-positive microorganisms particularly Staphylococcus aureus, enterococci, etc., whereas clinical significance of isolated coagulase-negative staphylococci is ambiguous. Escherichia coli, Klebsiella pneumoniae and other enterobacteria, as well as Acinetobacter baumannii prevail among the gram-negative flora. Modern possibilities of accelerated identification of microorganisms derived from positive blood cultures based on mass-spectrometry consist of two approaches. Firstly, the manufacturers’ developed consumables for mass spectrometry are proposed, and secondly, there are “domestic” developments of accelerated sample preparation protocols developed by microbiological laboratories. The approaches used have a number of advantages and disadvantages, but to summarize, the use of the proposed methods in routine practice is quite limited. At the same time, the need to accelerate the issuing a microbiological conclusion related to nosology is great being associated with improved outcomes. In this regard, the aim of the study was to evaluate convergence and accuracy of results for accelerated identification of microorganisms derived from positive blood cultures in blood-borne infections. The study included 87 positive blood cultures, the identification of pathogens from them occurred in four ways: the classical microbiological analysis of blood for sterility, pathogen identification directly from the vial without isolating a pure culture, as well as two sample preparation methods based on ethylenediaminetetraacetic acid (EDTA) and potassium ethylenediaminetetraacetate disubstituted (EDTA-K2) as wash additives. It was found that gram-positive and gram-negative flora were isolated from the blood almost evenly often. When evaluating an influence of biomaterial used for mass spectrometry, it turned out that use of wash additives increases chances of successful identification of bacteria from a blood sample. The influence of tinctorial properties on the results of determining the species assignment of isolates was also evaluated. Identification of gram-positive flora is more accurate, since some pathogens were not identified without washing additives, and when using EDTA-K2 and the corresponding acid, assignment to the genus was obtained in the same samples. A similar pattern was also characteristic of gram-negative flora. At the same time, modern manufacturers of laboratory equipment and reagents allow to standardize sample preparation procedures in the protocols used. The effects of EDTA-K2, which allowing to use it as a washing component, are associated with the binding of calcium and magnesium ions in solution, which reduces the adhesion of bacterial cells to blood cells, thereby contributing to better mass spectrometry of microbial sediments with accelerated identification of microorganisms from positive blood cultures. Thus, use of the described additives can provide high quality, timely and adequate diagnostics of serious and life-threatening conditions such as blood-borne infections.