[Direct identification of bacteria in blood cultures by MALDI-TOF MS]

Early and causal administration of antibiotics in patients with a positive blood culture is an essential prerequisite for successful treatment of infection. However, isolation and subsequent identification of bacteria in a blood culture by classical (culture) methods may last several days. MALDI-TOF MS is a method allowing rapid identification of bacteria, not only cultures from culture media, but also directly in clinical specimens.

The study included samples of positive blood cultures taken from patients in the University Hospital Olomouc between 2016 and 2018 and examined at the Department of Microbiology of the Faculty of Medicine, Palacký University Olomouc. Positive blood culture samples were processed using an in-house method involving the removal of blood cells by low-speed centrifugation. Subsequently, a pellet obtained by high-speed centrifugation and sample washing was tested by MALDI-TOF MS.

A total of 110 positive blood cultures were examined using the method of direct identification. At a species level, more Gram-negative bacteria (88 %) than Gram-positive bacteria (79 %) were correctly identified, with higher identification score values being obtained for the former. Identification score values of 2.0 or higher were found in 62 % of blood cultures containing Gram-negative bacteria and 17 % of blood cultures containing Gram-positive bacteria. Identification score values ranging from 1.7 to 2.0 were found in 21 % of Gram-negative blood cultures and 33 % of blood cultures containing Gram-positive bacteria.

Direct identification of microorganisms from positive blood cultures using MALDI-TOF MS enables more rapid diagnosis. By reducing the time required to obtain the result of pathogen identification, it may positively affect the antibiotic treatment of patients.