Introduction. Osteomyelitis in most cases is the monomicrobial disease, which caused by various gram-positive bacteria. However, previous injury may contribute to formation of a microbial association. Presence of two or more pathogens in the infectious focus can significantly complicate the clinical picture of the disease. Kytococcus schroeteri is one of the rarest pathogens in clinical samples. Number of described cases of infections caused by this microorganism in the world is a bit more than twenty. Aim of research. Description of the first identified clinical case of post-traumatic osteomyelitis caused by the association of Kytococcus schroeteri and Enterococcus faecalis. Materials and methods. The cultures were obtained by bacteriological method from the wound discharge of the patient's shin. Identification of the bacterial cultures was performed using a VITEK MS mass spectrometer, and was confirmed the 16S rRNA gene sequencing. The morphological, tinctorial and biochemical features of the obtained cultures were established, and their sensitivity to antibiotics was also determined. Results. The clinical case was associated with the diagnosis "Chronic post-traumatic osteomyelitis of the left shin". Two types of microorganisms were isolated from the wound discharge, which were identified as Kytococcus schroeteri and Enterococcus faecalis using the MALDI ToF MS method. Sequencing of the 16S rRNA gene of the isolated bacterial cultures confirmed the results of MALDI-ToF mass spectrometry. Antimicrobial susceptibility for this microorganism was determined according to the criteria for the group of staphylococci according to the clinical guide "Determination of sensitivity to antimicrobial drugs (rev. 2021)". Conclusions. For the first time the mixt infection caused by two Gram-positive bacteria K. schroeteri and E. faecalis has been described. Such associations can enhance the pathogenic effects of each other, which may contribute the transition of the infection to a chronic form with a low probability of positive result of the bacteriological test. K. schroeteri is a representative of the normal microbiota of the skin, but this microorganism is able to cause various infections. The species K. schroeteri should be differentiated from other representatives of the order Micrococcales. At bacteriological examination, resistance to oxacillin is a suspicious sign indicating the possible assignment of a culture to species K. schroeteri. Due to the unavailability of current biochemical tests to differentiate K. schroeteri from related taxa, reliable identification of this species is recommended using MALDI-ToF mass spectrometry or 16S rRNA gene sequencing.
