A clinical case of posttraumatic osteomyelitis associated with kytococcus schroeteri and enterococcus faecalis

Introduction. In most cases, osteomyelitis is the monomicrobial disease 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 markedly complicate the disease clinical picture. Kytococcus schroeteri is one of the rarest pathogens found in clinical samples. Slightly more than twenty described cases related to such infection have been recorded globally. The aim of the research was to analyse the first identified clinical case of post-traumatic osteomyelitis associated with Kytococcus schroeteri and Enterococcus faecalis. Materials and methods. The bacterial cultures were obtained from the wound discharge of the patient’s shin by the cultural method. Identification of the bacterial cultures was performed using a VITEK MS mass spectrometer followed by 16S rRNA gene sequencing. The morphological, tinctorial and biochemical features of the cultures obtained were established, and their antibacterial resistance 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, and identified as Kytococcus schroeteri and Enterococcus faecalis using the MALDI-ToF mass spectrometry method. 16S rRNA gene sequencing from the isolated bacterial cultures confirmed the MALDI-ToF mass spectrometry data. Antimicrobial susceptibility for this microorganism was determined according to the criteria for the staphylococcal group according to the clinical guide “Determination of sensitivity to antimicrobial drugs (rev. 2021)”. Conclusion. For the first time, the mixed 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 bacterium, which may contribute to transition of the infection to a chronic form with a low probability of positive cultural test. K. schroeteri is a representative of the normal skin microbiota, but this microorganism is able to cause various infections. The K. schroeteri species should be differentiated from other representatives of the order Micrococcales. At cultural examination, resistance to oxacillin is a suspicious sign indicating that the bacterial culture might be potentially assigned to K. schroeteri species. Due to the unavailability of current biochemical tests for differentiation K. schroeteri from related taxa, reliable identification of this species is recommended using MALDI-ToF mass spectrometry or 16S rRNA gene sequencing.