Introduction. Acinetobacter baumannii is a nosocomial pathogen that causes hospital-acquired infection in immunocompromised individuals and has multiple drug resistance. A. baumannii is the priority microorganism that requires new therapeutic alternatives to replace the use of antibiotics. Corynebacterium spp. may represent a promising therapeutic alternative, given the important role of individual representatives in microbiome-mediated defense against pathogens. The aim of the work is to investigate the antimicrobial activity of cell-free supernatants (CFSs) of Corynebacterium amycolatum against clinical isolates of A. baumannii. Materials and methods. The effect of CFSs of C. amycolatum on the growth of planktonic culture and biofilm formation of clinical isolates of A. baumannii was studied in 96-well polystyrene plates. The production of exopolysaccharides by A. baumannii after co-cultivation with CFSs of C. amycolatum was studied using the phenol-sulfuric acid method. The morphology of biofilms and the viability of test strains after preliminary treatment with CFSs of C. amycolatum were studied using scanning electron and fluorescence microscopy. The composition of the CFS of extract was studied using the GC-MS method. Results. An inhibitory effect of CFSs of C. amycolatum on the growth of planktonic culture of all A. baumannii test strains was established. With regard to biofilm formation, the effect of CFSs was multidirectional. SEM results showed that after co-cultivation with CFSs of C. amycolatum, A. baumannii cells were scattered over the glass surface, their cell membrane was not damaged. Using fluorescence microscopy, the absence of metabolic activity of most cells, characterizing their death, was detected. GC-MS analysis revealed the presence of 4 volatile compounds including 1,4-diaza-2,5-dioxo-3 isobutylbicyclo[4.3.0]nonane, 1,2-Benzenedicarboxylic acid, dibutyl ester, ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(phenylmethyl)-, (5'alpha)- and pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl)-. Conclusions. The obtained data on the antimicrobial and antibiofilm activity of C. amycolatum CFSs against A. baumannii are another argument indicating the probiotic properties of C. amycolatum. The identified chemical compounds in CFS open up the prospect for further research aimed at developing new strategies to combat infections caused by A. baumannii.

The presence of nontuberculous mycobacteria in biofilms on the surface of medical devices may affect the opportunistic pathogens that are common inhabitants of such biofilms. This study assessed the effect of Mycolicibacterium iranicum cell-free supernatants on biofilm formation and antibiotic susceptibility of Escherichia coli and Staphylococcus epidermidis differing in the anti-hemoglobin activity level. The cell-free supernatants have been shown to stimulate biofilm formation and also help reduce susceptibility of opportunistic pathogens to a number of antibiotics.