Biofilm-Forming Mechanisms in Diabetic Foot Syndrome Pathogens: Adhesive Properties and Interaction in Associations

Aim. To investigate the adhesive properties and biofilm-forming ability of diabetic foot syndrome pathogens, both individually and in associations, and to compare them with reference strains. Materials and methods. The material for the study was the content of lower extremity wounds in 41 patients presenting ischemic and mixed forms of diabetic foot syndrome which was used for isolation of pure cultures of microorganisms. The adhesive properties of the isolated pathogens were evaluated calculating the average adhesion index, erythrocyte participation coefficient and microbial adhesion index. The biofilm-forming abilities were assessed after biofilm formation in vitro by determining the optical density. The characteristics of both isolated strains and two- and three-component microbial associations were studied. The obtained results were compared with the corresponding indicators of the reference strains. Results. All pathogenic microorganisms isolated from patients' wounds had high adhesive properties according to the defined parameters while corresponding reference strains had low and medium adhesive properties. Two- and three-component mixtures of isolates of pathogens demonstrated significantly higher adhesive capabilities compared to the strains. Highly adherent strains of Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae demonstrated the highest optical density of microbial biofilms. The optical density of microbial biofilms formed by a mixture of isolates of Staphylococcus aureus and Candida albicans was also notably higher than formed both by the reference strains and by each microorganism species separately. Conclusions. Biofilm-forming microorganisms play one of the key roles in the pathogenesis of diabetic foot syndrome. Microorganisms isolated from chronic wounds in diabetic foot syndrome have significantly higher adhesive properties and biofilm-forming abilities which predicts their increased virulence compared to the corresponding reference strains. The microbial biofilms formed by the association of the isolated Staphylococcus aureus and Candidaalbicans strains demonstrated considerably higher optical density than those formed by their reference strains separately and in association. Thus, microbial associations of pathogens in diabetic foot syndrome may also have increased virulence compared to their pure cultures.