Antibacterial and antibiofilm effects of radioactive thermal water

Objective: Most of the infections of the upper respiratory tract are caused by biofilm-forming microorganisms belonging to the Pseudomonas, Streptococcus, Staphylococcus, and Enterobacter genus. Many of these microorganisms also show antibiotic resistance, partly related to biofilm formation. The treatment of these affections may include inhalation of radioactive thermal water (RTW). The present study aimed to evaluate the in vitro antibiofilm effect of RTW collected from Merano springs, Italy. Materials and Methods: A series of experiments were performed evaluating the effect of RTW against planktonic cultures (1 h exposure) and on biofilms (10 min and 1 h exposure) formed by Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. Viable biomass was assessed using a colorimetric assay. A model based on the infection by the same strains of a reconstituted human respiratory epithelium (RHRE) was used to morphologically evaluate the antibiofilm effect of RTW. Results: RTW decreased the viability of S. aureus and S. pneumoniae planktonic cultures by about 20%. RTW also decreased biofilm viability by all strains except for E. coli at both time points. In the RHRE model, bacterial adherence and colonization occurred in all specimens, showing a particular affinity for the epithelium's cilia. Bacterial infections caused significant alterations in the epithelium structure, showing enlargement of the intercellular spaces, and damage to the cell structure. Specimens infected with S. aureus showed slightly lower colonization levels after RTW treatment. Conclusions: Results of this in vitro study showed a significant effect of RTW against Gram-positive planktonic bacterial cells as well as a significant antibiofilm activity.