Antibacterial Activity of Delafloxacin and Polymyxin B Against Planktonic and Biofilm-Associated Bacteria

Abstract

Abstract Biofilm-associated infections are difficult to treat because bacteria growing in biofilms show increased tolerance to antibiotics compared with planktonic cells. In chronic wound infections, Staphylococcus aureus and Pseudomonas aeruginosa are com monly detected and can contribute to persistent infection. This thesis investigated the antibacterial activity of delafloxacin and polymyxin B against S. aureus and P. aeruginosa under planktonic and biofilm-associated conditions. The antibiotics were tested alone and in combination for MIC determination, time-kill assays, biofilm treatment assays, and scanning electron microscopy. The results showed that both antibiotics reduced bacterial viability, with stronger effects generally observed at higher concentrations. Planktonic cells were more affected than biofilm-associated cells, supporting the increased tolerance of bacteria growing in biofilms. Combina tion treatment reduced bacterial survival in several conditions and showed stronger effects than single-antibiotic treatments. SEM analysis showed dense bacterial at tachment in untreated biofilms, while treated S. aureus and P. aeruginosa biofilms showed reduced bacterial coverage and altered biofilm structure. Overall, the find ings suggest that delafloxacin and polymyxin B have antibacterial effects against both planktonic and biofilm-associated bacteria, but complete biofilm eradication was not achieved under the tested conditions.