Antimicrobial and Antibiofilm Activities of Carvacrol, Amoxicillin and Salicylhydroxamic Acid Alone and in Combination vs. Towards a New Multi-Targeted Therapy.

The World Health Organization has indicated as a high-priority pathogen whose infections urgently require an update of the antibacterial treatments pipeline. Recently, bacterial ureases and carbonic anhydrases (CAs) were found to represent valuable pharmacological targets to inhibit bacterial growth. Hence, we explored the underexploited possibility of developing a multiple-targeted anti- therapy by assessing the antimicrobial and antibiofilm activities of a CA inhibitor, carvacrol (CAR), amoxicillin (AMX) and a urease inhibitor (SHA), alone and in combination. Minimal Inhibitory (MIC) and Minimal Bactericidal (MBC) Concentrations of their different combinations were evaluated by checkerboard assay and three different methods were employed to assess their capability to eradicate biofilm. Through Transmission Electron Microscopy (TEM) analysis, the mechanism of action of the three compounds alone and together was determined. Interestingly, most combinations were found to strongly inhibit growth, resulting in an additive FIC index for both CAR-AMX and CAR-SHA associations, while an indifferent value was recorded for the AMX-SHA association. Greater antimicrobial and antibiofilm efficacy of the combinations CAR-AMX, SHA-AMX and CAR-SHA against were found with respect to the same compounds used alone, thereby representing an innovative and promising strategy to counteract infections.