The Combination of Low-Frequency Ultrasound and Antibiotics Improves the Killing of In Vitro Staphylococcus aureus and Pseudomonas aeruginosa Biofilms

Abstract

Due to an increase in underlying predisposing factors, chronic wounds have become an increasing burden on healthcare systems worldwide. Chronic infections often contain biofilm-forming bacteria, which are challenging to eradicate due to increased antibiotic tolerance; thus, new and improved therapeutic strategies are warranted. One such strategy is the combination of ultrasound and antibiotics. Therefore, this study aimed to investigate the combinatory effects of low-frequency (50 kHz) ultrasound delivered by specially designed ultrasound patches using flexible piezoelectric material, PiezoPaint™, in combination with antibiotics against biofilms with Staphylococcus aureus and Pseudomonas aeruginosa. The reduction in viable cells in S. aureus and P. aeruginosa biofilms was evaluated post-treatment with fusidic acid, clindamycin, ciprofloxacin, and colistin in combination with ultrasound treatment. Two-hour ultrasound treatment significantly increased the bactericidal effect of all four antibiotics, resulting in a 96–98% and 90–93% reduction in P. aeruginosa and S. aureus, respectively. In addition, an additive effect was observed when extending treatment to 4 h, resulting in >99% and 95–97% reduction in P. aeruginosa and S. aureus, respectively. These results contrasted the lack of effect observed when treating filter-biofilms with antibiotics alone. The combined effect of ultrasound and antibiotic treatment resulted in a synergistic effect, reducing the viability of the clinically relevant pathogens S. aureus and P. aeruginosa. The modularity of the specially designed patches intended for topical treatment holds promising applications as a supplement in chronic wound therapy. Further studies are warranted with clinically isolated strains and other clinically relevant antibiotics before proceeding to studies where safety and applicability are investigated.

Biofilm and wound healing: from bench to bedside

“…Although low-frequency ultrasound is not effective alone in killing biofilm-growing bacteria, it can be combined with antibiotics to enhance antibiotic transport across the biofilms by enhancing the sensitivity of biofilms to antimicrobial agents [ 141 ]. Studies have shown that this combination helps in the increased killing of P. aeruginosa and S. aureus associated biofilms and those caused by drug-resistant E. coli [ 142 , 143 ]. Employing ultrasonic therapy in the management of non-healing wounds is a promising non-invasive means to decrease bacterial bioburden.…”

Mechanisms of antibiotic resistance in Pseudomonas aeruginosa biofilms

“…Beyond looking for new compounds or non-antibiotics strategies, it would be sensible to strive to improve therapeutic antibiotic strategies already available, as well as PK/PD parameters, to overwhelm mutation selection like combination of antibiotics [ [120] , [121] , [122] , [123] , [124] ], innovative sequential regimens [ 125 , 126 ] or improved drug-delivered for topical administration [ 127 , 128 ] recently demonstrated by ultrasound patches [ 129 ]. Progress in new alternative therapeutic approaches like formulation of antibiotics on nanoparticles [ 130 , 131 ], novel anti-biofilm compounds, CRISPR gene editing technologies and photodynamic therapies [ [132] , [133] , [134] ] is necessary.…”

Exploring the Potential of Ultrasound Therapy to Reduce Skin Scars: An In Vitro Study Using a Multi-Well Device Based on Printable Piezoelectric Transducers

“…For example, PiezoPaint™-based patches have recently been used to deliver low-frequency ultrasound in combination with topical antibiotic application. The device has been shown to be highly effective in killing otherwise resistant biofilm-forming bacteria and thus could be used in the treatment of chronic wounds [18].…”