References
A novel in vitro wound biofilm model used to evaluate low-frequency ultrasonic-assisted wound debridement
Abstract
Objective:
Bacterial biofilms remain difficult to treat. The biofilm mode of growth enables bacteria to survive antibiotic treatment and the inflammatory reaction. Low-frequency ultrasound has recently been shown to improve healing in a variety of settings. It is hypothesised that ultrasound disrupts the biofilm leaving bacteria more vulnerable to antiseptic or antibiotic treatment. The objective of this study is to develop a realistic model to elucidate the effect of ultrasound on biofilms.
Method:
A novel in vitro wound biofilm model was developed. Biofilms of Staphylococcus aureus were casted in a semi-solid agar gel composed of either tryptic soy broth (TSB) or a wound simulating media (WSM; composed of Bolton broth with blood and plasma), to resemble the non-surface attached aggregates. The model was used to evaluate the antibiofilm effect of an ultrasonic-assisted wound debridement device (UAW) in the presence of saline irrigation and treatment with a polyhexamethylene biguanide (PHMB)-containing antiseptic. Confocal microscopy was used to evaluate the effect of treatments on biofilm disruption and cell viability counting measured the antibacterial effects.
Results:
Confocal microscopy showed that application of 10 seconds of moderate-intensity UAW could effectively disrupt semi-solid biofilms grown on both media settings. This treatment only had a small effect on the cell viability. A 24-hour treatment with PHMB was able to reduce the number of bacteria but not eradicate the biofilm in both media settings. Interestingly, the efficacy of the PHMB antiseptic was significantly higher when applied on biofilms grown in the more complex WSM media. However, we found a significant improvement in reducing the number of viable bacteria grown on both media when applying UAW before administration of the PHMB solution. Applying UAW in the presence of PHMB further improved the efficacy.
Conclusion:
Using a realistic in vitro biofilm wound model, we show combining UAW with a PHMB-containing antiseptic has potential as an antibiofilm strategy in wound care.
The importance of biofilm growth is becoming increasingly renowned. It has been proposed that bacteria are predominantly growing as sessile communities rather than as single cells.1,2 Due to slower growth and build-up of matrix components, biofilms of most bacteria have been shown to become more tolerant to antimicrobials with age.3
It has been suggested that bacterial infections prevent wound healing.4 Data show that the presence of certain bacteria in these ulcers can induce enlargement and delay healing.5 Recent peptide nucleic acid fluorescent in situ hybridisation (PNA-FISH) analyses on sections from chronic wounds have shown that biofilm-growing bacteria can be identified, and possibly explain why the wounds persist.6,7,8 Fazli et al.7 have shown that the distance of the Pseudomonas aeruginosa biofilm to the wound surface was significantly greater than that of the Staphylococcus aureus biofilms, suggesting that the distribution of the bacteria in the chronic wounds is non-random. It is thought that bacteria located in the deeper regions of wounds may play a role in keeping the wounds arrested in a stage dominated by inflammatory processes.7
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