Negative Pressure Level and Effects on Bacterial Growth Kinetics in an in vitro Wound Model

Negative Pressure Wound Therapy (NPWT) has been widely adopted in wound healing strategies due to its multimodal mechanism of action. While NPWT's positive impression on wound healing is well-established, its effect on bacterial load reduction remains equivocal. This study investigates NPWT's efficacy in reducing bioburden using an in vitro porcine skin model, focusing on the impact of Staphylococcus aureus and Staphylococcus epidermidis. Custom-made negative pressure chambers were employed to apply varying negative pressures. Porcine skin was cut into 5 × 5 cm squares and three standardized wounds of 6 mm each were created using a biopsy punch. Then, wounds were infected with S. aureus and S. epidermidis bacterial suspensions diluted 1:10,000 to obtain a final concentration of 1.5 × 10⁴ CFU/ml and were placed in negative pressure chambers. After incubation, bacterial counts were expressed as colony-forming units (CFU) per ml. For S. aureus at 120 hours, the median CFU, mean area per colony, and total growth area were notably lower at -80 mmHg when compared to -250 mmHg and -50 mmHg, suggesting an optimal negative pressure for the pressure-dependent inhibition of the bacterial proliferation. While analyzing S. epidermidis at 120 hours, the response to the negative pressure was similar but less clear, with the minor CFU at -100 mmHg. The influence of intermittent negative pressure on the S. epidermidis growth showed notably lower median CFU with the interval therapy every hour compared to the S. aureus control group. This study contributes valuable insights into NPWT's influence on the bacterial load, emphasizing the need for further research to reformulate its role in managing contaminated wounds.