An in-vitro comparison of MRSA sequestration in foam dressings

Introduction

The presence of Methicillin resistant Staphylococcus aureus(MRSA) within chronic wounds poses a risk to the patient and surrounding patients/caregivers. Sequestration of MRSA in a dressing would improve the infection status of the wound bed and decrease the risk of MRSA transmission.

This study looks at MRSA sequestration of foam dressings following absorption.

Methods

Six different foam dressings were assessed over 7 days compared to knotted gauze. Dressings (n=12) were placed on 15ml of MRSA inoculum containing 10⁶ cfuml^-1. 15ml of inoculum was added daily for 7 days in order to mimic a highly exuding wound.

On days 1, 3 and 7 dressings were transferred to agar plates and incubated overnight at 37˚C. Dressings were then removed from the agar plates and photographed for evidence of MRSA transfer from the dressing.

Samples of the inner material of each dressing were processed and remaining viable bacteria quantified. Additional samples of the inner core were fixed and visualized using Environmental Scanning Electron Microscopy (ESEM).

Results & Discussion

All dressings except the gauze control absorbed the 15ml MRSA inoculum supplied each day.

5 of the 7 dressings demonstrated comparable MRSA recovery to the gauze control. A 3 log increase in MRSA retention was observed Foam F compared to the other dressings tested. 

Upon transfer to agar, 4 of the foam dressings demonstrated improved retention over 7 days. The remaining 3 and gauze released MRSA onto the agar throughout the study.

In the ESEM microscopy, MRSA was observed within the inner core of Foam F. This contrasted with the other tested dressings which had MRSA on the outer layer.

Conclusion

Retention of MRSA through the recovery steps suggested that the inner core sequestered microorganisms as bacteria were not readily released. MRSA not released was assumed to be held within the foam technology.