Staphylococcus aureus is responsible for 60–70% infections of surgical implants and prostheses in Orthopaedic surgery, costing the NHS £120–200 million per annum. Its ability to develop resistance or tolerance to a diverse range of antimicrobial compounds, threatens to halt routine elective implant surgery. One strategy to overcome this problem is to look beyond traditional antimicrobial drug therapies and investigate other treatment modalities. Biophysical modalities, such as ultrasound, are poorly explored, but preliminary work has shown potential benefit, especially when combined with existing antibiotics.

Using a methicillin-sensitive S. aureus reference strain and the dissolvable bead assay, biofilms were challenged by a low-intensity ultrasound (1.5MHz, 30mW/cm2, pulse duration 200µs/1KHz) for 20 minutes and gentamicin. The outcome measures were colony-forming units/mL (CFU/mL) and the minimum biofilm eradication concentration (MBEC) of gentamicin. The mean number of S. aureus within control biofilms was 1.04 × 109 CFU/mL. There was no clinically or statistically significant (p=0.531) reduction in viable S. aureus following ultrasound therapy alone. The MBEC of gentamicin for this S. aureus strain was 256 mg/L. The MBEC of gentamicin with the addition of ultrasound was 64mg/L. Further studies confirmed that the mechanism of action was due to incomplete disruption of the extracellular matrix with subsequent metabolic stimulation of the dormant biofilm-associated bacteria due to increased nutrient availability and oxygen tension.

Low intensity pulsed ultrasound was associated with a 4-fold reduction in the effective biofilm eradication concentration of gentamicin; bringing the MBEC of gentamicin to within clinically achievable concentrations.

Nasal carriers of methicillin sensitive Staphylococcus aureus (MSSA) have an increased risk for health-care associated infections. There is currently no national screening policy for the detection of MSSA in the UK. This study aimed to: evaluate the diagnostic performance of molecular and culture techniques in MSSA screening, determine the cause of any discrepancy between the diagnostic techniques, and model the potential effect of different diagnostic techniques on MSSA detection in orthopaedic patients. Paired nasal swabs for PCR assay and culture of S. aureus were collected from a study population of 273 orthopaedic outpatients due to undergo joint replacement surgery.

The prevalence of MSSA nasal colonisation was found to be between 22.4–35.6%. The current standard direct culturing methods for detecting S. aureus significantly underestimated the prevalence (p=0.005), failing to identify its presence in ∼1/3 of patients undergoing joint replacement surgery.

Modelling these results to national surveillance data, it was estimated that 800–1200 MSSA surgical site infections could be prevented annually in the UK by using alternative diagnostic methods to direct culture in pre-operative MSSA screening and eradication programmes.