1. Differences between biofilm characteristics of MRSA and MSSA causing Orthopaedic implant infection.
Oduwole, K. O.; Hammerton, H.;
Onayemi, O. D.; Mccormack, D. J.;
Republic of Ireland

2. Introduction
Prosthetic joint infection by Staphylococcal organisms remains one of the most vexing problems in Orthopaedic surgery.
Previous studies have suggested potential correlations between levels of resistance to beta-lactam antibiotics and biofilm phenotype in these organisms.

3. Aims
The aims of this study were to assess the relationship between methicillin sensitivity and ability to form biofilm by orthopaedic staphylococcal isolates and to compare the results to those of staphylococcal reference strains.

4. Material and methods
Biofilm phenotypes of 31 each of Methicillin resistant staphylococcus aureus (MRSA) and Methicillin sensitive staphylococcus aureus (MSSA) isolates from infected orthopaedic implants were characterised.
Ability to form biofilm under standard and biofilm-inducing growth conditions was related to methicillin susceptibilities.
Case notes of affected patients were reviewed to record difficulty encountered in eradicating the infections and whether behavior of the isolates in laboratory setting have clinical correlation.

5. Results
There was significant association between methicillin resistance in the isolates and their capacity to produce biofilm.
Nacl and glucose when compared to MSSA twice induced biofilm formation in MRSA.
There was a statistically significant association between a prosthetic infection-associated S.Aurues isolates and the presence of the ica gene cluster.
Clinical MRSA isolates were more induced by glucose rather than Nacl; in contrast the reference strains were strongly induced by Nacl and not glucose.

6. Clinical significance
Alteration of biofilm growth is a potential non -antibiotic way of controlling implant related infection.
This study suggest that regulatory pathways controlling biofilm phenotype in reference strains may be different from those used by clinical isolates, therefore results derived from use of reference strains should be interpreted with caution.