Microbiology, Biofilm and Antibiotics

Prosthetic joint infections are generally caused by a variety of gram-positive and gram-negative micro-organisms. New species are continuously isolated, including anaerobes. The pathogenic mechanisms responsible for articular infections are well studied only for some bacteria, e.g. Staphylococcus aureus and Pseudomonas aeruginosa, while others are only partially understood. The most important virulence and microbiological factors involved in these infections are the bacterial adhesion on the native joint or prosthetic material and the biofilm production by bacteria involved in the infection. Biofilm formation is the result of a developmental programme of gene expression involving intracellular signalling, or quorum sensing. The biofilm consists of bacteria embedded within an extracellular polymeric matrix (EPS), which protects micro-organisms from environmental factors, including host immune responses and normal levels of conventional antimicrobial agents. Biofilm resistance is a multi-factorial mechanism, which makes biofilm eradication difficult to obtain, and thus most biofilm-related infections require prompt removal of the device. Some antimicrobials are better than others in treating biofilm-associated bacteria and new antibiofilm substances are now being developed by research.