The transition between sessile and motile bacterial lifestyles

PhD ceremony: Ms. E. Tsompanidou, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The transition between sessile and motile bacterial lifestyles

Promotor(s): prof. J.M. van Dijl

Faculty: Medical Sciences

Staphylococcus aureus is one of the five most common causative agents of nosocomial infections. This bacterium is notorious for causing post-surgical wound infections, and chronic infections due to the formation of biofilms on indwelling medical devices . Pathogenic bacteria, such as S. aureus, utilize many different mechanisms to escape the host immune defenses, to establish themselves on the site of infection, and to invade different niches in order to find new sources of nutrients. The research presented in this thesis was specifically focused on two of these mechanisms, namely surface translocation and biofilm formation. Specifically, it was observed that only strains with an active agr locus can spread, whereas strains where the agr locus remains silent are unable to spread. Further analyses revealed that the agr-regulated phenol-soluble modulins (PSMs) are promoting colony spreading of S. aureus on wet surfaces. Interestingly, PSMs also promote detachment of S. aureus cells from a biofilm. Moreover, cell-wall associated proteins with known roles in biofilm formation were found to be limiting factors for staphylococcal spreading over wet surfaces. Together, the present data imply that biofilm formation and spreading are opposing processes that define the sessile and motile lifestyles of staphylococci. Interestingly, community-acquired methicillin resistant S. aureus (MRSA) strains, which are highly capable of infecting healthy individuals outside healthcare settings, display high expression levels of agr and therefore also of PSMs. The present observations indicate that a combination of different approaches may be needed to successfully combat both the sessile and motile forms of S. aureus.