Role of biofilm in Pseudomonas aeruginosa colonization and infection

Intraclonal variations of resistance and phenotype in Pseudomonas aeruginosa epidemic high-risk clone ST308: A key to success within a hospital?

Most multidrug-resistant (MDR) and extensively drug-resistant (XDR) P. aeruginosa strains belonged to epidemic high-risk (EHR) clones that succeeded worldwide in the context of hospital outbreaks. In order to study the intraclonal diversity in EHR P. aeruginosa, we selected clinical and environmental strains of the EHR clone ST308 that caused outbreak clusters over five years in a hospital and then persisted in the hospital environment during four additional years, causing sporadic infections. Unexpectedly, resistance phenotype was very diverse within the population, independently of the origin (environmental or human) and the period of isolation (during or after outbreaks). Most MDR/XDR strains belonged to clusters in pulsed-field gel electrophoresis (PFGE) while singleton strains instead displayed susceptible or moderately resistant phenotypes. High diversity was observed for motility and biofilm formation without correlation with the origin and the period. Resistance to biocides was not linked to epidemic success or to environmental persistence. Finally, the EHR clone ST308 did not display common adaptive traits, nor traits related to an origin or a period of isolation in the hospital. The major character of this EHR clone ST308 is its intraclonal diversity that probably warrants its adaptation and persistence in hospital whatever the conditions and therefore its epidemic behaviour. This diversity could result from adaptive radiation with the evolution of multiple lineages that fill available niches within a complex ecosystem such as a hospital.

Bactericidal activity and biocompatibility of ceragenin-coated magnetic nanoparticles

Background

Ceragenins, synthetic mimics of endogenous antibacterial peptides, are promising candidate antimicrobial agents. However, in some settings their strong bactericidal activity is associated with toxicity towards host cells. To modulate ceragenin CSA-13 antibacterial activity and biocompatibility, CSA-13-coated magnetic nanoparticles (MNP-CSA-13) were synthesized. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize MNP-CSA-13 physicochemical properties. Bactericidal action and ability of these new compounds to prevent Pseudomonas. aeruginosa biofilm formation were assessed using a bacteria killing assay and crystal violet staining, respectively. Release of hemoglobin from human red blood cells was measured to evaluate MNP-CSA-13 hemolytic activity. In addition, we used surface activity measurements to monitor CSA-13 release from the MNP shell. Zeta potentials of P. aeruginosa cells and MNP-CSA-13 were determined to assess the interactions between the bacteria and nanoparticles. Morphology of P. aeruginosa subjected to MNP-CSA-13 treatment was evaluated using atomic force microscopy (AFM) to determine structural changes indicative of bactericidal activity.

Results

Our studies revealed that the MNP-CSA-13 nanosystem is stable and may be used as a pH control system to release CSA-13. MNP-CSA-13 exhibits strong antibacterial activity, and the ability to prevent bacteria biofilm formation in different body fluids. Additionally, a significant decrease in CSA-13 hemolytic activity was observed when the molecule was immobilized on the nanoparticle surface.

Conclusion

Our results demonstrate that CSA-13 retains bactericidal activity when immobilized on a MNP while biocompatibility increases when CSA-13 is covalently attached to the nanoparticle.