Staphylococcus aureus ST228 and ST239 as models for expression studies of diverse markers during osteoblast infection and persistence
Dafne Bongiorno1*, Nicolò Musso2*, Giuseppe Caruso3*, Lorenzo Mattia Lazzaro1, Filippo Caraci3,4, Stefania Stefani1 and Floriana Campanile1.
1Department of Biomedical and Biotechnological Sciences (BIOMETEC) - Medical Molecular Microbiology and Antibiotic Resistance laboratory (MMARLab ), University of Catania, 95125 Catania, Italy;
2 Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95125 Catania, Italy;
3Oasi Research Institute - IRCCS, 94018 Troina (EN), Italy;
4 Department of Drug Sciences, University of Catania, 95125 Catania, Italy;
* These authors equally contributed to the paper.
Corresponding Author:
Dafne Bongiorno
Department of Biomedical and Biotechnological Sciences (MMARL)
University of Catania
Via Santa Sofia, 97
95123 Catania, Italy
Tel: +39 095 4781238
Email: d.bongiorno@unict.it
Abstract
The ability of S. aureus to infect bone and osteoblasts is correlated to its incredible virulence armamentarium that can mediate the invasion/internalization process, cytotoxicity, membrane damage and intracellular persistence. We comparatively analyzed the interaction, persistence and modulation of expression of selected genes as well as cell viability in an ex-vivo model using human MG-63 osteoblasts of two previously studied and well-characterized S. aureus  clinical strains belonging to ST239-SCCmec III-t037 and ST228-SCCmec I-t041 clones at 3h and 24h post infection (p.i). ATCC12598 was used as control strain. Using Imaging Flow Cytometry analysis, we found that strains differently invaded osteoblasts after 3h and 24h: ATCC12598 internalized in 70% and 50% of cells, ST239-SCCmec III in 50% and 45% and ST228-SCCmec I in 30% and 20%, respectively. ST239-III, during the infection period, exerted a significative cytotoxic activity due to the over-expression ofhla and psm A and the increased expression of the genes involved in adhesion, probably due to the release and re-entry of bacteria inside MG-63 at 24h p.i. The lower invasiveness of ST228-I was also correlated with the non-cytotoxic activity inside osteoblasts. This clone was not able to activate a sufficient cellular reaction, and succumbed inside the MG-63 cells.
Keywords : MRSA, ST228, ST239, osteoblast, cross-talk mechanism, virulence toxin.