Cystic fibrosis (CF) is a multisystem disease, but respiratory manifestations are the leading cause of morbidity and mortality. Staphylococcus aureus is one of the most common pathogens of CF patients particularly in patients of young age.
S. aureus is an important pathogenic bacteria associated with a huge variety of infections and multidrug-resistance. It’s able to persist and multiply in different environments and produce a wide variety of virulence factors, most of which are encoded by mobile genetic elements (MGE), such as bacteriophages and pathogenicity Islands.
The staphylococcal pathogenicity islands (SaPIs) are intimately related to certain helper phages, whose life cycles they parasitize. Following infection by a helper phage or SOS induction of a helper prophage, the PICI genome excises, using the PICI-coded integrases (int) and excision functions (xis), replicates extensively using its replicon, and is efficiently packaged into infectious particles composed of phage virion proteins. These events conform the ERP (excision-replication-packaging) cycle of the PICIs.
In this study, we are interested in SaPIs mobilization mechanism of 199 S. aureus strains isolated from cystic fibrosis patients. This mechanism is important because it allows the mobilization and dissemination of virulence factors encoded in this SaPIs. In particular, we focused on SaPIs induction mechanism. For it, we have classified the SaPIs presented in these isolates based on them integrase by PCR and southern-blot. Secondly, by sequence analysis of PCR products determined the regulation module, presented between int and xis genes. Moreover, by southern-blot analysis we have tested the SaPI induction by endogenous phages. Surprisingly, 28% of SaPIs were induced by endogenous phages. Finally, by mutagenesis and transcriptional fusions we determine the phage proteins capable of binding to SaPIs Stl and therefore responsible for their induction. Accordingly, for the first we characterize the mechanism mobilization used by endogenous phages to mobilize SaPIs.