Bacteremia is a life-threating syndrome often caused by methicillin-resistant Staphylococcus aureus (MRSA). Thus, there is an urgent need to develop novel approaches to successfully treat this infection. Staphylococcal accessory regulator A (SarA), a global virulence regulator, plays a critical role in pathogenesis and β-lactam antibiotic resistance in Staphylococcus aureus. Hypericin is believed to act as an antibiotic, antidepressant, antiviral and non-specific kinase inhibitor. In the current study, we investigated the impact of hypericin on β-lactam antibiotics susceptibility and mechanism(s) of its activity. We demonstrated that hypericin significantly decreased the minimum inhibitory concentrations of β-lactam antibiotics (e.g., oxacillin, cefazolin and nafcillin), biofilm formation and fibronectin binding in MRSA strain JE2. In addition, hypericin significantly reduced sarA expression, and subsequently decreased mecA, and virulence-related regulators (e.g., agr RNAⅢ) and genes (e.g., fnbA and hla) expression in the studied MRSA strain. Importantly, the in vitro synergistic effect of hypericin with β-lactam antibiotic (e.g., oxacillin) translated into in vivo therapeutic outcome in a murine MRSA bacteremia model. These findings suggest that hypericin plays an important role in abrogation of β-lactam resistance against MRSA through sarA inhibition, and may allow us to repurpose the use of β-lactam antibiotics, which are normally ineffective in the treatment of MRSA infections (e.g., oxacillin).

Antibiotic-resistant H. pylori was increasingly found in infected individuals, which resulted in treatment failure and required alternative therapeutic strategies. Daphnetin, a coumarin-derivative compound, has multiple pharmacological activities. The mechanism of daphnetin on H. pylori was investigated focusing on its effect on cell morphologies, transcription of genes related to virulence, adhesion, and cytotoxicity to human gastric epithelial (GES-1) cell line. Daphnetin showed good activities against multidrug resistant (MDR) H. pylori clinical isolates, with minimal inhibitory concentration (MIC) values ranging from 25 to 100 μg/mL. In addition, daphnetin exposure resulted in H. pylori morphological changes. Moreover, daphnetin caused increased translocation of phosphatidylserine (PS), DNA damage, and recA expression, and RecA protein production vs. control group. Of great importance, daphnetin significantly decreased H. pylori adhesion to GES-1 cell line vs. control group, which may be related to the reduced expression of colonization related genes (e.g., babA and ureI). These results suggested that daphnetin has good activity against MDR H. pylori. The mechanism(s) of daphnetin against H. pylori were related to change of membrane structure, increase of DNA damage and PS translocation, and decrease of H. pylori attachment to GES-1 cells.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections are life-threatening syndromes with few therapeutic options. The potential impact of bacteriophages on the persistent outcome has not been well studied. In this study, we investigated the role of a novel prophage (ϕSA169) in MRSA persistence by using a lysogen-free clinically resolving bacteremia (RB) isolate and comparing it to a derivative which was obtained by infecting the RB strain with ϕSA169, which has been lysogenized in a clinical persistent MRSA bacteremia (PB) isolate. Similar to the PB isolate, the ϕSA169-lysogenized RB strain exhibited well-defined in vitro and in vivo phenotypic and genotypic signatures related to the persistent outcome, including earlier activation of global regulators (i.e., sigB, sarA, agr RNAIII, and sae); higher expression of a critical purine biosynthesis gene, purF; and higher growth rates accompanied by lower ATP levels and vancomycin (VAN) susceptibility and stronger δ-hemolysin and biofilm formation versus its isogenic parental RB isolate. Notably, the contribution of ϕSA169 in persistent outcome with VAN treatment was confirmed in an experimental infective endocarditis model. Taken together, these results indicate the critical role of the prophage ϕSA169 in persistent MRSA endovascular infections. Further studies are needed to identify the mechanisms of ϕSA169 in mediating the persistence, as well as establishing the scope of impact, of this prophage in other PB strains.IMPORTANCE Bacteriophages are viruses that invade the bacterial host, disrupt bacterial metabolism, and cause the bacterium to lyse. Because of its remarkable antibacterial activity and unique advantages over antibiotics, for instance, bacteriophage is specific for one species of bacteria and resistance to phage is less common than resistance to antibiotics. Indeed, bacteriophage therapy for treating infections due to multidrug-resistant pathogens in humans has become a research hot spot. However, it is also worth considering that bacteriophages are transferable and could cotransfer host chromosomal genes, e.g., virulence and antimicrobial resistance genes, while lysogenizing and integrating into the bacterial chromosome (prophage), thus playing a role in bacterial evolution and virulence. In the current study, we identified a novel prophage, ϕSA169, from a clinical persistent MRSA bacteremia isolate, and we determined that ϕSA169 mediated well-defined in vitro and in vivo phenotypic and genotypic signatures related to the persistent outcome, which may represent a unique and important persistent mechanism(s).