Search Results (4)

The gamma-hemolysin protein is one of the most common pore-forming toxins expressed by the pathogenic bacterium Staphylococcus aureus. The toxin is used by the pathogen to escape the immune system of the host organism, by assembling into octameric transmembrane pores on the surface of the target immune cell and leading to its death by leakage or apoptosis. Despite the high potential risks associated with Staphylococcus aureus infections and the urgent need for new treatments, several aspects of the pore-formation process from gamma-hemolysin are still unclear. These include the identification of the interactions between the individual monomers that lead to the formation of a dimer on the cell membrane, which represents the unit for further oligomerization. Here, we employed a combination of all-atom explicit solvent molecular dynamics simulations and protein–protein docking to determine the stabilizing contacts that guide the formation of a functional dimer. The simulations and the molecular modeling reveal the importance of the flexibility of specific protein domains, in particular the N-terminus, to drive the formation of the correct dimerization interface through functional contacts between the monomers. The results obtained are compared with the experimental data available in the literature. Full article

Methicillin-resistant Staphylococcus aureus (MRSA) is mostly found in Thailand in the hospital as a nosocomial pathogen. This study aimed to report the genetic characterization of a clinical community-acquired MRSA (CA-MRSA) isolate collected from hospitalized patients in Thailand. Among 26 MRSA isolates, S. aureus no. S17 preliminarily displayed the presence of a staphylococcal cassette chromosome mec (SCCmec) type IV pattern. The bacterial genomic DNA was subjected to whole-genome sequencing. Panton–Valentine leukocidin (PVL) production, virulence toxins, and antibiotic resistance genes were identified, and multi-locus sequence typing (MLST) and spa typing were performed. The strain was matched by sequence to MLST type 2885 and spa type t13880. This strain carried type IV SCCmec with no PVL production. Five acquired antimicrobial resistance genes, namely blaZ, mecA, Inu(A), tet(K), and dfrG conferring resistance to β-lactams, lincosamides, tetracycline, and trimethoprim, were identified. The detected toxins were exfoliative toxin A, gamma-hemolysin, leukocidin D, and leukocidin E. Moreover, there were differences in seven regions in CR-MRSA no. S17 compared to CA-MRSA type 300. In summary, we have reported the ST2885-SCCmec IV CA-MRSA clinical strain in Thailand for the first time, highlighting the problem of methicillin resistance in community settings and the consideration in choosing appropriate antibiotic therapy. Full article

Background: Bovine mastitis is one of the major infectious diseases in dairy cattle, resulting in large economic loss due to decreased milk production and increased production cost to the dairy industry. Antibiotics are commonly used to prevent/treat bovine mastitis infections. However, increased antibiotic resistance and consumers’ concern regarding antibiotic overuse make it prudent and urgent to develop novel therapeutic protocols for this disease. Materials and methods: Potential druggable targets were found in 20 mastitis-causing pathogens and conserved and unique targets were identified. Bacterial strains Staphylococcus aureus (ATCC 29213, and two clinical isolates CI 1 and CI 2) and Staphylococcus epidermidis (ATCC 12228, and two clinical isolates CI 1 and CI 2) were used in the present study for validation of an effective drug combination. Results: In the current study, we identified the common and the unique druggable targets for twenty mastitis-causing pathogens using an integrative approach. Furthermore, we showed that phosphorylcholine, a drug for a unique target gamma-hemolysin component B in Staphylococcus aureus, and ceftiofur, the mostly used veterinary antibiotic that is FDA approved for treating mastitis infections, exhibit a synergistic effect against S. aureus and a strong additive effect against Staphylococcus epidermidis in vitro. Conclusion: Based on the data generated in this study, we propose that combination therapy with drugs that work synergistically against conserved and unique targets can help increase efficacy and lower the usage of antibiotics for treating bacterial infections. However, these data need further validations in animal models of infection. Full article

Cytolytic pore-forming toxins including alpha hemolysin (Hla) and bicomponent leukotoxins play an important role in the pathogenesis of Staphylococcus aureus. These toxins kill the polymorphonuclear phagocytes (PMNs), disrupt epithelial and endothelial barriers, and lyse erythrocytes to provide iron for bacterial growth. The expression of these toxins is regulated by the two-component sensing systems Sae and Agr. Here, we report that a point mutation (L18P) in SaeS, the histidine kinase sensor of the Sae system, renders the S. aureus Newman hemolytic activity fully independent of Hla and drastically increases the PMN lytic activity. Furthermore, this Hla-independent activity, unlike Hla itself, can lyse human erythrocytes. The Hla-independent activity towards human erythrocytes was also evident in USA300, however, under strict agr control. Gene knockout studies revealed that this Hla-independent Sae-regulated activity was entirely dependent on gamma hemolysin A subunit (HlgA). In contrast, hemolytic activity of Newman towards human erythrocytes from HlgAB resistant donors was completely dependent on agr. The culture supernatant from Newman S. aureus could be neutralized by antisera against two vaccine candidates based on LukS and LukF subunits of Panton-Valentine leukocidin but not by an anti-Hla neutralizing antibody. These findings display the complex involvement of Sae and Agr systems in regulating the virulence of S. aureus and have important implications for vaccine and immunotherapeutics development for S. aureus disease in humans. Full article