The identification of Staphylococcus aureus factors required for pathogenicity and growth in human blood

Staphylococcus aureus is a human commensal but also has devastating potential as an opportunist pathogen. S. aureus bacteraemia is often associated with an adverse outcome. To identify potential targets for novel control approaches we have identified S. aureus components that are required for growth on human blood. An ordered transposon mutant library was screened, identifying 9 genes involved specifically in haemolysis or growth on human blood agar compared to the parental strain. Three genes (purA, purB and pabA) were subsequently found to be required for pathogenesis in the zebrafish embryo infection model. The pabA growth defect was specific to the red blood cell component of human blood, showing no growth difference compared to the parental strain on human serum, human plasma, sheep or horse blood. PabA is required in the tetrahydrofolate (THF) biosynthesis pathway. The pabA growth defect was found to be due to a combination of loss of THF-dependent dTMP production by the enzyme ThyA and an increased demand for pyrimidines in human blood. Our work highlights pabA and the pyrimidine salvage pathway as potential targets for novel therapeutics and suggests a previously undefined role for a human blood factor in the activity of sulphonamide antibiotics

Genomic and epidemiological evidence of a dominant panton-valentine leucocidin-positive methicillin resistant staphylococcus aureus lineage in Sri Lanka and presence among isolates from the United Kingdom and Australia

Objective: To undertake the first detailed genomic analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolated in Sri Lanka. Methods: A prospective observational study was performed on 94 MRSA isolates collected over a 4 months period from the Anuradhapura Teaching Hospital, Sri Lanka. Screening for mecA, mecC, and the Panton-Valentine leucocidin (PVL)-associated lukS-PV/lukF-PV genes and molecular characterization by spa typing was undertaken. Whole genome sequencing (WGS) and phylogenetic analysis was performed on selected multilocus sequence type (MLST) clonal complex 5 (CC5) isolates from Sri Lanka, England, Australia, and Argentina. Results: All 94 MRSA harbored the mecA gene. Nineteen spa types belonging to nine MLST clonal complexes were identified. Where origin of the sample was recorded, most isolates were from skin and soft tissue infections (70/91; 76.9%), with fewer causing bacteremia (16/91; 17.6%), empyema (3/91; 3.3%) and osteomyelitis (2/91; 2.2%). Sixty two (65.9%) isolates were PVL positive with the majority (56 isolates; 90.3%) belonging to a dominant CC5 lineage. This lineage, PVL-positive ST5-MRSA-IVc, was associated with both community and hospital-onset infections. Based on WGS, representative PVL-positive ST5-MRSA-IVc isolates from Sri Lanka, England and Australia formed a single phylogenetic clade, suggesting wide geographical circulation. Conclusions: We present the most detailed genomic analysis of MRSA isolated in Sri Lanka to date. The analysis identified a PVL-positive ST5-MRSA-IVc that is prevalent among MRSA causing clinical infections in Sri Lanka. Furthermore, this clone was also found among isolates from the United Kingdom and Australia