Multi-omics based characterization of antibiotic response in clinical isogenic isolates of methicillin-susceptible/-resistant Staphylococcus aureus

We introduce clinical isogenic strain isolates and a multi-OMICS approach to observe a response to oxacillin of methicillin- susceptible/-resistant Staphylococcus aureus.

The Granuloma Response Controlling Cryptococcosis in Mice Depends on the Sphingosine Kinase 1–Sphingosine 1-Phosphate Pathway

Cryptococcus neoformansis a fungal pathogen that causes pulmonary infections, which may progress into life-threatening meningitis. In commonly used mouse models ofC. neoformansinfections, fungal cells are not contained in the lungs, resulting in dissemination to the brain. We have previously reported the generation of an engineeredC. neoformansstrain (C. neoformansΔgcs1) which can be contained in lung granulomas in the mouse model and have shown that granuloma formation is dependent upon the enzyme sphingosine kinase 1 (SK1) and its product, sphingosine 1-phosphate (S1P). In this study, we have used four mouse models, CBA/J and C57BL6/J (both immunocompetent), Tgε26 (an isogenic strain of strain CBA/J lacking T and NK cells), and SK−/−(an isogenic strain of strain C57BL6/J lacking SK1), to investigate how the granulomatous response and SK1-S1P pathway are interrelated duringC. neoformansinfections. S1P and monocyte chemotactic protein-1 (MCP-1) levels were significantly elevated in the bronchoalveolar lavage fluid of all mice infected withC. neoformansΔgcs1but not in mice infected with theC. neoformanswild type. SK1−/−mice did not show elevated levels of S1P or MCP-1. Primary neutrophils isolated from SK1−/−mice showed impaired antifungal activity that could be restored by the addition of extracellular S1P. In addition, high levels of tumor necrosis factor alpha were found in the mice infected withC. neoformansΔgcs1in comparison to the levels found in mice infected with theC. neoformanswild type, and their levels were also dependent on the SK1-S1P pathway. Taken together, these results suggest that the SK1-S1P pathway promotes host defense againstC. neoformansinfections by regulating cytokine levels, promoting extracellular killing by phagocytes, and generating a granulomatous response.

Asymptomatic Carriage of Group A Streptococcus Is Associated with Elimination of Capsule Production

ABSTRACTHumans commonly carry pathogenic bacteria asymptomatically, but despite decades of study, the underlying molecular contributors remain poorly understood. Here, we show that a group A streptococcus carriage strain contains a frameshift mutation in thehasAgene resulting in loss of hyaluronic acid capsule biosynthesis. This mutation was repaired by allelic replacement, resulting in restoration of capsule production in the isogenic derivative strain. The “repaired” isogenic strain was significantly more virulent than the carriage strain in a mouse model of necrotizing fasciitis and had enhanced growthex vivoin human blood. Importantly, the repaired isogenic strain colonized the mouse oropharynx with significantly greater bacterial burden and had significantly reduced ability to internalize into cultured epithelial cells than the acapsular carriage strain. We conducted full-genome sequencing of 81 strains cultured serially from 19 epidemiologically unrelated human subjects and discovered the common theme that mutations negatively affecting capsule biosynthesis arisein vivoin thehasoperon. The significantly decreased capsule production is a key factor contributing to the molecular détente between pathogen and host. Our discoveries suggest a general model for bacterial pathogens in which mutations that downregulate or ablate virulence factor production contribute to carriage.

Insights into the Ropy Phenotype of the Exopolysaccharide-Producing Strain Bifidobacterium animalis subsp.lactisA1dOxR

ABSTRACTThe proteome of the ropy strainBifidobacterium animalissubsp.lactisA1dOxR, compared to that of its nonropy isogenic strain, showed an overproduction of a protein involved in rhamnose biosynthesis. Results were confirmed by gene expression analysis, and this fact agreed with the high rhamnose content of the ropy exopolysaccharide.