Publication
Within-host evolution of bovine Staphylococcus aureus selects for a SigB-deficient pathotype characterized by reduced virulence but enhanced proteolytic activity and biofilm formation
Publisher:
Springer Science and Business Media LLC
Date:
17-09-2019
DOI:
10.1038/S41598-019-49981-6
Abstract: Staphylococcus aureus is a major cause of bovine mastitis, commonly leading to long-lasting, persistent and recurrent infections. Thereby, S . aureus constantly refines and permanently adapts to the bovine udder environment. In this work, we followed S . aureus within-host adaptation over the course of three months in a naturally infected dairy cattle with chronic, subclinical mastitis. Whole genome sequence analysis revealed a complete replacement of the initial predominant variant by another isogenic variant. We report for the first time within-host evolution towards a sigma factor SigB-deficient pathotype in S . aureus bovine mastitis, associated with a single nucleotide polymorphism in rsbU (G368A → G122D), a contributor to SigB-functionality. The emerged SigB-deficient pathotype exhibits a substantial shift to new phenotypic traits comprising strong proteolytic activity and poly- N -acetylglucosamine (PNAG)-based biofilm production. This possibly unlocks new nutritional resources and promotes immune evasion, presumably facilitating extracellular persistence within the host. Moreover, we observed an adaptation towards attenuated virulence using a mouse infection model. This study extends the role of sigma factor SigB in S . aureus pathogenesis, so far described to be required for intracellular persistence during chronic infections. Our findings suggest that S . aureus SigB-deficiency is an alternative mechanism for persistence and underpin the clinical relevance of staphylococcal SigB-deficient variants which are consistently isolated during human chronic infections.