Staphylococcus aureus capsule: Production, function, and regulation

Staphylococcus aureus is a major opportunistic pathogen that causes a wide spectrum of human and animal diseases. Capsule is one of the key virulence factors of S. aureus. Approximately 90% of S. aureus isolates produce capsular polysaccharides (CPs) that envelop the entire bacterial cells. CPs can suppress the phagocytosis of S. aureus by innate immune cells, promote intracellular survival, and reduce the killing efficacy of antimicrobial agents. As a result, CPs are versatile candidates for vaccine development. The synthesis of S. aureus CPs is controlled by the cap operon, which contains 16 genes encoding functional enzymes involved in the biosynthesis and transport of CPs. During S. aureus growth, cap operon expression is strictly regulated. The control region of the cap operon is characterized by two promoters: a housekeeping sigma factor A (SigA)-dependent promoter and a stress-responsive sigma factor B-dependent promoter. Many transcription factors, including both positive and negative regulatory molecules, are timely involved in the regulatory network of S. aureus capsule synthesis. Moreover, environmental conditions such as medium composition and carbon dioxide levels further modulate CP production. In this review, the structure and function of S. aureus CPs are introduced, and the biosynthesis of S. aureus CPs is discussed. Moreover, the regulation of S. aureus CP production is summarized, the factors affecting CP production are outlined, and the preparation of S. aureus CPs is reviewed. The advanced information presented here may provide useful references for further research on the production and function of S. aureus CPs.