Influence of Sae-regulated and Agr-regulated factors on the escape ofStaphylococcus aureusfrom human macrophages

Abstract

Although Staphylococcus aureus is not a classical intracellular pathogen, it can survive within phagocytes and many other cell types. However, the pathogen is also able to escape from cells by mechanisms that are only partially understood. We analysed a series of isogenic S. aureus mutants of the USA300 derivative JE2 for their capacity to destroy human macrophages from within. Intracellular S. aureus JE2 caused severe cell damage in human macrophages and could efficiently escape from within the cells. To obtain this full escape phenotype including an intermittent residency in the cytoplasm, the combined action of the regulatory systems Sae and Agr is required. Mutants in Sae or mutants deficient in the Sae target genes lukAB and pvl remained in high numbers within the macrophages causing reduced cell damage. Mutants in the regulatory system Agr or in the Agr target gene psmα were largely similar to wild-type bacteria concerning cell damage and escape efficiency. However, these strains were rarely detectable in the cytoplasm, emphasizing the role of phenol-soluble modulins (PSMs) for phagosomal escape. Thus, Sae-regulated toxins largely determine damage and escape from within macrophages, whereas PSMs are mainly responsible for the escape from the phagosome into the cytoplasm. Damage of macrophages induced by intracellular bacteria was linked neither to activation of apoptosis-related caspase 3, 7 or 8 nor to NLRP3-dependent inflammasome activation.

Accessory gene regulator (Agr) functionality in Staphylococcus aureus derived from lower respiratory tract infections

“…This is in agreement with Chaffin et al , who observed hld and psm gene upregulation in a mouse model of pneumonia [38]. Furthermore, virulence genes regulated by Agr have an important function in escape from alveolar macrophages [39, 40] and neutrophils [41], both cells comprising the first line of defence in lung infections. Other groups have highlighted that Agr dysfunction is associated with persistent bacteraemia and that during growth in blood, apolipoproteins can interfere and inhibit quorum sensing and Agr activity [42].…”

Identification and Characterization of Staphylococcus aureus Strains with an Incomplete Hemolytic Phenotype

“…PCR testing found that all 60 SIHP strains possessed the tst gene suggesting increased virulence. Recently, many reports showed that S. aureus could survive in the human monocyte-derived macrophages and these S. aureus strains are more virulent (Kubica et al, 2008; Tranchemontagne et al, 2015; Münzenmayer et al, 2016; Nandi and Bishayi, 2016). Therefore, we compared the intracellular survival abilities of SIHP strains and SCHP strains which is tst negative S. aureus in macrophages, and found that intracellular survival ability of SIHP strain was much higher than that of tst negative S. aureus strain.…”

Leukocidins: staphylococcal bi-component pore-forming toxins find their receptors

“…For example, the killing of neutrophils by PVL is enhanced by the action of PSMs 8,90 . Similarly, LukAB has been found to synergize with PVL and PSMs to promote S. aureus escape from macrophages after phagocytosis 91 . Very few studies have investigated the synergy between leukocidins and other virulence factors in vivo .…”