Effect of staphylococcal delta-toxin and bee venom peptide melittin on leukotriene induction and metabolism of human polymorphonuclear granulocytes

Evolutionary genomics of Staphylococcus aureus reveals insights into the origin and molecular basis of ruminant host adaptation

Phenotypic biotyping has traditionally been used to differentiate bacteria occupying distinct ecological niches such as host species. For example, the capacity of Staphylococcus aureus from sheep to coagulate ruminant plasma, reported over 60 years ago, led to the description of small ruminant and bovine S. aureus ecovars. The great majority of small ruminant isolates are represented by a single, widespread clonal complex (CC133) of S. aureus, but its evolutionary origin and the molecular basis for its host tropism remain unknown. Here, we provide evidence that the CC133 clone evolved as the result of a human to ruminant host jump followed by adaptive genome diversification. Comparative whole-genome sequencing revealed molecular evidence for host adaptation including gene decay and diversification of proteins involved in host–pathogen interactions. Importantly, several novel mobile genetic elements encoding virulence proteins with attenuated or enhanced activity in ruminants were widely distributed in CC133 isolates, suggesting a key role in its host-specific interactions. To investigate this further, we examined the activity of a novel staphylococcal pathogenicity island (SaPIov2) found in the great majority of CC133 isolates which encodes a variant of the chromosomally encoded von Willebrand-binding protein (vWbp^Sov2), previously demonstrated to have coagulase activity for human plasma. Remarkably, we discovered that SaPIov2 confers the ability to coagulate ruminant plasma suggesting an important role in ruminant disease pathogenesis and revealing the origin of a defining phenotype of the classical S. aureus biotyping scheme. Taken together, these data provide broad new insights into the origin and molecular basis of S. aureus ruminant host specificity.

The rise and rise of Staphylococcus aureus: laughing in the face of granulocytes

Recent developments in the study of host-pathogen interactions have fundamentally altered our understanding of the nature of Staphylococcus aureus infection, and previously held tenets regarding the role of the granulocyte are being cast aside. Novel mechanisms of pathogenesis are becoming evident, revealing the extent to which S. aureus can evade neutrophil responses successfully by resisting microbicides, surviving intracellularly and subverting cell death pathways. Developing a detailed understanding of these complex strategies is especially relevant in light of increasing staphylococcal virulence and antibiotic resistance, and the knowledge that dysfunctional neutrophil responses contribute materially to poor host outcomes. Unravelling the biology of these interactions is a challenging task, but one which may yield new strategies to address this, as yet, defiant organism.

Pasteurella haemolytica leukotoxin enhances production of leukotriene B4 and 5-hydroxyeicosatetraenoic acid by bovine polymorphonuclear leukocytes

The influence of the leukotoxin of Pasteurella haemolytica on the generation of arachidonic acid metabolites by bovine polymorphonuclear leukocytes (PMNs) was investigated. PMNs released 5-, 12-, and 15-hydroxyeicosatetraenoic acids (5-, 12-, and 15-HETE) and leukotriene B4 (LTB4) upon stimulation with arachidonic acid. The leukotoxin preparations dose dependently enhanced the release of the 5-lipoxygenase products 5-HETE and LTB4 in arachidonic acid-stimulated PMNs, whereas the release of 12- and 15-HETE was not affected. The enhanced release of LTB4 and 5-HETE was not due to a decreased cellular retention of the 5-lipoxygenase products. In addition, leukotoxin preparations by themselves were also able to induce LTB4 and 5-HETE production in the absence of exogenous arachidonic acid. Generation of 5-lipoxygenase products by PMNs stimulated by leukotoxin may represent an important cellular event that occurs during infections with P. haemolytica.