Figure 11

Schematic evolution of infection towards gangrenous mastitis. The purple line represents the evolution with time of the bacterial concentration, and also symbolizes the evolution towards gangrenous mastitis, which is tightly linked to the bacterial concentration. High concentration allows S. aureus to produce high amounts of pore-forming toxins (red line), among which leukotoxins inhibit the phagocytic killing (green line) by the phagocytes recruited in milk, whereas α-toxin contributes to the ischemic necrosis that results in gangrenous mastitis. The dividing line corresponds to the critical bacterial concentration that allows bacteria to overwhelm the recruited phagocytes, and to impede phagocytic killing. The microphotographs show (from left to right) images of S. aureus phagocytosed by neutrophils, rafts of staphylococci and intoxicated neutrophils, and the typical appearance of neutrophils intoxicated by LukMF′ (with swollen and rounded nucleus).