Chapter 8 - The Staphylococcal Hemolysins

Staphylococcus aureus and other coagulase-positive staphylococci (CoPS) are opportunistic pathogens associated with a large spectrum of diseases that range from skin and mucosal infections to life-threatening septicemias in humans and animals. They produce several extracellular proteins contributing in different way to the severity of infections. In particular, this chapter focuses on four cytotoxins: α-, β-, γ-, and Δ-hemolysins. These exotoxins can be divided into four classes based on their genetic determinants. Their ability in damaging eukaryotic cellular membranes by pore formation (driving cellular lysis) plays an important role in establishing and maintaining opportunistic infections both in human and animal hosts. The hemolytic activity also depends on the specific substrate erythrocyte utilized, ranging from total to absent hemolysis. Just as CoPS differ in possessing these toxins, toxins differ in pathogenic mechanisms, and cellular specificity and behavior, with respect to oxygen sensitivity and temperature range of action. The double α- and β-hemolytic activity on blood sheep agar plates has been proposed to discriminate among CoPS, in particular, members of the Staphylococcus intermedius Group (SIG), while the β-hemolytic activity alone is behind the use of the CAMP test to detect of Group B streptococci, Listeria and Rhodococcus equi.