Figure 1. Alpha- and delta-hemolysin activities of S. aureus strain 68111.

A plate-based screening method that capitalizes on beta-hemolysin-mediated effects on alpha- and delta-hemolysin activities was used to examine extracellular production of these toxins in MSSA68111. For this, beta-hemolysin-producing S. aureus strain RN4220 was streaked vertically on sheep blood agar. MSSA68111 (top) and two laboratory control strains (α-hemolysin^low/δ-hemolysin^- [middle] and α-hemolysin⁺/δ-hemolysin⁺ [bottom]) were then streaked perpendicularly to RN4220. Hemolysis was assessed after 24 hrs incubation at 37°C (no cold shock applied). At the junction between the test strains and RN4220, alpha-hemolysin activity is inhibited (arrowhead); the presence of delta-hemolysin is observed as an enhanced area of hemolysis (arrows).