CP and infection: Capsule polysaccharide expression in vivo was further explored by evaluating whether RNA transcripts from the cap operon could be detected in mouse blood following infection with a representative panel of USA300 (two in vivo CP-positive isolates, PFESA0119 and PFESA0029 [CDC3] and an in vivo CP-negative isolate, PFESA0021) and USA500 (in vivo CP-positive isolate PFESA0065) isolates.