In an initial mono-infection experiment (n = 2) with our ace deletion mutant (OG1RFΔace), TX5467, we first determined the expression of cat (encoding chloramphenicol acetyl transferase) in OG1RFΔace, which carries this chloramphenicol resistance marker gene in place of ace, by analyzing individual colonies for chloramphenicol resistance and by high stringency hybridization using intragenic cat and ace DNA probes. The gene discussed is ACE; the disease is infection.