Production of the
transformants. A, detection of β-lactamase activity by Cephinase™ paper disk assay in spiroplasmas transformed by pSTP2 (empty vector), pSTBl1, and pSTBl2. B, secretion and diffusion of free β-lactamase in the culture medium at 24, 48 and 72 h post-inoculation. Numbers above the arrows indicate the diameter (in mm) of the S. citri (white arrow) and E. coli (black arrows) growing areas.