Phenotypes of mecillinam-resistant mutants grown in PYE medium alone (−Mec) and PYE medium plus mecillinam (+Mec). Cells shown are representative of the whole population. (A) YB1964 (mec-1101), PYE medium; (B) YB1964 (mec-1101), PYE medium plus 5 μg of mecillinam per ml; (C) YB1980 (mec-1165), PYE medium; (D) YB1980 (mec-1165), PYE medium plus 3 μg of mecillinam per ml. Magnification, ×6,400 (all panels). Negatives were scanned with a Umax Super Vista S-12 scanner by using Adobe Photoshop 3.0.5 software.