The nutritional requirements of methicillin-dependent and -resistant strains of Pediococcus cerevisiae.

A new methicillin-dependent and -resistant substrain (called MRD) of Pediococcus cerevisiae was developed by serial passages followed by replica-plating. Other methicillin-resistant, but not -dependent, substrains were isolated after treatment of the same parent strain with a mutagen. A methicillin-independent partial revertant, still resistant to the drug, was isolated from the original methicillin-dependent and -resistant substrain (CRD) developed several years ago. The requirements of some of these strains for acetate, vitamins and amino acids were compared. All except the parent methicillin-sensitive strain required pantothenate for growth, but no other consistent differences were found. The parent, but not strain CRD, grew without lysine added to the medium, though 19 other amino acids were needed by each strain. Both of these strains fermented glucose to lactate (mainly the L-isomer) in the absence or presence of methicillin.