Mycoplasma

The members of Mycoplasma are remarkable in the Bacteria in which they do not have cell walls at any stage in their life cycle. They are considered to be between the smallest organisms capable of growth outside a host cell and can have a genome of less than 600 000 bp. While they are phylogenetically true Gram-positive organisms they do not retain the crystal violet–iodine complex in the Gram stain by lack of a cell wall and so appear to be Gram-negative. The  absence of a rigid  wall also renders the  cells pleiomorphic, where they  can  display various shapes under several environmental or  physiological conditions or  even  in  the  similar culture, appearing as small  cocci,  swollen rods  or branched filaments. Finally the lack of cell wall renders them resistant to antibiotics interfering with cell wall synthesis like as vancomycin and penicillin, so other antibiotics like as kanamycin must be used in combating the pathogenic species.