Ans: b (Borrelia)Ref: Ananthanarayan and Paniker's Textbook of Microbiology, 8th ed.* Treponema - do not stain by ordinary method. Prolonged Giemsa, Fontana or Levaditis method is used* Mycoplasma - has no cell wall. So they are gram negative but are better stained by Giemsa* Mycobacterium-resist decolonisation by alcohol even without mordant effect of iodine. Can be called gram positive even though it is not used for diagnosis* Borrelia - readily stain by ordinary methods and are gram negative