I have no first hand experience with it.
en.wikipedia.org/wiki/ImipenemB.B. is not classified as gram negative OR positive, but....here's a quote about
that:
" When Borrelia burgdorferi is Gram-stained, the cells stain a weak Gram-negative by default, as safranin is the last dye used. Borrelia, like most spirochetes, does have an outer membrane that contains an LPS-like substance, an inner membrane, and a periplasmic space which contains a layer of peptidoglycan. Therefore, it has a Gram-negative bacterial type cell wall, despite its staining characteristics."