“…Many Gram-positive bacteria are dif®cult to permeabilize after ®xation with PFA (Stahl and Amann, 1991;Macnaughton et al, 1994;Amann et al, 1995). Gram-positive bacteria were detected after ®xation by heat (Jurtshuk et al, 1992), ethanol±formalin (9:1 v/v); Braun-Howland et al, 1992) or 50% ethanol (Roller et al, 1994). Treatment of PFA-®xed cells with cell wall lytic enzymes, such as lysozyme or mutanolysin, also increased the permeability of Gram-positive lactococci, enterococci and streptococci (Beimfohr et al, 1993), Streptomyces scabies hyphae (Hahn et al, 1992), and Microthrix parvicella (Erhart et al, 1997).…”