FIG. 4.

Flow cytometric characterization of E. coli NM522(pML1) with regard to SSC and DiBAC₄(3)-derived fluorescence after chemical and heat treatment and comparison to the bacterial populations (a) detected 20 min after lysis induction: nonlysed, polarized cells (A); nonlysed, depolarized cells (B); and bacterial ghosts (C). (Note: panel a corresponds to Fig. 3, +20 min.) Log-phase growing cells were treated with heat (b), ethanol (c), 2,4-dinitrophenol (d), pore-forming colicin E1 (e), formaldehyde (f), or ampicillin (g). An aliquot of growing cells was subjected to a procedure developed by Lam and colleagues (13) for the preparation of outer membrane fractions of H. influenzae (h). The cytometric analysis data, which are derived from 10⁴ bacterial particles (b to h) or the particles within 0.1 μl of the lysing culture (a), are presented as contour plots (SSC versus green fluorescence in arbitrary units [a.u.], both on a logarithmic scale) excluding debris and the background signal.