3.5. DAPI fluorescence in treated endospores
To determine whether the divergent effects of nisin and reutericyclin on heat- and pressure-mediated spore inactivation relate
to membrane permeabilization, endospore permeability was
assayed by determination of the accessibility of DAPI to endospore
DNA. Untreated endospores of C. sporogenes and C. beijerinckii did
not stain with DAPI, indicating that endospores were impermeable
to DAPI.C. sporogenes andC. beijerinckii endosporesfluoresced after
all treatments at 90
C and 600 MPa (Fig. 5A). An average value of
76 19% and 70 23% fluorescence intensity was recorded for
endospores relative to vegetative cells of C. sporogenes and
C. beijerinckii, respectively. The observation of 100% fluorescence
intensity in vegetative cells was not expected, as endospores are
markedly smaller than vegetative cells. Following treatment at
90
C for 0e60 min, endospores of both C. sporogenes and
C. beijerinckii did not exhibit increased fluorescence after being
exposed to DAPI (Fig. 5B and data not shown). No fluorescence
was observed among samples heated at 90
C in the presence of
reutericyclin, or in the control samples. However, increased