104 ◾ Fundamental Food Microbiology
irreversibly injured (dead) cells. Their relative percentages vary greatly and are dependent on the
species and strains, nature of suspending media, nature and duration of stress, and methods of
detection. Injured cells differ in the level of injury and in several characteristics from their normal counterparts. One of these is increased sensitivity to many compounds to which normal
cells are resistant, such as surface-active compounds (bile salts, deoxycholate, or SDS), NaCl,
table 10.1 Cells and Spores of Some Microorganisms important in Food in Which
Sublethal injury is Detected
Gram-positive pathogenic bacteria: Sta. aureus, Clo. botulinum, Lis. monocytogenes, Clo.
perfringens, Bac. cereus
Gram-negative pathogenic bacteria: Salmonella, Shigella spp., enteropathogenic Esc. coli, Esc.
coli O157:H7, Vib. parahaemolyticus, Cam. jejuni, Yer. enterocolitica, Aer. hydrophila
Gram-positive spoilage bacteria: Clo. sporogenes, Clo. bifermentum, Bac. subtilis, Bac.
stearothermophilus, Bac. megaterium, Bac. coagulans
Gram-negative spoilage bacteria: Pseudomonas spp., Serratia spp.
Gram-positive bacteria used in food bioprocessing: Lac. lactis, Lab. delbrueckii subsp.
bulgaricus, Lab. acidophilus
Gram-positive indicator bacteria: Ent. faecalis
Gram-negative indicator bacteria: Esc. coli, Enterobacter aerogenes, Klebsiella spp.
Bacterial spores: Clo. botulinum, Clo. perfringens, Clo. bifermentum, Clo. sporogenes, Bac.
cereus, Bac. subtilis, Bac. stearothermophilus, Des. nigrificans
Yeasts and molds: Sac. cerevisiae, Candida spp., Asp. flavus
(a)
(c)
(b)
0.5 µm
Figure 10.3 transmission electron microscopic photographs showing the alteration of morphology of Lis. monocytogenes cells following exposure to stress conditions of (b) high temperature (45°C for 16 hours) or (c) 5.5% naCl. Control cells (a) appeared normal. (Adapted from
Geng, t. et al., J. Appl. Microbiol., 95, 4, 2003. With permission.)
irreversibly injured (dead) cells. Their relative percentages vary greatly and are dependent on the
species and strains, nature of suspending media, nature and duration of stress, and methods of
detection. Injured cells differ in the level of injury and in several characteristics from their normal counterparts. One of these is increased sensitivity to many compounds to which normal
cells are resistant, such as surface-active compounds (bile salts, deoxycholate, or SDS), NaCl,
table 10.1 Cells and Spores of Some Microorganisms important in Food in Which
Sublethal injury is Detected
Gram-positive pathogenic bacteria: Sta. aureus, Clo. botulinum, Lis. monocytogenes, Clo.
perfringens, Bac. cereus
Gram-negative pathogenic bacteria: Salmonella, Shigella spp., enteropathogenic Esc. coli, Esc.
coli O157:H7, Vib. parahaemolyticus, Cam. jejuni, Yer. enterocolitica, Aer. hydrophila
Gram-positive spoilage bacteria: Clo. sporogenes, Clo. bifermentum, Bac. subtilis, Bac.
stearothermophilus, Bac. megaterium, Bac. coagulans
Gram-negative spoilage bacteria: Pseudomonas spp., Serratia spp.
Gram-positive bacteria used in food bioprocessing: Lac. lactis, Lab. delbrueckii subsp.
bulgaricus, Lab. acidophilus
Gram-positive indicator bacteria: Ent. faecalis
Gram-negative indicator bacteria: Esc. coli, Enterobacter aerogenes, Klebsiella spp.
Bacterial spores: Clo. botulinum, Clo. perfringens, Clo. bifermentum, Clo. sporogenes, Bac.
cereus, Bac. subtilis, Bac. stearothermophilus, Des. nigrificans
Yeasts and molds: Sac. cerevisiae, Candida spp., Asp. flavus
(a)
(c)
(b)
0.5 µm
Figure 10.3 transmission electron microscopic photographs showing the alteration of morphology of Lis. monocytogenes cells following exposure to stress conditions of (b) high temperature (45°C for 16 hours) or (c) 5.5% naCl. Control cells (a) appeared normal. (Adapted from
Geng, t. et al., J. Appl. Microbiol., 95, 4, 2003. With permission.)