| Metabolically Injured Organsims | - injury caused by heating, freezing, drying, irradiation, chemical food preservatives, sanitizing compounds |
| Sub-lethal injury | damage can be repaired |
| Lethal injury | Results in death of the cell |
| Characteristics of injured organsims | - unable to grow in selective media
- need time to repair their injury
- sensitive to selective agents (salt, antibiotics, dyes, high T)
- some severely injured cells are oxygen sensitive
- need non-selective medium for resuscitation: incubate anaerobically to grow |
| Cellular sites of damage | - cytoplasmic membrane
- ribosomes
- enzymes
- DNA |
| Why determine number of injured cells? | - don't know # injured --> overestimate effectiveness of treatments
- injured cells can repair and retain virulence to cause disease |
| Determine injured cells in food sample | - plate sample on both non-selective and selective agar media
- incubate and count colonies on both agar media
- # injured cells = # colonies on non-selective (injured and non-injured cells) - # colonies on selective (non-injured cells) |
| Viable but "non-culturable" organisms (VNBC) | - SPC count less than actual viable population
- first noted in marine vibrios
- difficult to grow during winter months
- factors causing VBNC: drop in temp, nutrient limitation |
| Cellular changes in VBNC cells | - changes on cell lipids
- new proteins made
- rod shaped cells change to coccoid |
