Lecture 25 Flashcards
What are stressed/injured cells in microorganisms (MO)?
Stressed microorganisms become structurally damaged and are viable but not culturable like normal cells. They can resuscitate in a favorable environment and become functionally normal. They cannot replicate in selective environments that undamaged cells can tolerate.
What causes injury to microorganisms?
Processing and handling
Heating/thermal treatment
Chilling, refrigeration, cold shock
Dehydration/drying (lowering water activity)
Exposure to chemical preservatives or antimicrobials
Nutrient starvation
What are the types of injury in stressed microorganisms?
Leakage of cellular components: Membrane damage causes cells to lose internal solutes.
Secondary stresses: Increased sensitivity to salts, toxic chemicals, antibiotics, acids, and low pH due to membrane damage.
Cold shock: Rapid cooling of mesophiles (37°C to 0°C) can kill or injure cells.
Degradation of ribosomes and RNA
Decreased enzyme activity due to protein damage.
Extended lag phase after stress, especially freezing.
How do stressed cells resuscitate in microbiological analytical procedures?
Analytical methods must detect both normal and injured cells. There is no universal resuscitation medium. Complex media are recommended to allow damaged organisms to utilize a wider choice of substrates for recovery.
What are examples of procedures for the resuscitation of stressed cells?
Liquid repair: Hold product homogenate in saline for 2 hours at 25°C before analysis.
Liquid non-selective pre-enrichment: Inoculate into non-selective broth (e.g., TSB), incubate briefly, then proceed with selective enumeration.
Solid medium repair (double agar technique): Plate sample into non-selective medium (e.g., TSA), resuscitate, then overlay with selective medium.
Replica technique for membrane filtration: Collect cells on a membrane, place it on non-selective medium for repair, then transfer to selective medium for incubation.
