9/18/2016 Oxygen toxicity damages nucleic acid Repair of Injured Bacterial Cells Recovery: -add detoxifying agents such as catalase to Requires RNA and protein synthesis the medium Lag phase is prolonged -Grow anaerobically Environmental factors influence the extent and rate of repair ·Example -Listeria monocytogenes injured at 55C,20 mins Starts repair immediately at 370C and is complete in 9h 冒 园 At 40C,repair is delayed for 8-10 days and is complete in 16-19 days Viable but Non-Culturable (VBNC) Viable but Non-Culturable (VBNC) Defined-VBNC bacteria Most often induced by nutrient cannot be cultured on any limitation medium but still cause Also induced by salt concentration disease exposure to hypochlorite,and shifts in Vegetative cells differentiate temperature into a dormant cell as a How the VBNC state occurs is mostly survival strategy for non- unknown sporulating bacteria Estimated that 99%of the bacteria in VBNC cells are found in the biosphere may be VBNC marine,soil,and gastrointestinal environments 9/18/2016 8 • Oxygen toxicity – damages nucleic acid • Recovery: - add detoxifying agents such as catalase to the medium - Grow anaerobically 29 Repair of Injured Bacterial Cells • Requires RNA and protein synthesis • Lag phase is prolonged • Environmental factors influence the extent and rate of repair • Example - Listeria monocytogenes injured at 550C, 20 mins - Starts repair immediately at 370C and is complete in 9h - At 40C, repair is delayed for 8-10 days and is complete in 16-19 days 30 Viable but Non-Culturable (VBNC) • Defined - VBNC bacteria cannot be cultured on an y medium but still cause disease • Vegetative cells differentiate into a dormant cell as a survival strategy for non￾sporulating bacteria • VBNC cells are found in marine, soil, and gastrointestinal environments 31 Viable but Non-Culturable (VBNC) • Most often induced by nutrient limitation • Also induced by salt concentration, exposure to hypochlorite, and shifts in temperature • How the VBNC state occurs is mostly unknown • Estimated that 99% of the bacteria in the biosphere may be VBNC 32