Control of Bacterial Control of Bacterial GrowthGrowth Definitions– Sterilization - Processes that kills living

organisms including spores– Disinfection - Destruction of vegetative

pathogens (not spores) on inanimate surfaces

– Antisepsis –A chemical method of disinfection from skin and mucus membranes

– Degerming - Removal of microbes from a limited area (alcohol swab prior to injection)

– Sanitization – The removal of microbes from eating utensils and food preparation areas

Control of Bacterial Control of Bacterial GrowthGrowth Factors that influence

effectiveness of antimicrobial treatment– Number– Environmental Influences– Time of exposure– Inherent characteristics

Control of Bacterial Control of Bacterial GrowthGrowth Physical Methods of Control

– Temperature Effects (Hot & Cold)– Filtration– Desiccation– Osmotic Pressure & High Pressure– Radiation

See chart page 197

Control of Bacterial Control of Bacterial GrowthGrowth Effects of Temperature

– Moist Heat– Dry Heat– Pasteurization– Refrigeration

Control of Bacterial Control of Bacterial GrowthGrowth Thermal Death Point (TDP) lowest

temperature at which all microbes in liquid suspension will be killed with 10 min of exposure

Thermal Death Time (TDT) minimal length of time for all bacteria in liquid culture to be killed at a given temperature

Decimal Reduction Time (DRT) Time in which 90% of a population at a given temperature will be killed

Control of Bacterial Control of Bacterial GrowthGrowth Temperature - Moist Heat

– Autoclave: 120-130°C (15-20 lbs/in2)– Effect on instruments– Foil or cloth wrap solid materials– Must use on liquids

Control of Bacterial Control of Bacterial GrowthGrowth Temperature - Dry Heat

– Glassware and instruments– 160-170°C for at least 90 min– Usually foil wrap– Incineration (loops & needles)

Control of Bacterial Control of Bacterial GrowthGrowth Temperature - Pasteurization

– Milk: 63°C for 30 min (old)– Milk: 72°C for 15 sec (new)– Juices

Control of Bacterial Control of Bacterial GrowthGrowth Temperature - Refrigeration

– Does not usually kill– Slows metabolism although

psychrophillic organisms can still grow– Best between 0° and 7° C– Freeze thaw cycles can kill some

organisms– Used for culture preservation– Lyophilization or freeze-drying long term

storage – effective in preserving foods

Control of Bacterial Control of Bacterial GrowthGrowth Filtration

– Used for heat sensitive liquids like serum or urea containing media

– 0.45µ or 0.22µ pores in membrane– Often used commercially with beer,

wine and fruit juices

Control of Bacterial Control of Bacterial GrowthGrowth Desiccation

– Inhibits growth more than kills– Dried meats and vegetables– Freeze dry processes in foods

Control of Bacterial Control of Bacterial GrowthGrowth Osmotic Pressure

– High concentrations of salts or sugars inhibit growth of bacteria; examples includes jams and jellies, sugar and salt cured meats

High Pressure – High pressure is transferred evenly

throughout culture suspension can denature proteins & glycoproteins

Radiation & Control of Microorganisms

Control of Bacterial Control of Bacterial GrowthGrowth Radiation

– Short wave (X-rays, gamma rays) high penetration power; breaks DNA

– Non-ionizing (UV) longer wave; no penetrating power; forms thymine dimers

– Organisms contain multiple repair systems