Control of Bacterial Growth l 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 Growth l Factors that influence effectiveness of antimicrobial treatment –Number –Environmental Influences –Time of exposure –Inherent characteristics

Control of Bacterial Growth l Physical Methods of Control –Temperature Effects (Hot & Cold) –Filtration –Desiccation –Osmotic Pressure & High Pressure –Radiation l See chart page 197

Control of Bacterial Growth l Effects of Temperature –Moist Heat –Dry Heat –Pasteurization –Refrigeration

Control of Bacterial Growth l Thermal Death Point (TDP) lowest temperature at which all microbes in liquid suspension will be killed with 10 min of exposure l Thermal Death Time (TDT) minimal length of time for all bacteria in liquid culture to be killed at a given temperature l Decimal Reduction Time (DRT) Time in which 90% of a population at a given temperature will be killed

Control of Bacterial Growth l Temperature - Moist Heat –Autoclave: °C (15-20 lbs/in 2 ) –Effect on instruments –Foil or cloth wrap solid materials –Must use on liquids

Control of Bacterial Growth l Temperature - Dry Heat –Glassware and instruments – °C for at least 90 min –Usually foil wrap –Incineration (loops & needles)

Control of Bacterial Growth l Temperature - Pasteurization –Milk: 63°C for 30 min (old) –Milk: 72°C for 15 sec (new) –Juices

Control of Bacterial Growth l 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 Growth l 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 Growth l Desiccation –Inhibits growth more than kills –Dried meats and vegetables –Freeze dry processes in foods

Control of Bacterial Growth l Osmotic Pressure –High concentrations of salts or sugars inhibit growth of bacteria; examples includes jams and jellies, sugar and salt cured meats l High Pressure –High pressure is transferred evenly throughout culture suspension can denature proteins & glycoproteins

Radiation & Control of Microorganisms

Control of Bacterial Growth l 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