Bacterialgrowth is increase in cell numbers Growth depends on temperature, pH, osmotic pressure, oxygen, and nutrients Log phase cultures are most sensitive to growth inhibition
1. Physical 2. Chemical Masdiana Padaga 03/04/12
Sterilization vs. Disinfection Sterilization destroying all forms of life Disinfection destroying pathogens or unwanted organisms Disinfectant vs. Antiseptic Disinfectant antimicrobial agent used on inanimate objects Antiseptic antimicrobial agent used on living tissue Masdiana Padaga 03/04/12
1. Heat works by denaturing enzymes and proteins A. Thermal Death Point (TDP) lowest temp. at which all microorganism in a liquid culture are killed in 10 minutes B. Thermal Death Time (TDT) minimum length of time in which all microorganisms in a liquid culture are killed at a given temperature Masdiana Padaga 03/04/12
• Sterilization is the killing of all organisms, includingviruses. Heat is the most widely used method ofsterilization. Often, however, we cannot attain sterility,but we can still control microorganisms effectively bylimiting their growth, the process of inhibition.• Death from heating is an exponential function,occurring more rapidly as the temperature rises(Figure 20.1).
•Figure 20.2 showsthe relationshipbetweentemperature andthe rate of killingas indicated by thedecimal reductiontime for twodifferentmicroorganisms.
1. Boiling Water 2. Autoclave (Steam kills vegetative under pressure) bacterial cells, Fungi preferred method of and many viruses sterilization not effective for Water boils at 100 C endospores and some Increasing the pressure viruses Hepatitis (20 raises the Temp. min) 15 lbs./ per sq. inch Some spores may (psi) ------> 121 C survive boiling water 12 1 C f o r for up to 20 hrs 15 m i n . Masdiana Padaga 03/04/12
•An autoclave permits application of steam heat underpressure at temperatures above the boiling point ofwater, killing endospores (Figure 20.3).
1. Direct Flaming Inoculating Loop and Needle 100% effective 2. Incineration disposable wastes (paper cups, bags, dressings) 3. Hot Air Sterilization Oven ( 170 C for 2 hours) used on substances that would be damaged by moist heat sterilization gauzes, dressings or powders Masdiana Padaga 03/04/12
Dry heat sterilizes. a. Hot air ovens (160-170°C/2-3 hours) used when moisture is undesirable. b. Incineration (burning) used to destroy disposable items, soiled dressings, tissue specimens etc. @ 800°C to 6500°C c. The hottest part of a Bunsen burner flame reaches 1,870°C for flaming during lab. Microbiology is Fun!
1. Ionizing Radiation gamma rays & x-rays penetrates most substances penetrate solid or light-absorbing materials, Used on substances that could be damaged by heat iswidely used for sterilization and decontamination in the medical and food industries plastic petri dishes, plastic syringes, catheters surgical gloves Masdiana Padaga 03/04/12
2. Non-Ionizing Radiation UV Light does not penetrate plastic, glass or proteinaceous matter Used to reduce microbial populations hospital rooms, nurseries, operating rooms used to decontaminate surfaces and materials that do not absorb light, such as air and water. Masdiana Padaga 03/04/12
•Controlled doses of electromagnetic radiationeffectively inhibit microbial growth. Table20.1 shows the radiation sensitivity ofmicroorganisms and biological functions.
• The relationship between the survival fraction and the radiation doseis illustrated in Figure 20.5.
does not sterilize liquids but reduces microbial load killing most pathogens and inhibiting the growth of spoilage microorganisms.Mycobacterium tuberculosis 63 C for 30 minutes 72 C for 15 seconds (HTST) Masdiana Padaga 03/04/12
Removes microorganisms from solutions that might be damaged by heat culture media enzymes vaccines antibiotics Masdiana Padaga 03/04/12
• Membrane filters (Figure 20.7) are used for sterilization ofheat-sensitive liquids, and nucleation filters are used to isolatespecimens for electron microscopy.
Refrigeration is bacteriostatic Most pathogens do not grow Exception?Freezing: slow freezing creates ice crystals
Desiccation : bacteriostatic lyophilization used to preserve culturesOsmotic pressure – high concentrations of salt or sugarMolds and yeasts most resistant
• Chemicals that kill Bacteriocidal agents organisms are bind tightly to their called cidal agents. cellular targets and are not removed by• these agents are dilution; but lysis, termed the loss of cell • Bacteriocidal : integrity and release killing bacteria, of contents, does not • fungicidal,: occur. killing fungi • viricidal : killing viruses Masdiana Padaga 03/04/12
• Agents that do not kill but only inhibit growth are called static agents, and these include bacteriostatic, fungistatic, and viristatic agents.Antimicrobial activity is measured by determining thesmallest amount of agent needed to inhibit the growth ofa test organism, a value called the minimum inhibitoryconcentration (MIC) (Figure 20.11). Masdiana Padaga 03/04/12
• Sterilants, disinfectants, and sanitizers arecompounds used to decontaminate nonlivingmaterial.• Disinfection is the elimination of microorganismsfrom inanimate objects or surfaces. Table 20.3.Industrial uses of chemical antimicrobial•Antiseptics and germicides are used to reducemicrobial growth on living tissues.•Table 20.4 lists some antiseptics, sterilants,disinfectants, and sanitizers.
Factors effect Targets ofAntimicrobial AntimicrobialActivity Agents1. Temp 1. Cell membrane2. Time 2. Enzymes &3. Concentration of Proteins Antimicrobial agent 3. DNA & RNA4. Type of Microbe5. Activity of Microbe6. Presence of organic matter Masdiana Padaga 03/04/12