Control of microbial growth week7

Masdiana Padaga

10/04/23

Bacterial growth 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

10/04/23Masdiana Padaga

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


Bactericidal - kills bacteria Bacteristatic - inhibits bacterial growth

Fungicidal Fungistatic Algacidal Algastatic


Temperature Desiccation Osmotic pressure Radiation

1. HeatMoist Heat

Boiling Water Steam Heat (Autoclave)

Dry Heat Direct Flaming Incineration Hot Air Sterilization (Oven)

2. Filtration 3. Radiation

Ionizing RadiationNon-Ionizing Radiation

4. Pasteurization (Heat)


1. Heatworks 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


• Sterilization is the killing of all organisms, including viruses. Heat is the most widely used method of sterilization. Often, however, we cannot attain sterility, but we can still control microorganisms effectively by limiting 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 shows the relationship between temperature and the rate of killing as indicated by the decimal reduction time for two different microorganisms.

1. Boiling Waterkills vegetative

bacterial cells, Fungi and many viruses

not effective for endospores and some viruses Hepatitis (20 min)

Some spores may survive boiling water for up to 20 hrs

2. Autoclave (Steam under pressure)preferred method of

sterilizationWater boils at 100 C Increasing the

pressure raises the Temp.

15 lbs./ per sq. inch (psi) ------> 121 C

121 C for 15 min.


• An autoclave permits application of steam heat under pressure at temperatures above the boiling point of water, 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 SterilizationOven ( 170 C for 2 hours)used on substances that would be

damaged by moist heat sterilization gauzes, dressings or powders


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 Radiationgamma rays & x-rays

penetrates most substances penetrate solid or light-absorbing materials,

Used on substances that could be damaged by heat

is widely used for sterilization and decontamination in the medical and food industriesplastic petri dishes, plastic syringes, catheterssurgical gloves


2. Non-Ionizing RadiationUV Light

does not penetrate plastic, glass or proteinaceous matter

Used to reduce microbial populationshospital rooms, nurseries, operating rooms used to decontaminate surfaces and

materials that do not absorb light, such as air and water.


• Controlled doses of electromagnetic radiation effectively inhibit microbial growth. Table 20.1 shows the radiation sensitivity of microorganisms and biological functions.

• The relationship between the survival fraction and the radiation dose is 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)


Removes microorganisms from solutions that might be damaged by heat

culture mediaenzymesvaccinesantibiotics


• Membrane filters (Figure 20.7) are used for sterilization of heat-sensitive liquids, and nucleation filters are used to isolate specimens for electron microscopy.

Refrigeration is bacteriostatic Most pathogens do not grow

Exception? Freezing: slow freezing creates ice crystals

Desiccation : bacteriostatic lyophilization used to preserve cultures

Osmotic pressure – high concentrations of salt or sugar

Molds and yeasts most resistant

• Chemicals that kill organisms are called cidal agents.

• these agents are termed •Bacteriocidal : killing bacteria,

• fungicidal,: killing fungi

•viricidal : killing viruses

Bacteriocidal agents bind tightly to their cellular targets and are not removed by dilution; but lysis, the loss of cell integrity and release of contents, does not occur.



• 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 the smallest amount of agent needed to inhibit the growth of a test organism, a value called the minimum inhibitory concentration (MIC) (Figure 20.11).

• Sterilants, disinfectants, and sanitizers are compounds used to decontaminate nonliving material. • Disinfection is the elimination of microorganisms from inanimate objects or surfaces. Table 20.3. Industrial uses of chemical antimicrobial•Antiseptics and germicides are used to reduce microbial growth on living tissues. •Table 20.4 lists some antiseptics, sterilants, disinfectants, and sanitizers.

Factors effect Antimicrobial Activity

Targets of Antimicrobial Agents

1. Temp2. Time3. Concentration of

Antimicrobial agent4. Type of Microbe5. Activity of Microbe6. Presence of organic

matter

1. Cell membrane2. Enzymes &

Proteins3. DNA & RNA


Technology

Control of microbial growth week7