Controlling Microbial World In Vitro, Summaries of Biology

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• Draw a bacterial growth curve and label its four phases
• Cite two reasons why bacteria die during the death phase
• Name three ways in which obligate intracellular pathogens can be cultured in the laboratory
• List three in vitro sites where microbial growth must be inhibited
• Differentiate among sterilization, disinfection, and sanitization
• Explain the processes of pasteurization and lyophilization
• List several physical methods used to inhibit the growth of microorganisms

• Cite three ways in which disinfectants kill microorganisms
• Identify several factors that can influence the effectiveness of disinfectants
• Explain briefly why the use of antibiotics in animal feed and household products is controversial

✓ Microbial growth is affected by many different environmental factors, including the: ✓ availability of nutrients and ✓ moisture, ✓ temperature, ✓ pH, ✓ osmotic pressure, ✓ barometric pressure, and ✓ composition of the atmosphere.

• All living organisms require nutrient the various chemical compounds that organisms use to sustain life. Therefore, to survive in a particular environment, appropriate nutrients must be available.
• Many nutrients are energy sources; organisms will obtain energy from these chemicals by breaking chemical bonds.
• Nutrients also serve as sources of carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur as well as other elements (e.g., sodium; potassium; chlorine; magnesium calcium; and trace elements such as iron, iodine, and zinc)that are usually required in lesser amounts.

• Every microorganism has an optimum growth temperature the temperature at which the organism grows best.
• Every microorganism also has a minimum growth temperature, below which it ceases to grow, and a maximum growth temperature, above which it dies.
• The temperature range (i.e., the range of temperatures from the minimum growth temperature to the maximum growth temperature) at which an organism grows can differ greatly from one microbe to another.

• Microorganisms that grow best at high temperatures are called thermophiles (meaning organisms that love heat).
• Microbes that grow best at moderate temperatures are called mesophiles.
• Psychrophiles prefer cold temperatures. They thrive in cold ocean water. At high altitudes, algae (often pink) can be seen living on snow.
• Ironically, the optimum growth temperature of one group of psychrophiles (called psychrotrophs) is refrigerator temperature (4°C); perhaps you encountered some of these microbes (bread molds, for example) the last time you cleaned out your refrigerator.
• Microorganisms that prefer warmer temperatures but can tolerate or endure very cold temperatures and can be preserved in the frozen state, are known as psychroduric organisms.

Osmotic pressure is the pressure that is exerted on a cell membrane by solutions both inside and outside the cell.

• When the concentration of solutes in the environment outside of a cell is greater than the concentration of solutes inside the cell, the solution in which the cell is suspended is said to be hypertonic.
• Osmosis is defined as the movement of a solvent (e.g., water), through a permeable membrane, from a solution having a lower concentration of solute to a solution having a higher concentration of solute.

• If the cell is a human cell, such as a red blood cell (erythrocyte), the loss of water causes the cell to shrink; this shrinkage is called crenation, and the cell is said to be crenated
• Plasmolysis, inhibits bacterial cell growth and multiplication.
• When the concentration of solutes outside a cell is less than the concentration of solutes inside the cell, the solution in which the cell is suspended is said to be hypotonic.
• If sufficient water enters, the cell will burst (lyse). In the case of erythrocytes, this bursting is called hemolysis.
• If the pressure become so great that the cell ruptures, the escape of cytoplasm from the cell is referred to as plasmoptysis.
• When the concentration of solutes outside a cell equals the concentration of solutes inside the cell, the solution is said to be isotonic.

• Most bacteria are not affected by minor changes in barometric pressure. Barometric

pressure is the measurement of air pressure in the atmosphere.

• Others, known as piezophiles, thrive deep in the ocean and in oil wells, where the atmospheric pressure is very high. Some archaea, for example, are piezophiles, capable of living in the deepest parts of the ocean.

• Microorganisms vary with respect to the type of gaseous atmosphere that they require. For example, some microbes (obligate aerobes) prefer the same atmosphere that humans do (i.e., about 20%–21% oxygen and 78%–79% nitrogen, with all other atmospheric gases combined representing less than 1%).

• There are many reasons why the growth of microbes is encouraged in microbiology laboratories.
• For example, technologists and technicians who work in clinical microbiology laboratories must be able to isolate microorganisms from clinical specimens and grow them on culture media so they can then gather information that will enable identification of any pathogens that are present.

• In many ways, modern microbiology laboratories resemble those of 50, 100, or even 150 years ago.
• Today’s laboratories still use many of the same basic tools that were used in the past.
• For example, microbiologists still use compound light microscopes, Petri dishes containing solid culture media, tubes containing liquid culture media, Bunsen burners, wire inoculating loops, bottles of staining reagents, and incubators.