Microbiology

Microbiology Study Guide

Chapter 3: Control of Microorganisms

Objectives 1. Understand principles of microbial control. 2. Describe physical methods of microbial control. 3. Explain the chemical methods of microbial control. 4. Summarize the use of chemotherapeutic agents and antibiotics for facilitating microbial control. 3.1 Principles of Microbial Control Factors Influencing the Success of Control Methods There are various factors that affect the usefulness (efficacy) of microbial control methods. These factors should be considered to devise control measures. They include: • Size of microbial population: o Death is exponential (i.e., more microbes = more time to kill the population) o Plot the log of the number of surviving microbes versus the time equal to a straight line; the slope is equal to the killing rate o Kill time can be predicted based on the initial microbe concentrations • Exposure time of the agent: o The kill rates are increased with the rise in exposure time o Complete destruction is possible when more time is invested (in the case of larger volumes) and vice versa • Effect of concentration, temperature, and pH: o When the concentration is increased, it is equivalent to an increase in exposure time o One should devise the combination of temperature, pH, and concentration at which the agent works optimally o At varied levels of pH and temperature, the agent stability needs to be considered o Legionella pnuemophila (Legionnaires disease): This is the effect of the microbe suspended in tap water and exposed to different temperatures, pH, and chlorine concentrations • Protective features of the microbes: o Endospore formers, such as C. tetani o Cysts: Protozoa o Porins: Pseudomonas o Cell wall: Mycobacterium tuberculosis (opportunistic pathogen) o Active growth versus resting cells: Antibiotics (penicillin, a transpeptidase) • Interactions and protective features afforded by the environment:

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