Microbiology Unit 3 Review Lectures 21, 22, & 23 – Control of Microbial Growth Terms Used Sometimes these words are used interchangeably; however there are imp distinctions to note Sterilization = kills all viable organisms, including bacterial endospores and inactive viruses o Sterilization is a different concept than other terms—means a COMPLETE absence of a living organisms that could infect the cell ABSOLUTE term Yes or no—something can’t be semi-sterile All the other terms are more general and mean removing micro-organisms on some level o Disinfection = removal of microbes from an inanimate surface o Antisepsis = removal of microbes from a living surface o Sanitation = reducing populations to safe levels o Decontamination = treatment to make objects safe to handle Just because something is sanitized, etc., doesn’t mean that all of the microorganisms have been removed—which is ok most of the time—sterilization isn’t always necessary Control Measures Control measures may have different effects Microbistatic —causes cells to stop growing o Microbes wont be able to grow/divide; however, it does NOT mean that they will die—so if you remove the control agent, the microbes could start growing again Microbicidial —kills cells o These cells can never grow again Micobilytic —kills cells w/ lysis o Imp that it lyses the cells—causes cell to burst bc the organelles, etc. are released when this happens ° Microbial Susceptibility to Control Measures Varies 1
Not all microorganisms are equally susceptible to all controls Most resistant : prions & bacterial endospores o Prions—not organisms but infectious proteins o They are HARD to deactivate; aren’t living Moderate resistance : protest cysts, some fungal spores, naked viruses, Mycobacterium, Staphylococcus, Pseudomonas o Cysts—survival forms of protists that are more resistant than vegetative cells Least resistant : most vegetative bacterial cells, most fungal spores, fungal and protist vegetative cells, enveloped viruses Features such as a waxy cell capsule, etc. may increase a microbe’s resistance ° Clicker Question Which bacterium might be the most difficult to control? o Bacillus—is an endospore ********* o Cells that are most resistant are hardest to control ° Physical & Chemical Means for Controlling Microbial Growth: ° High Temp is Very Effective One very common way to control microbial growth is via heating—this eliminates contaminating microorganisms If you need something to be sterile, you need to be concerned about destroying all endospores—need to do more than just boiling—killing endospores to ensure sterilization requires temps above 100°C, so increased pressure is often used Autoclave = a machine that reaches temps high enough to kill microbes – 20 to 30 min is usually enough time Moist heat is better than dry heat High temps kill most microbes; very high temps even kill endospores ° Pasteurization or Mild Heating
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- Spring '08