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Microbiology: Microbial Growth, Media, and Decontamination

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Termini in questo insieme (46)

  • What process do most prokaryotes use to divide? Is it sexual or asexual?
    Most prokaryotes divide by binary fission, which is an asexual process.
  • How do certain fungi and some bacteria divide? Sexual or asexual?
    Certain fungi and some bacteria divide by budding, which is an asexual process.
  • How many bacteria after 3 hours starting with one bacterium dividing every 30 minutes?
    After 3 hours (6 divisions), there would be 2^6 = 64 bacteria.
  • List the four phases of bacterial growth and what occurs in each.
    Lag phase: cells metabolically active but not dividing.
    Log phase: exponential cell division.
    Stationary phase: growth rate slows; nutrients deplete.
    Death phase: cells die faster than they divide.
  • Which bacteria grow at human body temperature (37°C)?
    Mesophiles grow optimally at 37°C; many human pathogens belong here.
  • What does the term thermophile mean?
    Thermophiles are organisms that love heat and grow best at high temperatures, typically above 45°C.
  • Name prokaryote groups by pH range.
    Acidophiles: pH 0-5.5
    Neutrophiles: pH 5.5-8
    Alkaliphiles: pH 8-11.5
  • What type of bacteria live in the Great Salt Lake?
    Halophiles thrive in high salt concentrations like the Great Salt Lake.
  • Define extremophile.
    An extremophile is an organism that thrives in extreme environmental conditions.
  • What reaction does catalase perform?
    Catalase converts hydrogen peroxide (H2O2) into water and oxygen: 2H2O2 → 2H2O + O2.
  • What reaction does superoxide dismutase perform?
    Superoxide dismutase converts superoxide radicals into oxygen and hydrogen peroxide: 2O2- + 2H+ → O2 + H2O2.
  • Which organism has no ability to detoxify reactive oxygen species (ROS)?
    Obligate anaerobes lack enzymes to detoxify ROS and cannot tolerate oxygen.
  • How do heterotrophs and autotrophs obtain carbon?
    Heterotrophs obtain carbon from organic compounds.
    Autotrophs obtain carbon from inorganic CO2.
  • What do phototrophs and chemotrophs use for energy?
    Phototrophs use light energy.
    Chemotrophs use chemical compounds for energy.
  • List three physical states of growth media and their main uses.
    Liquid (broth): growing large numbers.
    Semi-solid: motility testing.
    Solid (agar): isolating colonies.
  • Define complex media and defined media.
    Complex media: contains unknown exact chemical composition (e.g., yeast extract).
    Defined media: contains precise known chemical components.
  • What is the purpose of differential media?
    Differential media distinguish microbes based on biochemical differences, such as color changes.
  • Which agar differentiates microbes by their ability to lyse red blood cells?
    Blood agar differentiates microbes by hemolysis patterns.
  • Differentiate alpha, beta, and gamma hemolysis.
    Alpha: partial RBC lysis, greenish color.
    Beta: complete RBC lysis, clear zone.
    Gamma: no hemolysis.
  • What organisms does Mannitol Salt Agar (MSA) select for and differentiate?
    MSA selects for halotolerant staphylococci and differentiates by mannitol fermentation (yellow color change).
  • What organisms does Eosin Methylene Blue (EMB) agar select for and differentiate?
    EMB selects for Gram-negative bacteria and differentiates by lactose fermentation (metallic green or pink colonies).
  • What type of organism grows in thioglycolate media?
    Thioglycolate media supports growth of anaerobic and microaerophilic bacteria by reducing oxygen.
  • Why use aseptic techniques?
    To prevent contamination of cultures and maintain sterile conditions.
  • What is the purpose of the streak plate technique?
    To isolate individual bacterial colonies from a mixed culture.
  • Define colony.
    A colony is a visible cluster of genetically identical bacteria growing on solid media.
  • List three direct and three indirect methods of counting bacteria.
    Direct: plate counts, microscopic counts, flow cytometry.
    Indirect: turbidity, dry weight, metabolic activity.
  • What is the downside of turbidity measurement for bacteria counting?
    Turbidity cannot distinguish between live and dead cells.
  • Difference between disinfection and sterilization?
    Disinfection reduces pathogens but may not kill spores.
    Sterilization kills all microbes including spores.
  • What is decimal reduction time (DRT)?
    Time required to kill 90% of microbes at a given temperature.
  • What is thermal death time?
    Shortest time to kill all microbes at a specific temperature.
  • What is thermal death point?
    Lowest temperature that kills all microbes in a sample within 10 minutes.
  • What process uses heat, steam, and pressure to sterilize media and instruments?
    Autoclaving sterilizes using steam under pressure.
  • What microbes does boiling water for 5 minutes kill? What does it not destroy?
    Boiling kills most vegetative cells but does not destroy endospores.
  • What process reduces bacteria in milk in the dairy industry?
    Pasteurization reduces bacterial load without sterilizing.
  • What sterilization method is used when flaming an inoculation loop?
    Dry heat sterilization via direct flame.
  • What microbial decontamination method does a LifeStraw use?
    Filtration removes microbes physically.
  • Difference between disinfectants and antiseptics?
    Disinfectants are used on inanimate objects; antiseptics are safe for living tissue.
  • Difference between microbiocidal and microbiostatic germicides?
    Microbiocidal kill microbes; microbiostatic inhibit growth without killing.
  • Mode of action of alcohols like ethanol or isopropanol?
    Alcohols denature proteins and disrupt cell membranes.
  • What type of chemical does Lysol contain?
    Lysol contains phenolic compounds as disinfectants.
  • One of the most widely used halogen disinfectants?
    Chlorine is a widely used halogen disinfectant.
  • What does it mean that detergents are amphipathic molecules?
    Detergents have both hydrophobic and hydrophilic parts.
  • Which two chemical agents kill Mycobacterium?
    Phenol and chlorine compounds are effective against Mycobacterium.
  • Most effective method to eliminate endospores?
    Autoclaving is the most effective endospore elimination method.
  • How are naked viruses usually inactivated?
    Naked viruses are usually inactivated by chemical disinfectants and heat.
  • How are prions eliminated?
    Prions require strong chemical treatments and extended autoclaving at higher temperatures.