Bacterial Growth Phases
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Questions and Answers

What is the term used to describe the time taken by bacteria to double in number during a specified time period?

  • Stationary phase
  • Doubling time (correct)
  • Generation phase
  • Growth rate

    • During which phase of bacterial growth do antibiotics act most effectively?

  • Exponential phase
  • Lag phase
  • Decline or Death phase
  • Stationary phase (correct)

    • What happens to the number of cell divisions and cell deaths during the stationary phase?

  • Number of cell deaths = 0
  • Number of cell divisions = number of cell deaths (correct)
  • Number of cell divisions > number of cell deaths
  • Number of cell divisions < number of cell deaths

    • What occurs during the decline or death phase of bacterial growth?

    <p>Individual bacteria begin to die due to unfavorable conditions</p> Signup and view all the answers

    What is the primary purpose of an artificial culture medium?

    <p>To support the growth of microorganisms or cells</p> Signup and view all the answers

    What is true about bacteria that can survive in the environment by producing endospores?

    <p>They can survive for long periods of time in the absence of nutrients</p> Signup and view all the answers

    What is the most commonly used solidifying agent in solid media?

    <p>Agar</p> Signup and view all the answers

    What is the term used to describe bacteria that are unable to synthesize all of their growth requirements from common mineral nutrients and simple carbohydrates?

    <p>Auxotrophs</p> Signup and view all the answers

    What is the temperature at which agar melts?

    <p>95°C</p> Signup and view all the answers

    What is a factor that can affect bacterial growth?

    <p>All of the above</p> Signup and view all the answers

    What is the main drawback of using liquid media?

    <p>Both A and B</p> Signup and view all the answers

    What is produced by bacteria during the stationary phase?

    <p>Exotoxins and antibiotics</p> Signup and view all the answers

    What is the concentration of agar typically used in culture media?

    <p>1-3%</p> Signup and view all the answers

    What is the purpose of using semi-solid agar?

    <p>To demonstrate bacterial motility and separate motile from non-motile strains</p> Signup and view all the answers

    What happens to the growth rate during the stationary phase?

    <p>It stabilizes</p> Signup and view all the answers

    What is the term for a culture system that comprises both liquid and solid medium in the same bottle?

    <p>Biphasic media</p> Signup and view all the answers

    What is the term for the process of inoculation in liquid medium that helps to dilute any inhibitors of bacterial growth?

    <p>Dilution method</p> Signup and view all the answers

    What is the main advantage of using agar in culture media?

    <p>It solidifies at 42°C and doesn't contribute any nutritive property</p> Signup and view all the answers

    What is the primary source of infection for Toxoplasma gondii?

    <p>Eating undercooked meat of sheep and cows containing viable trophozoites</p> Signup and view all the answers

    What is the most common symptom of Toxoplasma gondii infection in immunocompromised individuals?

    <p>Severe recrudescence of the infection</p> Signup and view all the answers

    What is the primary route of transmission for congenital Toxoplasma gondii infection?

    <p>Through the placenta during pregnancy</p> Signup and view all the answers

    What is the typical size range of nematodes?

    <p>Typically less than 2.5 millimeters long</p> Signup and view all the answers

    What is the largest nematode parasitizing the human intestine?

    <p>Ascaris lumbricoides</p> Signup and view all the answers

    What is the primary cause of blindness in newborns due to Toxoplasma gondii infection?

    <p>Congenital infections</p> Signup and view all the answers

    What is the lung phase of Ascaris lumbricoides infection also known as?

    <p>Ascaris pneumonitis</p> Signup and view all the answers

    What is the primary effect of a large number of Ascaris lumbricoides adults in the intestine?

    <p>Intestinal blockage and malnutrition</p> Signup and view all the answers

    What is the life cycle of Ascaris lumbricoides composed of?

    <p>Two phases: lung and intestinal</p> Signup and view all the answers

    What is the habitat of Taenia saginata, also known as Beef Tapeworms?

    <p>Small intestine— (ileum)</p> Signup and view all the answers

    What is the length that an adult tapeworm can grow up to in the lumen of the intestine?

    <p>Up to 25 meters</p> Signup and view all the answers

    What is the intermediate host of Taenia saginata?

    <p>Cattle</p> Signup and view all the answers

    What is the distinctive external feature of Trematodes?

    <p>Presence of two suckers</p> Signup and view all the answers

    What is the clinical symptom of a high infection of Taenia saginata?

    <p>Diarrhea and constipation</p> Signup and view all the answers

    How do humans acquire Taenia saginata?

    <p>Through the ingestion of raw or poorly cooked meat of infected cows</p> Signup and view all the answers

    What is the life span of an adult Taenia saginata?

    <p>1 to 2 years</p> Signup and view all the answers

    How many eggs can a female Taenia saginata produce per day?

    <p>200,000 eggs</p> Signup and view all the answers

    What is the time period for the development of Taenia saginata from egg to mature adult?

    <p>2 months</p> Signup and view all the answers

    What is the primary mode of transmission of Schistosomiasis?

    <p>Direct skin penetration</p> Signup and view all the answers

    What is the intermediate host of Schistosomiasis?

    <p>Snails</p> Signup and view all the answers

    What is the main cause of damage to the intestinal wall in Intestinal Schistosomiasis?

    <p>The host's inflammatory response to eggs deposited at the site</p> Signup and view all the answers

    What is the site of infection in Urinary tract Schistosomiasis?

    <p>Veins of the urinary bladder</p> Signup and view all the answers

    What is the result of the eggs' secretion of proteolytic enzymes in Intestinal Schistosomiasis?

    <p>Further damage to the tissue</p> Signup and view all the answers

    What is the clinical symptom of Intestinal Schistosomiasis?

    <p>GI bleeding</p> Signup and view all the answers

    How many types of Schistosomiasis exist?

    <p>Two</p> Signup and view all the answers

    In which part of the venous system do adult Schistosomes take up residence?

    <p>Abdominal veins</p> Signup and view all the answers

    How many people are affected by Schistosomiasis globally?

    <p>200 million</p> Signup and view all the answers

    Which method of single cell isolation requires the microorganisms to withstand temporary exposure to the 42-45°C temperature of the liquid agar medium?

    <p>Pour Plate Method</p> Signup and view all the answers

    In which method of single cell isolation do subsurface colonies develop within the agar medium?

    <p>Pour Plate Method</p> Signup and view all the answers

    What is the primary purpose of the Serial Dilution Method?

    <p>To obtain pure cultures of microorganisms that grow only in liquid media</p> Signup and view all the answers

    In the Spread Plate Method, how are the microorganisms diluted?

    <p>In a series of tubes containing sterile liquid</p> Signup and view all the answers

    What is the primary advantage of using pure culture techniques?

    <p>It provides results that are easier to interpret</p> Signup and view all the answers

    What is a disadvantage of the Pour Plate Method?

    <p>The picking up of subsurface colonies interferes with other colonies</p> Signup and view all the answers

    What is the minimum number of cells required for a colony to be visible to the naked eye?

    <p>1 million cells</p> Signup and view all the answers

    What is a common application of the Pour Plate Method?

    <p>To determine the number of viable bacterial cells present in a culture</p> Signup and view all the answers

    Which method of single cell isolation involves spreading a diluted bacterial suspension evenly over the surface of an agar plate?

    <p>Spread Plate Method</p> Signup and view all the answers

    Which method involves plating of diluted samples mixed with melted agar medium?

    <p>Pour Plate Method</p> Signup and view all the answers

    What is the purpose of re-streaking isolated colonies onto fresh media?

    <p>To ensure the purity of the culture</p> Signup and view all the answers

    What is the main difference between the Streak Plate Method and the Pour Plate Method?

    <p>The method of inoculation</p> Signup and view all the answers

    What is the advantage of using the Streak Plate Method over other methods of single cell isolation?

    <p>It is a simpler method to perform</p> Signup and view all the answers

    What is the purpose of using a solid culture medium in pure culture techniques?

    <p>To provide a surface for single cells to grow into colonies</p> Signup and view all the answers

    What is the primary objective of the serial dilution method in microbiology?

    <p>To isolate a single microorganism from a mixed culture</p> Signup and view all the answers

    Which of the following methods is used to pick out a single cell from a mixed culture?

    <p>Micromanipulator method</p> Signup and view all the answers

    What is the advantage of the micromanipulator method over the capillary pipette method?

    <p>It allows for the selection of specific strains within a species</p> Signup and view all the answers

    What is the purpose of using a sterile glass-coverslip in the capillary pipette method?

    <p>To observe the microorganism under the microscope</p> Signup and view all the answers

    Which of the following is a characteristic of the serial dilution method?

    <p>It involves the inoculation of a series of tubes with a microbial suspension</p> Signup and view all the answers

    What is the advantage of using the serial dilution method to isolate a single microorganism?

    <p>There is a high probability that the growth in a tube results from a single microorganism</p> Signup and view all the answers

    What is the outcome of using the serial dilution method?

    <p>A pure culture of a single microorganism</p> Signup and view all the answers

    What is the purpose of adding extra nutrients in the form of blood, serum, or egg yolk to basal media?

    <p>To support the growth of fastidious bacteria</p> Signup and view all the answers

    What is the term used to describe media that are designed to inhibit unwanted commensal or contaminating bacteria?

    <p>Selective media</p> Signup and view all the answers

    What is the purpose of using egg yolk and serum as solidifying agents in culture media?

    <p>To solidify the liquid medium</p> Signup and view all the answers

    What is the term used to describe media that have a well-known composition of every component?

    <p>Synthetic media</p> Signup and view all the answers

    What is the purpose of using differential media or indicator media?

    <p>To recognize different bacteria based on their colony color</p> Signup and view all the answers

    What is the term used to describe media that are used to inhibit commensals in a clinical specimen?

    <p>Enrichment media</p> Signup and view all the answers

    What is the purpose of using agar in culture media?

    <p>To solidify the liquid medium</p> Signup and view all the answers

    During which phase of bacterial growth do the enzymes and intermediates accumulate until they are present in a concentration that permits growth to start?

    <p>Lag phase</p> Signup and view all the answers

    What is the primary reason for the increase in the lag phase when bacteria are transferred from a nutritionally rich medium to a poor medium?

    <p>Bacteria take time to adapt to the new medium</p> Signup and view all the answers

    During which phase of bacterial growth do the bacteria replicate by binary fission at a constant rate?

    <p>Exponential or Logarithmic phase</p> Signup and view all the answers

    What is the result of the exhaustion of nutrients or accumulation of toxic metabolic products during the exponential or logarithmic phase?

    <p>Inhibition of growth</p> Signup and view all the answers

    What is the pattern of growth observed during the exponential or logarithmic phase?

    <p>Exponential</p> Signup and view all the answers

    What is the number of bacteria during the exponential or logarithmic phase proportional to?

    <p>The number of generations</p> Signup and view all the answers

    What is the term used to describe the orderly increase of all the chemical constituents of the bacteria?

    <p>Bacterial growth</p> Signup and view all the answers

    What is the primary purpose of using serial dilution method in microbiology?

    <p>To isolate a single microbial cell</p> Signup and view all the answers

    Which of the following methods is used to measure the viable count of microorganisms?

    <p>All of the above</p> Signup and view all the answers

    What is the primary advantage of using semi-solid agar in microbiology?

    <p>To separate motile from non-motile strains</p> Signup and view all the answers

    What is the term used to describe a culture system that comprises both liquid and solid medium in the same bottle?

    <p>Biphasic media</p> Signup and view all the answers

    What is the primary limitation of using liquid media in microbiology?

    <p>All of the above</p> Signup and view all the answers

    What is the most commonly used solidifying agent in solid media?

    <p>Agar</p> Signup and view all the answers

    What is the term used to describe the process of inoculation in liquid medium that helps to dilute any inhibitors of bacterial growth?

    <p>Dilution method</p> Signup and view all the answers

    What is the primary purpose of using agar in culture media?

    <p>To solidify the medium</p> Signup and view all the answers

    What is the classification of bacterial culture media based on?

    <p>All of the above</p> Signup and view all the answers

    What is the term used to describe the growth of microorganisms or cells in a culture medium?

    <p>Culture medium</p> Signup and view all the answers

    Study Notes

    Bacterial Growth

    • Generation time or doubling time: the time taken by bacteria to double in number during a specified time period
    • This time period tends to vary with different bacteria
    • Antibiotics are most effective during this stage

    Phases of Bacterial Growth

    • Stationary phase: nutrients are used up, resulting in the accumulation of toxic waste materials and inhibitory compounds; cell number remains stable; production of exotoxins, antibiotics, metachromatic granules, and spore formation take place
    • Decline or Death phase: bacteria lose their ability to reproduce, and death occurs rapidly and exponentially; some bacteria can survive by producing endospores or using breakdown products of dead bacteria as nutrients

    Factors Affecting Bacterial Growth

    • Nutritional requirement: bacteria require certain nutrients for growth; some can synthesize their requirements, while others are auxotrophs
    • Physical/environmental factors: temperature, pH, and other environmental factors can affect bacterial growth

    Bacterial Culture Media

    • Classification: based on consistency (liquid, semi-solid, solid, or biphasic), nutritional composition, and functional use/purpose
    • Liquid media: used for obtaining viable counts, but may not show bacterial properties and cannot detect multiple types of bacteria
    • Solid media: agar is the most commonly used solidifying agent; it doesn't contribute to bacterial growth and is available as fibers or powders
    • Semi-solid media: useful for demonstrating bacterial motility and separating motile from non-motile strains
    • Biphasic media: combines liquid and solid media in the same bottle

    Parasitology

    • Nematodes: slender, worm-like animals; some are microscopic, while others can be up to 5 cm long
    • Ascaris lumbricoides: the largest nematode parasitizing the human intestine; found worldwide, especially among people with low living standards and children
    • Clinical symptoms: asymptomatic in small numbers, but can cause malnutrition, intestinal blockage, and pulmonary symptoms in large numbers
    • Life cycle: has two phases (lung and intestinal); takes 2 months from egg to mature adult, with each female producing 200,000 eggs per day
    • Cestodes (Tapeworms): ribbon-shaped, multi-segmented flatworms; dwell in the human small intestine
    • Taenia saginata (Beef Tapeworms): causes taeniasis; habitat is the small intestine; transmission is through ingestion of raw or poorly cooked meat of infected cows
    • Morphology: adult is divided into three parts (head, neck, and segments); can grow up to 25 meters in length
    • Clinical symptoms: diarrhea, constipation, vomiting, loss of appetite, and anemia
    • Trematodes: flattened oval or worm-like animals; usually no more than a few centimeters in length; distinctive feature is the presence of two suckers
    • Schistosomiasis (Bilharzia): a disease of the venous system; acquired through contaminated water; affects up to 200 million people worldwide
    • Transmission: direct skin penetration; eggs hatch and develop inside snails, which then penetrate human skin
    • Pathology: damage to the intestinal wall and urinary tract due to inflammatory response to eggs and proteolytic enzymes
    • Clinical picture: GI bleeding, diarrhea, liver damage, and hematuria

    Pure Culture Techniques

    • A pure culture is a population of cells or multicellular organisms growing in the absence of other species or types.
    • Result obtained using pure cultures are much easier to interpret, but the organism sometimes behaves differently as they do in their natural environment.
    • Basic requirements for obtaining a pure culture: a solid culture medium, a media container that can be maintained in an aseptic condition, and a method to separate individual bacterial cells.
    • A colony is a mass of cells descended from the original one, and about 1 million cells are required for a colony to be easily visible to the naked eye.

    Methods for Obtaining Pure Culture

    • Streak Plate Method: a small amount of mixed culture is placed on the tip of an inoculation loop/needle and is streaked across the surface of an agar medium.
    • Pour Plate Method: the mixed culture of bacteria is diluted directly in tubes containing melted agar medium, and the contents of each tube are poured into separate Petri plates.
    • Spread Plate Method: a drop of diluted liquid from each tube is placed on the center of an agar plate and spread evenly over the surface by means of a sterilized bent-glass-rod.
    • Serial Dilution Method: the inoculum is subjected to serial dilution in a sterile liquid medium, and a large number of tubes of sterile liquid medium are inoculated with aliquots of each successive dilution.
    • Single Cell Isolation Methods:
      • Capillary pipette method: an individual cell of the required kind is picked out from the mixed culture and is permitted to grow.
      • Micromanipulator method: a single cell is picked out from a mixed culture using a micromanipulator.

    Bacterial Growth

    • Growth of bacteria is the orderly increase of all the chemical constituents of the bacteria, resulting in an increase in cell size and cell mass.
    • Death of bacteria is the irreversible loss of ability to reproduce.

    Bacterial Growth Curve

    • The growth curve indicates multiplication and death of bacteria, and it consists of four phases: lag phase, exponential or logarithmic phase, stationary phase, and decline or death phase.
    • Lag phase: adaptation phase, where bacteria are not able to replicate, and enzymes and intermediates are formed and accumulated.
    • Exponential or logarithmic phase: bacteria are in a rapidly growing and dividing state, and their metabolic activity increases.

    Culture Media

    • Classification of culture media:
      • Based on consistency: liquid, semi-solid, solid, and biphasic.
      • Based on nutritional composition: simple, complex, and synthetic (or defined).
      • Based on functional use or application: basal media, enriched media, selective media, enrichment media, and differential media.
    • Examples of culture media: nutrient agar, blood agar, peptone water, Davis & Mingioli medium, etc.
    • Ingredients of culture media: water, agar, peptone, casein hydrolysate, meat extract, yeast extract, and malt extract.

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