Microbiology Quiz: Biofilms and Cultures
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Questions and Answers

What is one of the final steps in biofilm formation?

  • Dispersal of cells from a mature biofilm (correct)
  • Channel formation
  • Metabolic differentiation of microbes
  • Adhering to plastic media

    • Biofilms are often associated with acute infections and decreased resistance to antimicrobial treatments.

    False (B)

    Name one type of medical device on which biofilms can form.

    catheters, prosthetic joints, and pacemakers

    Cardinal temperatures include the minimum, maximum, and ______ growth temperatures for a given organism.

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

    Match the following items related to biofilms and their function:

    <p>Biofilms = Can be used to break down pollutants Cardinal Temperatures = Affect bacterial growth Medical Devices = Surfaces where biofilms can form Mushroom-like Columns = Structures formed within biofilms</p> Signup and view all the answers

    Which type of culture medium is designed to inhibit the growth of unwanted organisms while allowing the target organism to grow?

    <p>Selective (D)</p> Signup and view all the answers

    Liquid broths are used for isolating and observing colonies.

    <p>False (B)</p> Signup and view all the answers

    What is the purpose of using semi-solid media in laboratory cultures?

    <p>motility studies</p> Signup and view all the answers

    A visible cluster of microorganisms that originates from a single microbial cell growing on a solid medium is called a ______.

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

    Match the following methods with their primary purpose in assessing microbial numbers:

    <p>Microscopic counts = Enumerating total cells present Spread-plate = Viable counting of cells by colony formation Pour-plate = Viable counting of cells mixed within agar Optical density = Turbidimetric measure of cell numbers</p> Signup and view all the answers

    Which method involves spreading a diluted culture over the surface of an agar plate to count viable cells?

    <p>Spread-plate (D)</p> Signup and view all the answers

    Optical Density is a direct method of counting viable cells.

    <p>False (B)</p> Signup and view all the answers

    In the context of microbiology, what does 'fastidious' mean when describing organisms?

    <p>requiring complex nutritional requirements</p> Signup and view all the answers

    Which of the following is NOT a phase of the microbial growth curve?

    <p>Dormant phase (C)</p> Signup and view all the answers

    During the stationary phase of microbial growth, the rate of cell growth is significantly higher than the rate of cell death.

    <p>False (B)</p> Signup and view all the answers

    What is the main component of the matrix in which cells are enmeshed within a biofilm?

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

    A chemostat enables control over both the specific ______ rate and growth yield of a microbial culture.

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

    Match the biofilm formation step with the corresponding event:

    <p>Attachment = Planktonic cells adhere to a surface Colonization = Microbes grow and produce extracellular polysaccharides Development = Cells in the biofilm change their metabolism</p> Signup and view all the answers

    What is $N_0$ in the equation $N_t = N_0 * 2^n$?

    <p>Initial cell number (D)</p> Signup and view all the answers

    The lag phase is characterized by rapid cell division and exponential growth.

    <p>False (B)</p> Signup and view all the answers

    What cellular structures often mediate the initial attachment of planktonic cells to a surface during biofilm formation?

    <p>flagella, fimbriae, or pili</p> Signup and view all the answers

    What does CFU stand for in microbiology?

    <p>Colony Forming Units (A)</p> Signup and view all the answers

    Turbidity decreases with an increase in the number of microbial cells in a suspension.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the process where a cell enlarges to twice its size and then divides?

    <p>Binary fission</p> Signup and view all the answers

    The time required for a population of microbial cells to double is known as the ______ time.

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

    In the context of plate counts, what is the ideal range for the number of colonies on a plate to be considered valid?

    <p>30-300 (D)</p> Signup and view all the answers

    A batch culture is an open system where nutrients are continuously replenished.

    <p>False (B)</p> Signup and view all the answers

    Match the term with its definition:

    <p>Turbidity = Cloudiness of a liquid caused by microbial cells scattering light Septum = Structure separating dividing cells Growth = Increase in the number of cells Batch culture = A closed system microbial culture of fixed volume</p> Signup and view all the answers

    Which of the following is a limitation when using plate counts to quantify bacteria?

    <p>Some bacteria form clumps or biofilms (C)</p> Signup and view all the answers

    Which of the following is a molecular adaptation found in organisms thriving in cold environments?

    <p>Greater polar amino acid content in proteins (B)</p> Signup and view all the answers

    Thermophiles thrive in environments with optimal temperatures below 45°C.

    <p>False (B)</p> Signup and view all the answers

    What is the optimal growth pH range for neutrophiles?

    <p>5.5-8</p> Signup and view all the answers

    The enzyme _____ isolated from Thermus aquaticus is widely used in PCR.

    <p>Taq polymerase</p> Signup and view all the answers

    Match the adaptation with the temperature class of organisms:

    <p>Higher content of unsaturated fatty acids = Psychrophiles More ionic bonding = Thermophiles Optimal temperature &lt; 15ºC = Psychrophiles Optimal temperature &gt; 45ºC = Thermophiles</p> Signup and view all the answers

    Which structural feature contributes to the stability of membranes in thermophiles?

    <p>Higher proportion of long-chain fatty acids (B)</p> Signup and view all the answers

    Acidophiles thrive in alkaline or basic environments.

    <p>False (B)</p> Signup and view all the answers

    Which of the following describes adaptations of cold-active enzymes?

    <p>Less hydrophobic amino acid content (C)</p> Signup and view all the answers

    Which of the following describes Bacillus natronophilus?

    <p>Alkaliphilic bacterium isolated from soda lakes (B)</p> Signup and view all the answers

    Helicobacter pylori is an acidophile.

    <p>False (B)</p> Signup and view all the answers

    What do halophiles require for growth?

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

    Aerotolerant anaerobes are unable to respire $O_2$, but their growth is ______ by it.

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

    What is used by alkaliphiles like Bacillus natronophilus to drive transport reactions, instead of $H^+$?

    <p>$Na^+$ (A)</p> Signup and view all the answers

    Molecular oxygen ($O_2$) is directly toxic to all cells.

    <p>False (B)</p> Signup and view all the answers

    What enzyme do aerobic and aerotolerant cells have that destroy ROS?

    <p>ROS scavenging enzymes</p> Signup and view all the answers

    Match the following organisms with their oxygen requirements:

    <p>Aerobe = Requires $O_2$ for respiration Microaerophile = Requires $O_2$ at levels reduced from that in air Obligate anaerobe = Cannot grow in the presence of $O_2$ Facultative = Can grow in either the presence or absence of $O_2$</p> Signup and view all the answers

    Flashcards

    Culture Medium

    A nutrient solution for growing microorganisms in a lab.

    Selective Medium

    Inhibits unwanted organism growth while allowing specific targets.

    Differential Medium

    Distinguishes organisms based on biochemical reactions.

    Enrichment Medium

    Contains extra nutrients for fastidious organisms to grow.

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    Colonies

    Visible clusters of microorganisms that grow from single cells.

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    Total Cell Count

    Enumeration of all cells present using microscopy.

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    Spread-Plate Method

    A technique where diluted culture is spread on agar for colony growth.

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    Pour-Plate Method

    A known volume of culture mixed with molten agar to count colonies.

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    Biofilm Formation

    The process where microorganisms adhere to surfaces and form structured communities.

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    Dispersal in Biofilms

    Mature biofilms release cells to colonize new environments.

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    Biofilms in Infections

    Biofilms are linked to chronic infections and drug resistance.

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    Biofilms in Medical Devices

    Biofilms can develop on devices like catheters and prosthetics, causing complications.

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    Cardinal Temperatures

    The minimum, maximum, and optimum temperatures for bacterial growth.

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    Colony Forming Units (CFUs)

    Individual cells or groups of cells that can form a visible colony.

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    Turbidity

    Cloudiness of a liquid caused by suspended microbial cells scattering light.

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    Binary fission

    A process of cell division where a cell divides into two identical daughter cells.

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    Generation time

    The time it takes for a microbial population to double in number.

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    Batch culture

    A closed system for growing microorganisms with a fixed volume and limited nutrients.

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    Great plate count anomaly

    Observation that direct counts of microbes often exceed those recoverable on culture plates.

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    Biofilms

    Assemblages of microbes that adhere to surfaces and form protective layers.

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    Septum

    The partition that forms between dividing cells during binary fission.

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    Psychrophiles

    Organisms that thrive in cold environments (optimal temp < 15ºC).

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    Cold-active enzymes

    Enzymes optimized for function at low temperatures, with flexible structures.

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    Thermophiles

    Organisms that thrive in hot environments (optimal temp < 45ºC).

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    Heat-stable enzymes

    Enzymes that remain functional at high temperatures due to structural adaptations.

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    Acidophiles

    Organisms that grow optimally at low pH levels (e.g., pH 0.7).

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    Alkaliphiles

    Organisms that prefer high pH environments and can produce useful enzymes.

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    Cryopreservants

    Substances used to protect cells from damage during freezing.

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    Lipid monolayers

    Single layers of lipids in membranes, enhancing stability at high temperatures.

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    Bacillus natronophilus

    An alkaliphilic bacterium found in soda lakes with high carbonate levels.

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    Sodium motive force

    Mechanism where sodium ions (Na+) drive transport reactions in bacteria.

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    Urease

    An enzyme produced by H. pylori that breaks down urea into ammonia and CO2.

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    Halophiles

    Organisms that require high salt concentrations (like NaCl) for growth.

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    Aerobes

    Organisms that use oxygen (O2) in their respiration process.

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    Microaerophiles

    Organisms that require low levels of oxygen to survive.

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    Obligate anaerobes

    Organisms that cannot grow in the presence of oxygen.

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    Reactive Oxygen Species (ROS)

    Toxic oxygen by-products that can harm cells if not managed.

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    Microbial Growth Curve

    A graphical representation of microbial population growth over time, consisting of four distinct phases.

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    Lag Phase

    The initial phase where bacteria adapt to their environment before division begins.

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    Exponential Phase

    The phase of rapid cell division where the population doubles regularly.

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    Stationary Phase

    The phase where growth rate equals death rate, resulting in a stable population size.

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    Decline Phase

    The phase where cell death outnumbers growth, leading to a decrease in population.

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    Nt (Cell Number at Time t)

    Represents the total cell count at a specific time in the growth cycle.

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    Chemostat

    A continuous culture device that regulates microbial growth rate and yield.

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    Study Notes

    Microbial Growth

    • Microbial growth is the increase in population size from cell division.
    • Binary fission is the process of cell division where a cell grows to twice its size and then divides into two identical cells.

    Cell Nutrition

    • Macronutrients are required in large quantities for bacteria.
    • Average bacterial cell weight is 10⁻¹² g and 75% is water.
    • Carbon, oxygen, nitrogen, hydrogen, phosphorus, and sulfur make up about 96% of dry weight.
    • Potassium, sodium, calcium, magnesium, chlorine, and iron make up the remaining 3.7% of dry weight.
    • Micronutrients are required in minute amounts.
    • The elements needed for microbes are essential to all microorganisms.
    • Some trace metals are used for special functions.
    • Others are unnecessary but metabolized, and still other are unnecessary and not metabolized.

    Growth Media and Laboratory Culture

    • Culture medium is a nutrient solution for growing specific microorganisms in a laboratory.
    • Defined media has a known chemical composition.
    • Complex media has unknown nutrient quantities, often derived from natural sources like yeast extract or peptone.
    • Examples of complex media include nutrient agar and tryptic soy broth.
    • Defined media is used for genetic studies, and complex media is a source of C, N, vitamins, growth factors, trace elements, and minerals.
    • Selective media inhibits the growth of unwanted organisms, while allowing a specific target organism to grow.
    • Differential media distinguishes between organisms based on special biochemical reactions.
    • Examples are agar for Salmonella and blood agar for hemolysis.
    • Enrichment media contains additional nutrients to support the growth of fastidious organisms.

    Laboratory Culture

    • Liquid media (broths) are used for growing large numbers of microorganisms.
    • Solid media contains agar to solidify the medium, used for isolating and observing colonies.
    • Semi-solid media contains lower agar concentrations, and is useful for motility studies.
    • Colonies are visible clusters of microorganisms that originate from a single microbial cell on solid media.
    • Samples inoculated from mixed cultures or contaminated pure cultures typically contain more than one colony type.

    Assessing Microbial Numbers

    • Microscopic counts enumerate microbial cells.
    • Spread plate, pour plate, and optical density are methods for viable counting, where viable cells form colonies.
    • Dilution of samples can affect viability.

    Turbidimetric Measures of Microbial Cell Numbers

    • Turbidity is a measure of cloudiness due to light scattering by microbial cells, where more cells lead to higher turbidity.
    • Optical density, or OD, is a measure of turbidity that can be quantitatively assessed about different cell numbers.

    Limitations of Microbial Growth Measurements

    • Some bacteria form clumps or biofilms, affecting measurements, which may indicate inaccurately how many cells are present.

    Dynamics of Microbial Growth

    • Growth is the increase in the number of cells through cell division.
    • Binary fission is a major process of cell division, where one cell splits into two identical cells.
    • Generation time is the time required for a microbial population to double.

    Growth Cycle

    • Batch culture is a closed-system microbial culture with a fixed volume and limited nutrients.
    • Microbial growth profile is called the microbial growth curve.

    Phases of the Microbial Growth Curve

    • Lag phase is the delay at the beginning of growth, prior to the onset of growth.
    • Exponential phase refers to the growth period when the growing cell population doubles at regular intervals.
    • Stationary phase is the period when the rate of growth and death are approximately equal.
    • Decline phase is the period when the rate of cell death exceeds the rate of cell growth.

    Quantitative Aspects of Microbial Growth

    • The equation Nt = N₀2^n describes the relationship between cell number at time t (Nt), initial cell number (N₀), and the number of generations (n).

    Continuous Culture

    • A chemostat is a continuous culture device that allows for precise control over specific growth rate and growth yield of microbial cultures.

    Biofilms

    • Biofilms are populations of cells embedded in a polysaccharide matrix, attached to a surface.
    • Biofilm formation is a process beginning with attachment, colonization, development, and dispersal.
    • Biofilms are often associated with chronic infections.

    Environmental Effects on Growth: Temperature

    • Cardinal temperatures are minimum, maximum, and optimal growth temperatures for a given organism.
    • Psychrophiles have an optimal temperature below 15°C, mesophiles between 20°C-45°C, thermophiles greater than 45°C, and hyperthermophiles even higher temperatures.

    Molecular Adaptations to Life in the Cold

    • Cold-active enzymes possess significant structural alterations, such as more a-helix presence, greater polar and lesser hydrophobic amino acid content, membrane fatty acids with higher unsaturated and shorter chain characteristics to maintain semifluid state and cryopreservants to prevent crystal formation.
    • Slime can also be indicative.

    Molecular Adaptations to Life at High Temperatures

    • Heat-stable enzymes from thermophiles possess special amino acid sequences and solute concentration differences such as di-inositol phosphate, diglycerol phosphate, higher content of long-chain saturated fatty acids, and lipid-layered differences from their mesophilic counterparts.

    Effect of pH on Microbial Growth

    • Acidophiles thrive in acidic environments and alkaliphiles in alkaline environments.
    • Helicobacter pylori uses urease to neutralize stomach acid.
    • Alkaliphiles are often from soda lakes or those with high concentrations of carbonate salts.
    • Molecular adaptations for alkaliphilic growth include sodium, instead of hydrogen ions, driving transport reactions. These adaptations allow them to maintain a neutral cytoplasm in alkaline pH.

    Effects of Osmolarity on Microbial Growth

    • Halophiles require NaCl for growth, while halo-tolerant microbes can withstand high salt concentrations.

    Effect of Oxygen on Microbial Growth

    • Aerobes use oxygen in respiration, whereas anaerobes cannot.
    • Microaerophiles require lower oxygen levels, while aerotolerant anaerobes are unaffected by oxygen.
    • Obligate anaerobes cannot grow in the presence of oxygen.

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